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Literature Review and Annotated Bibliography:

Water Requirements of Desert Ungulates 

U.S. Department of the Interior

U.S. Geological Survey

Southwest Biological Science Center

Open-File Report 2005-1141 

April 2005

In Cooperation with the University of Arizona School of Natural Resources 

and Arizona Game and Fish Department

 setalugnU treseD fo stnemeriuqeR retaW :yhpargoilbiB detatonnA dna weiveR erutaretiL

In cooperation with the University of Arizona School of Natural Resources 

and Arizona Game and Fish Department

Literature Review and Annotated Bibliography: 

Water Requirements of Desert Ungulates 

By James W. Cain III, Paul R. Krausman, Steven S. Rosenstock, and Jack C. Turner 

Open-File Report 2005-1141 

April 2005

U.S. Department of the Interior 

U.S. Geological Survey

USGS Southwest Biological Science Center 

Sonoran Desert Research Station 

University of Arizona 

School of Natural Resources 

125 Biological Sciences East 

Tucson, Arizona 85721
U.S. Department of the Interior

Gale A. Norton, Secretary 

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2005 

Note: This document contains information of a preliminary nature and was prepared primarily for internal 

use in the U.S. Geological Survey. This information is NOT intended for use in open literature prior to 

publication by the investigators named unless permission is obtained in writing from the investigators named 

and from the Station Leader.

Suggested Citation 

Cain III, J.W., P.R. Krausman, S.S. Rosenstock, J.C. Turner. 2005. Literature Review and 

Annotated Bibliography: Water Requirements of Desert Ungulates. USGS Open-File Report 2005-

1141. U.S. Geological Survey, Southwest Biological Science Center, Sonoran Desert Research 

Station, University of Arizona, Tucson, AZ. 

Cover photo: James W. Cain III, Sierra Pinta Mountains, Cabeza Prieta National Wildlife Refuge
Authors 

James W. Cain III 

University of Arizona 

School of Natural Resources 

104 Biological Sciences East 

Tucson, Arizona 85721 

Paul R. Krausman 

University of Arizona 

School of Natural Resources 

325 Biological Sciences East 

Tucson, Arizona 85721 

Steven S. Rosenstock 

Arizona Game and Fish Department 

Research Branch 

2221 W Greenway Road 

Phoenix, Arizona 85023 

Jack C. Turner 

Sam Houston State University 

P.O. Box 2116 

Huntsville, Texas 77341 

U.S. Geological Survey Station Personnel 

Charles Van Riper, III, Station Leader 

Steve P. Gloss, Ecologist 

William L. Halvorson, Research Ecologist 

Cecil R. Schwalbe, Ecologist 

Michael R. Kunzmann, Ecologist

Program and Expertise Areas of USGS and UA Personnel 

Administration & Outreach 

Cori Dolan 

Wendy Parrish 

Charles Van Riper, III

Avian Ecology 

Claire Crow 

Glenn Johnson 

Mike Kunzmann 

Chris O’Brien 

Brian Powell 

Charles van Riper, III 

Data Management 

Mike Kunzmann 

Brent Sigafus 

Ecology of Amphibians & Reptiles 

Kevin Baker 

Cristina Jones 

Dave Prival 

Phil Rosen 

Cecil Schwalbe 

Brent Sigafus 

Eric Stitt 

Fire Management 

Cori Dolan 

James Feldmann 

Bill Halvorson 

Invasive Species Research 

Patricia Guertin 

Jim Malusa 

Phil Rosen 

Cecil Schwalbe 

Brent Sigafus 

Dennis Suhre 

Inventory & Monitoring 

Patricia Guertin 

Bill Halvorson 

Brian Powell 

Cecilia Schmidt 

Vegetation Mapping & Ecology 

Patricia Guertin 

Bill Halvorson 

Jim Malusa

Dennis Suhre

USGS Southwest Biological Science Center http://sbsc.wr.usgs.gov
iv 

Table of Contents 

Executive Summary ......................................................................................................................................1

Introduction and Definitions .........................................................................................................................1

Behavioral Adaptations ............................................................................................................................2

Morphological Adaptations ......................................................................................................................3

Physiological Adaptations ........................................................................................................................4

Methods for Studying Water Physiology......................................................................................................9

Water Balance and Water Flux.................................................................................................................9

Blood Constituents .................................................................................................................................10

Water Loss..............................................................................................................................................10

Literature Cited ...........................................................................................................................................11

Annotated Biblography...............................................................................................................................19

Ungulate Mammals ................................................................................................................................19

Marsupial Mammals...............................................................................................................................86

Small Eutherian Mammals .....................................................................................................................92

Techniques and Methodology ..............................................................................................................108

General Desert Ecophysiology .............................................................................................................110

Acknowledgements 

This study was funded and supported by the Arizona Game and Fish Department, Research Branch and 

the School of Natural Resources, The University of Arizona. 
1 

Executive Summary

Ungulates adapted to desert areas are able to 

survive extreme temperatures and limited water 

availability. This ability is largely due to 

behavioral, morphological, and physiological 

adaptations that allow these animals to avoid or 

tolerate extreme environmental conditions. The 

physiological adaptations possessed by ungulates 

for thermoregulation and maintenance of water 

balance have been the subject of numerous studies 

involving a wide range of species. In this report 

we review the behavioral, morphological, and 

physiological mechanisms used by ungulates and 

other desert mammals to maintain water and 

temperature balance in arid environments. We 

also review some of the more commonly used 

methods for studying the physiological 

mechanisms involved in water balance and 

thermoregulation, and the influence of 

dehydration on these mechanisms. 

Introduction and Definitions 

For this literature review and annotated 

bibliography our objectives were (1) to compile 

available scientific literature on thermoregulation 

and water balance in desert mammals, particularly 

studies on ungulates and (2) to review the 

methodologies available to study the 

physiological mechanisms involved in 

thermoregulation and water balance. We were 

specifically interested in the physiological 

responses of ungulates to dehydration. This 

overview and annotated bibliography are intended 

as a source of references for wildlife biologists, 

wildlife managers, and others interested in 

wildlife who have a modest amount of knowledge 

and experience with animal physiology. 

At the outset, it is necessary to define water 

balance and water flux because they commonly 

appear in the literature contained in this 

bibliography. Water balance is the condition 

where intake of free water, preformed water in 

food, and metabolic water equals water loss 

through feces, urine, and cutaneous and 

pulmonary evaporation over a specific period of 

time (Louw 1993). Animals may experience 

positive or negative water balance at a given point 

in time. Water flux or water turnover is the 

amount of water (ml/day) an animal processes 

through its body each day (Nagy and Peterson 

1988). 

We review literature relating to the effects of 

dehydration on wild and domestic ungulates and 

also discuss the behavioral, morphological, and 

physiological mechanisms used by ungulates to 

maintain water and temperature balance in an arid 

environment: 

 Behavioral adaptations reviewed include 

timing of activities, use of microhabitats, 

body orientation, migration, diet selection, 

and social behaviors. 

 Morphological adaptations include body size 

and shape, pelage and skin characteristics, and 

patterns of fat deposition. 

 Physiological adaptations include adaptive 

heterothermy and selective brain cooling, as 

well as adjustments to metabolic rate, renal 

and digestive water loss, and pulmonary and 

cutaneous evaporative water loss. 

Finally, we review some commonly used methods 

for the study of the physiological mechanisms 

involved in water balance and thermoregulation, 

and the influence of dehydration on these 

mechanisms. We have included some studies 

conducted on the physiology of thermoregulation 

and water balance on small eutherian and 

marsupial mammals. 

Adaptations for Thermoregulation and 

Maintenance of Water Balance 

The physiological adaptations possessed by 

ungulates for thermoregulation and maintenance 

of water balance have been investigated using a 

variety of methods in domestic goats, sheep, 

horses, donkeys (Equus asinus), cattle, camels 

(Camelus dromedarius), guanacos (Llama 

guanicoe), llamas (Llama glama), cervids (deer 

[Odocoileus spp.] and elk [Cervus elaphus]), 

pronghorn (Antilocapra americana), desert 

bighorn sheep (Ovis canadensis mexicana and O. 

c. nelsoni), reindeer (Rangifer tarandus), 
2 

muskoxen (Ovibos moschatus), and a wide range 

of African gazelles and other bovids. 

Ungulates adapted to desert areas are able to 

survive and even thrive, despite extreme 

temperatures and scarce water, by (1) avoiding 

environmental conditions that can result in heat 

stress and dehydration or (2) tolerating these 

conditions using behavioral, morphological, and 

physiological adaptations. (Schmidt-Nielsen 1979; 

Louw and Seely 1982). 

Behavioral Adaptations 

Desert ungulates reduce heat loads and maintain 

water balance using daily timing of activity, diet 

selection, microhabitats, body orientation, 

migration, seasonal timing of reproduction, and 

social behaviors (Jarman 1977; Berry et al. 1984; 

Skinner and van Jaarsveld 1987; Fryxell and 

Sinclair 1988a; Alderman et al. 1989; Sargeant et 

al. 1994; Costa 1995). Although described 

separately here, behavioral adaptations function in 

combination with both morphological and 

physiological adaptations. 

 

Timing of Activity. Seasonal changes in the 

duration or timing of daily activities can reduce 

heat loads and minimize evaporative water loss. 

During the hottest, driest periods of the year some 

species reduce diurnal activity and become more 

crepuscular, foraging and moving during the 

cooler periods of the day and thereby reducing 

daily heat loads (Jarman 1977; Alderman et al. 

1989; Vrahimis and Kok 1992; Hayes and 

Krausman 1993; Sargeant et al. 1994). Nocturnal 

activities, including feeding have been 

documented for cattle, pronghorn (Ellis and 

Travis 1975; Lewis 1977), oryx (Oryx beisa), 

eland (Taurotragus oryx), African buffalo 

(Syncerus caffer – Lewis 1977), desert bighorn 

sheep (Miller et al. 1984), and desert mule deer 

(Odocoileus hemionus eremicus – Hayes and 

Krausman 1993). 

In addition to the thermoregulatory benefits of 

restricting activities to cooler nighttime periods, 

ungulates in some areas also increase the intake of 

preformed water by foraging at night. In areas 

where relative humidity increases at night, plants 

absorb moisture from the cool night air, thereby 

increasing preformed water content of forage 

(Taylor 1969a). For example, in northern Kenya, 

the Namib Desert, and Aldabra Atoll in the 

Seychelles Islands, as ambient temperatures 

decrease at night, the air loses its capacity to hold 

water and excess condensates on vegetation 

(Taylor 1968a, 1969a, 1972; Burke 1988). 

Nocturnal feeding in these areas can provide 

animals with forage containing up to 40% more 

water than is available in these same plant species 

during the day (Taylor 1968a, 1969a). 

Furthermore, the general behavior of selecting 

forage plants with higher moisture content, 

regardless of time of day, may provide a means to 

reduce the amount of free water needed to 

maintain water balance (Taylor 1969a; Carlisle 

and Ghobial 1968: Jarman 1973). 

Use of Microclimates. The use of cooler 

microclimates also reduces heat loads and the 

need for evaporative cooling, thus conserving 

water. Use of shaded, lower temperature 

microhabitat is a common behavior during midday 

when temperatures are highest, and has been 

observed in a variety of wild ungulates, including 

dik-dik (Rhynchotragus kirkii – Kamau and 

Maloiy 1985), desert bighorn sheep (Simmons 

1969; Hansen 1982), desert mule deer (Sargeant et 

al. 1994; Tull et al. 2001), collared peccary 

(Pecari tajacu – Sowls 1997), dorcas gazelle 

(Gazella dorcas – Wilson 1989), eland (Taylor 

and Lyman 1967), oryx (Lewis 1978), springbok 

(Antidorcas marsupialis – Bigalke 1972; Hofmeyr 

and Louw 1987), domestic cattle (Lewis 1978), 

and sheep (Johnson and Strack 1992). 

Ungulates that are active during the hotter periods 

of the day and those that inhabit areas lacking 

shade are able to reduce the amount of solar 

radiation absorbed by adjusting body position 

relative to the location of the sun (Taylor 1969a; 

Berry et al. 1984; Hofmeyr and Louw 1987; 

Vrahimis and Kok 1992). To minimize heat gain 

and water loss, animals in shadeless areas stand 

with the long axis of the body parallel to the 

direction of the sun with the rump pointed towards 

the sun or lie down in this position with head 

down, shaded by their body, thereby reducing 

solar radiation loads (Jarman 1977; Berry et al. 
3 

1984; Hofmeyr and Louw 1987; Vrahimis and 

Kok 1992). For example, springbok using this 

body orientation can reduce estimated solar 

radiation load by 62% during the day (Hofmeyr 

and Louw 1987). Social interactions also facilitate 

reduction of heat loads. For example, camels 

(Wilson 1990) and collared peccaries (Sowls 

1997) create shade for each other and reduce the 

amount of surface area exposed to solar radiation 

by bedding down in small groups. 

Migration. Migration is also used by some species 

to avoid high temperatures, limited water 

availability, and poor forage conditions. Ungulate 

species that currently have or had migratory 

populations, include eland, gazelles, gemsbok 

(Oryx gazella), springbok, wildebeest 

(Connochaetes taurinus), elephant (Loxodonta 

africana), and zebra (Equus spp.) in Africa; elk, 

pronghorn, bison (Bison bison), mule deer, and 

caribou in North America; and chamois 

(Rupicapra rupicapra), saiga (Saiga tatarica), 

Mongolian gazelle (Procapra gutturosa), and 

Tibetan antelope (Pantholops hodgsoni) in Europe 

and Asia (Grzimek and Grzimek 1960; Field 

1971; Talbot and Talbot 1978; Fryxell and 

Sinclair 1988a). While ungulates in different areas 

show varying patterns of migration, some migrate 

across the landscape (e.g., wildebeest). and others 

migrate altitudinally (e.g., elk). Quantity and 

quality of forage resources, avoidance of 

predation, and availability of drinking water may 

be reasons to vary migration patterns (Fryxell and 

Sinclair 1988a; Rautenstrauch and Krausman 

1989). Ungulates commonly move to areas of 

recent rainfall to take advantage of the increasing 

quantity and or quality of vegetation and leave 

areas when drought conditions prevail (Sinclair 

and Fryxell 1985; Fryxell and Sinclair 1988b). 

Species inhabiting arid or semi-arid environments 

may also respond to changes in the availability of 

surface water (Western 1975; Sinclair and Fryxell 

1985; Fryxell and Sinclair 1988b). 

Timing of Reproduction. Reproduction in 

ungulates is timed to insure that parturition occurs 

at a favorable time of year thus increasing the 

likelihood of offspring survival (Skinner and van 

Jaarsveld 1987). The predictable seasonal 

environmental conditions in temperate and mesic 

tropical areas favors regular seasonal breeding in 

ungulates, with young being born over a relatively 

short time period (Skinner and van Jaarsveld 

1987). Conversely, species that inhabit arid and 

semi-arid areas with unpredictable environmental 

conditions display a more opportunistic breeding 

pattern, where young are born over a more 

extended period of time (Skinner and van 

Jaarsveld 1987). For example, the young of 

springbok (Skinner and Louw 1996; Skinner and 

van Jaarsveld 1987), gemsbok and eland in Africa 

(Skinner and van Jaarsveld 1997), and desert 

bighorn sheep in North America (Thompson and 

Turner 1982; Witham 1983), can be born almost 

any month of the year. 

Morphological Adaptations 

Desert-adapted ungulates possess a variety of 

morphological adaptations that aid in the 

reduction of heat loads and minimize water loss. 

Morphological adaptations that reduce heat loads 

and minimize water loss include body size and 

shape, pelage and skin characteristics, and 

patterns of fat deposition (Louw and Seely 1982). 

Although described separately here, 

morphological adaptations to life in arid areas do 

not function in isolation, but work in combination 

with both physiological and behavioral 

adaptations. 

Body Size and Shape. Major morphological 

characteristics that regulate heat gain and water 

loss in ungulates are body size and shape. Large 

bodied animals gain heat from the environment at 

a slower rate than do smaller animals because they 

have a lower surface-area-to-volume ratio and 

higher thermal inertia (Scholander et al. 1950; 

Herreid and Kessel 1967; McNab 1983; Bradley 

and Deavers 1980; Phillips and Heath 1995). The 

relatively small surface area of large animals 

reduces the proportion of the animal exposed to 

solar radiation, thereby reducing potential 

environmental heat loads. 

Although their overall energy requirements are 

higher, large animals also have lower massspecific metabolic rates than do small animals; 

these low metabolic rates contribute relatively less 

metabolic heat to the total heat load (Kleiber 

1932; Schmidt-Nielsen 1979; Louw and Seely 
4 

1982). While having a large body reduces the rate 

at which heat is gained from the environment, it is 

disadvantageous because it also reduces the rate 

of heat loss to the environment and shaded 

microclimates of sufficient size are often more 

limited in areas that are sparsely vegetated or lack 

other types of cover (Louw and Seely 1982). 

The shape of the body and appendages also 

influences the rates of heat gain and loss in 

animals; thin appendages minimize radiant heat 

gain and maximize convective heat loss (Louw 

1993). Compared to similar species inhabiting 

mesic areas, desert-adapted species often have 

longer, thinner appendages with a higher surfaceto-volume ratio that facilitates heat loss (Bradley 

and Deavers 1980; Philips and Heath 1992). 

Changes in the rate of blood flow from the body 

core to the surface by vasodilatation and 

vasoconstriction affects the rate of heat loss from 

the body surface. Thus, areas of the body surface 

where the changes in blood flow occur are 

analogous to windows that can be opened or 

closed to regulate heat loss (Philips and Heath 

1992; de Lamo et al. 1998). The highly 

vascularized horns of bovids may have a 

thermoregulatory function (Taylor 1966; Picard et 

al. 1996, 1999). Bovid species from arid areas 

have relatively larger horn cores and thinner 

keratin sheaths than temperate species (Picard et 

al. 1999). Both the thin keratin sheath and larger, 

vascularized horn core would facilitate heat loss 

from horns of tropical bovids compared to 

temperate species (Picard et al. 1996, 1999). 

Pelage Characteristics. Pelage also affects the 

maintenance of heat and water balances in 

ungulates. Both the thickness and color of the 

pelage affect heat transfer between the body and 

the environment (Hofmeyr 1985). Pelage 

thickness affects heat gain and loss of an animal 

from the environment; thin pelage allows more 

heat to reach the body, whereas thick pelage 

provides maximum insulation from solar 

radiation. However, thick coats limit the use of 

sweating for evaporative cooling (Hofmeyr 1985). 

Conversely, thin pelage allows for maximum heat 

loss but provides relatively little insulation. 

There is a decrease in pelage thickness as body 

size increases in desert-adapted ungulates, which 

may facilitate heat loss and compensate for the 

disadvantage of large body size (Hofmeyr 1985; 

Hofmeyr and Louw 1987). Pelage color also 

affects rates of heat gain and loss. Desert-adapted 

ungulates are typically light colored. Light 

colored pelage reflects more radiation than does 

dark colored pelage (Hofmeyr 1985). However, 

while dark colored pelage may absorb more solar 

radiation than light colored pelage, reduced 

radiation reaches the skin of the animal, and 

animals with dark pelage (e.g., black Bedouin 

goats – Shkolnik et al. 1972) can have lower 

metabolic rates in winter than animals with light 

colored pelages (Louw and Seely 1982; Louw 

1993). 

Fat Deposition. The location of fat deposition also 

affects rates of heat loss and gain. Fat stored 

subcutaneously throughout the body may inhibit 

the loss of heat to the environment (Louw and 

Seely 1982). The storage of fat in localized areas 

may be an adaptation to reduce the impact of fat 

reserves on an animal’s ability to lose heat to the 

environment by minimizing the insulative effect 

of fat to small areas of the body, thus facilitating 

heat lost over other body surfaces. Examples of 

animals that have highly localized fat storage 

include the camel, zebu cattle, and arid–adapted 

fat-tailed sheep (Degen 1977c; Louw and Seely 

1982; Wilson 1989). 

Physiological Adaptations 

Physiological adaptations function to minimize 

cutaneous and pulmonary water loss and water 

loss in feces and urine. Physiological mechanisms 

used by desert ungulates to minimize water loss 

include adaptive heterothermy, changes in 

metabolic rate, reduction in renal and digestive 

water loss, and reduction in pulmonary 

evaporative water loss by cooling exhaled air 

(Louw and Seely 1982; McNab 2002). 

Water Loss. There are four primary routes of 

water loss in mammals: cutaneous and pulmonary 

evaporation, feces, and urine. Lactation is an 

additional route of water loss for females nursing 

young. Desert-adapted ungulates have evolved 

physiological adaptations that reduce the amount 

of water lost through each of these routes or are 
5 

able to tolerate significant amounts water loss. 

Some species (e.g., camels and Bedouin goats) 

can survive water losses amounting to 30 – 40% 

of body mass, whereas in others (e.g., waterbuck) 

a 15% loss can result in mortality (Taylor et al. 

1969b; Louw 1984). 

Desert-adapted ungulates employ facultative use 

of cutaneous evaporation, depending on their 

extent of hydration. Cutaneous evaporation 

involves both insensible water loss (water loss 

from moist surfaces) and sensible water loss (i.e., 

sweating). The latter is controlled by a neural 

response to heat. In hydrated animals, the rate of 

cutaneous evaporation generally increases with 

body temperature. However, when dehydrated, 

Grant’s gazelle (Gazella granti), Thomson’s 

gazelle (Gazella thompsonii), oryx, eland, 

wildebeest, hartebeest, African buffalo, zebu steer 

(Taylor 1969a, 1970a, b), impala (Aepyceros 

melampus – Maloiy and Hopcraft 1971), east 

African goat (Schoen 1968), donkey (Maloiy 

1970), and camel (Schmidt-Nielsen et al. 1957) 

reduce the rate of cutaneous evaporation. 

Cutaneous evaporation rates of hydrated animals 

declined by 12 – 89% when dehydrated. The body 

temperature at which dehydrated animals begin 

sweating is often higher than that of normally 

hydrated animals (Schmidt-Nielsen et al. 1957; 

Taylor 1969a, 1970a, b). At very high ambient 

temperatures (45 oC), species such as the oryx 

stop sweating entirely, with the exception of 

insensible water loss from the skin, and use 

adaptive heterothermy (see below) to reduce 

evaporative water loss (Schmidt-Nielsen et al 

1957; Taylor 1969a, 1970a, b). 

Pulmonary evaporation is another major avenue of 

water loss in mammals. Similar to the rates of 

cutaneous evaporation, pulmonary evaporation 

tends to increase with increasing body 

temperature. In normally hydrated animals, 

respiratory rates increase with increasing ambient 

temperature, resulting in increased rates of 

pulmonary evaporation (Taylor 1969b, 1970a; 

Maloiy and Hopcraft 1971; Finch 1972). 

Dehydrated animals often have lower respiratory 

rates and initiate panting at higher ambient 

temperatures than do normally hydrated animals. 

However, some species (e.g. dik-dik and 

wildebeest) increase respiratory rates with 

increasing ambient temperature regardless of their 

water status (Taylor 1969a, 1970a, b; Maloiy 

1973a). By breathing slowly and deeply some 

ungulates may be able to extract more oxygen per 

breath, therefore reducing the amount of air 

needed to move through the lungs and thus 

reducing respiratory water loss (Taylor 1969a). 

Another mechanism that can result in the 

reduction of water loss via pulmonary evaporation 

is the reduction in water content of expired air. 

Expired air is cooled as it passes over the 

relatively cool nasal turbinates, allowing 

extraction of water and reducing respiratory water 

loss (Taylor 1969a; Langman et al. 1978, 1979; 

Schmidt-Nielsen et al. 1981a, b). 

Reduction in water content of feces and urine, and 

increases in urine osmolality are mechanisms by 

which ungulates reduce water loss (Maloiy et al. 

1979). Considerable interspecific variation in the 

moisture content of feces exists in normallyhydrated ungulates. Fecal water content ranges 

from 40- 50% in arid-adapted species (e.g., 

springbok, gemsbok) to 70-80% in species 

adapted to more mesic areas (e.g., cattle, 

waterbuck [Kobus ellipsiprymnus] – Maloiy et al. 

1979; Louw and Seely 1982; Woodall et al. 1999). 

Reductions in fecal moisture content of 17-50% 

have been found in some ungulates (e.g., dorcas 

gazelle, eland, cattle, camel, impala, desert 

bighorn sheep) when dehydrated (Ghobrial and 

Cloudsley-Thompson 1966; Taylor and Lyman 

1967; Maloiy and Hopcraft 1971; Turner 1973). 

Water is reabsorbed in the colon, and species 

possessing large intestines that are longer and 

have more surface area with smaller 

circumferences of the proximal and distal colon 

are able to produce drier feces (e.g., springbok, 

eland, impala versus wildebeest, waterbuck---

Woodall and Skinner 1993). 

Arid-adapted ungulates typically have reduced 

urine output and greater urine concentration than 

do non arid-adapted species (Louw and Seely 

1982). Reductions in urine volume are the result 

of reduced glomerular filtration rates and renal 

plasma flow (Siebert and Macfarlane 1971; 

Maloiy et al. 1979; Wilson 1989). The ability of 

the mammalian kidney to produce hyperosmotic 

urine relative to the blood is related to the length 

of the loop of Henlé in the nephron; mammals 
6 

with longer loops of Henlé are capable of 

producing a more concentrated urine (Louw and 

Seely 1982; McNab 2002). Arid-adapted 

mammals, which produce more concentrated 

urine, have longer loops of Henlé than do other 

species (Schmidt-Nielsen and O’Dell 1961). 

Because most of the loop of Henlé is in the 

medulla of the kidney, the thickness of the 

medulla is correlated with the length of the loop 

of Henlé. The thickness of the medulla relative to 

kidney size, called the relative medullary 

thickness, is often used as an index of kidney 

concentrating ability and is correlated with the 

environment and diet of the animal (Zervanos 

2002; McNab 2002). In desert bighorn sheep, the 

relative medullary thickness is nearly twice that of 

domestic sheep and urine concentrations of 3,900 

mosm have been measured (Horst and 

Langworthy 1971; Turner 1973). 

Water is conserved when dehydrated ungulates 

reduce total urine volume and increase 

concentration (Taylor and Lyman 1967; Schoen 

1969; Maloiy and Hopcraft 1971; Maloiy et al. 

1979; Ali et al. 1982; Mohamed et al. 1988). 

Reductions in urine volume ranging from 0 to 

76% and increases in urine osmolality ranging 

from 3 to 239% have been documented in 

comparisons of normally hydrated and dehydrated 

ungulates (e.g., camels, goats, sheep, dorcas 

gazelle, Grant’s gazelle, Thomson’s gazelle, and 

rock hyrax – Taylor et al. 1969a; Khan et al. 

1978; Maloiy et al. 1979; Ali et al. 1982; Olsson 

et al. 1982; Etzion and Yagil 1986; Mohamed et 

al. 1988; Wilson 1989). 

Role of the Rumen in Water Balance. The 

relatively large volume of fluid in the alimentary 

tract of ruminants may maintain water balance for 

blood and body tissues for the first few days of 

water deprivation (Hecker et al. 1964, Maloiy et 

al. 1979, Louw and Seely 1982). After 

dehydration, some desert-adapted species are able 

to drink water in amounts equivalent to a large 

proportion of their body mass. For example, 

Bedouin goats (Choshniak and Shkolnik 1977), 

donkey (Maloiy 1970), camels (Schmidt-Nielsen 

1979), and desert bighorn sheep (Turner 1973) are 

able to drink water in amounts equivalent to 40, 

30, 30, and 20% of their body mass, respectively. 

However, other species, such as oxen and cattle, 

are not able to rapidly imbibe water because of 

problems associated with hemolysis (Bianca 

1970; Louw 1984). 

The function of the rumen during rehydration 

differs among species that are able to ingest large 

volumes of water over short time periods. For 

example, in camels, water ingested rapidly passes 

from the alimentary tract to the blood and body 

tissues (Schmidt-Nielsen 1979; Etzion et al. 

1984). In desert-adapted goats, large volumes of 

rapidly ingested water are released more slowly to 

the blood and other body tissues, thus minimizing 

hemolysis and osmotic shock to tissues 

(Choshniak and Shkolnik 1977; Louw 1984). 

Osmotic fragility of red blood cells decreases and 

life span of red blood cells increases in some 

ungulates (e.g., camel and desert bighorn sheep) 

when dehydrated (Yagil et al. 1974; Turner 1979). 

Those mechanisms may reduce water 

requirements by minimizing the need to replace 

red blood cells more often; they allow for rapid 

rehydration while minimizing hemolysis (Yagil et 

al. 1974; Turner 1979). 

Body Water Pools And Water Turnover. Total 

body water of mammals is often viewed as being 

composed of separate compartments: the 

intracellular fluid consisting of fluid within cells 

and the extracellular fluid consisting of rumen 

fluid, blood plasma fluid and interstitial fluids; 

water can move between body fluid compartments 

(Lockwood 1966; Maloiy et al. 1979; Louw 

1993). The relative distribution of water and the 

contribution to total fluid loss during dehydration 

varies for each compartment depending on species 

and state of hydration (Maloiy et al. 1979; Louw 

1993). The loss of water from water 

compartments varies for dehydrated animals. 

Ungulates (e.g., camels, Bedouin goats) that are 

able to withstand severe dehydration (i.e., 20 – 

30% of body mass) typically lose relatively less 

water from blood plasma fluid than from other 

compartments, or are able to move fluid from 

other compartments to maintain plasma volume at 

a level that prevents circulatory failure during 

dehydration (Macfarlane et al. 1961; Yousef et al. 

1970; Choshniak and Shkolnik 1977; Turner 

1979; Choshniak et al. 1984). During the first few 

days of dehydration, fluid contained in the rumen 

provides a large portion of the water lost, and may 
7 

buffer ungulates against short-term water 

deprivation (Hecker et al. 1964; Hoppe et al. 

1975; Maloiy et al. 1979; Turner 1979). 

Water turnover rates vary among species and are 

lower in animals from arid areas than those 

adapted to more mesic conditions; this trend is 

also observed in domestic ungulates with breeds 

adapted to arid areas having lower water turnover 

rates than European breeds (Macfarlane et al. 

1971; Macfarlane and Howard 1972; Degen 

1977a; Maloiy et al. 1979; Nagy and Peterson 

1988). In normally hydrated ungulates (both wild 

and domestic), water turnover rates increase with 

increasing temperature and are lower in winter 

than in summer (e.g., mule deer [1,750 – 8,050 

ml/day – Longhurst et al. 1970; Nagy and 

Peterson 1988], pronghorn [1,940 – 2,420 ml/day 

– Wesley et al. 1970], camel [Siebert and 

Macfarlane 1971; Yousef 1971], feral burro 

[Tomkiewicz 1979], collared peccary [1,170 – 

1,360 ml/day – Zervanos and Day 1977], desert 

bighorn sheep [4,850 – 7,010 ml/day], horse, and 

cattle – Macfarlane and Howard 1972). 

In arctic areas, water availability is limited more 

in winter than in summer resulting in higher water 

turnover rates in arctic ungulates (e.g., caribou, 

muskoxen) in summer than in winter (Cameron 

and Luick 1972; Cameron et al. 1982). When 

ungulates are dehydrated, water turnover rates 

decrease regardless of ambient temperature 

(Maloiy 1973b). Those rates have also been found 

to differ between captive and free-living animals 

of the same species (Nagy and Peterson 1988). 

For example, captive mule deer have significantly 

lower water turnover rates than do free-living 

mule deer (Nagy and Peterson 1988; Parker et al. 

1993). 

Water turnover rates also vary with reproductive 

status. Water turnover rates are 40 – 50% higher 

in pregnant and lactating animals than in 

nonlactating animals (Siebert and Macfarlane 

1971; Macfarlane and Howard 1972; Degen 

1977b; Maloiy et al. 1979; Hassan et al. 1988). 

Water deprivation during lactation can decrease 

milk production (Maltz and Shkolnik 1980; 

Wilson 1989; Hossaini-Hilali et al. 1994). 

Dehydration during lactation can also result in a 

reduction in the concentration of fat and nonfat 

solids and an increase in water content of milk. 

This composition change is viewed as an 

adaptation to insure that nursing young receive 

adequate water during times of limited water 

availability (Mittal 1980; Yagil and Etzion 1980a, 

b; Yagil et al. 1986). 

Maloiy et al. (1979) classified ungulates into three 

functional groups based on water turnover rate, 

metabolic rate, and renal concentrating ability. 

African buffalo, cattle, pig, waterbuck with 

increased rates of water turnover and metabolism 

and poor renal concentrating ability comprise 

Group I; sheep, wildebeest, hyrax [Procavia 

habessinica], donkey with intermediate water 

turnover and metabolic rates and moderate renal 

concentrating abilities comprise Group II; and 

camel, goat, oryx, gazelles that have lower 

metabolic and water turnover rates and higher 

renal concentrating abilities comprise Group III. 

Blood Plasma Constituents. Reductions in plasma 

fluid volume caused by dehydration affect blood 

constituents. The reduction in plasma volume 

results in an overall increase in plasma osmolality 

due to increases in plasma Na+

, Cl-, K+, chloride, 

urea, packed cell volume, hemocrit, and 

hemoglobin concentrations (Bianca et al. 1965; 

Ghobrial and Cloudsley-Thompson 1966; Laden 

et al. 1987; Ben Goumi et al. 1993; Abdelatif and 

Ahmed 1994; Al-Toum and Al-Johany 2000). 

Severe hemoconcentration due to loss of plasma 

fluid can result in death from circulatory failure 

(Schmidt-Nielsen et al. 1956; Macfarlane et al. 

1961). 

Adaptive Heterothermy and Selective Brain 

Cooling. It has been proposed that adaptive 

heterothermy is used by many ungulates in arid 

areas to minimize water loss from evaporative 

cooling (i.e., sweating and panting). By allowing 

the body temperature to rise during the day, 

animals are able to store heat and release it at 

night when ambient temperature falls below the 

body temperature, thus reducing the need to 

dissipate heat during the day via evaporative 

cooling. Normally hydrated desert-adapted 

ungulates with access to free water typically 

maintain body temperature within a fairly narrow 

range by evaporative cooling (Taylor 1970a, b). 

While some species must maintain body 
8 

temperatures within this narrow range regardless 

of their state of hydration, body temperatures of 

some fluctuate over a wider range when 

dehydrated (Taylor et al. 1969a; Finch 1972). 

The larger range over which body temperature 

fluctuates in dehydrated versus hydrated animals 

is often attributed to adaptive heterothermy and its 

water-conserving function (Schmidt-Nielsen et al. 

1957; Taylor 1970a, 1972; Schoen 1972; Taylor 

and Lyman 1972). However, Mitchell et al. 

(2002), in their review of the adaptive 

heterothermy, suggested that the rise in body 

temperature of ungulates observed in previous 

studies was largely an artifact of studying animals 

in captive conditions in which they were 

prevented from employing behavioral and other 

thermoregulatory mechanisms. Furthermore, in 

their studies of free-ranging wildebeest, 

springbok, impala, and oryx, Mitchell et al. (2002) 

failed to find evidence of adaptive heterothermy 

and concluded that increased magnitude of daily 

fluctuations in body temperature observed in 

dehydrated animals was actually dehydrationinduced hyperthermia, not evidence of adaptive 

heterothermy. Dehydration-induced hyperthermia 

may be adaptive in conserving water because it 

results in a increase in the temperature at which 

animals switch from thermoregulation via 

convection and radiation to evaporative cooling 

(Mitchell et al. 2002). 

Selective brain cooling via countercurrent heat 

exchange in the nasal passages is often associated 

with adaptive heterothermy and allows some 

ungulate species to survive body temperatures >42 

oC for long periods of time. The carotid rete is an 

area of the carotid artery divided into a series of 

small blood vessels just below the brain. It comes 

into contact with a network of small veins 

returning from the nasal passages where heat is 

transferred from the warmer arterial blood to the 

venous blood that has been cooled by the animal’s 

respiration when passing through the nasal 

passages (Taylor 1969a; Louw and Seely 1984; 

Wilson 1989). Countercurrent heat exchange can 

result in blood entering the brain ≤ 3.9 oC cooler 

than in the rest of the body (Taylor 1972). 

The carotid rete is not present in all ungulates, but 

has been found in a variety of both arid and nonarid dwelling mammals (e.g., eland, elk). Some 

researchers have concluded that the carotid rete is 

an adaptation to reduce heat in blood going to the 

brain after exercise and consequently provides an 

advantage to animals inhabiting arid areas (Baker 

1979). However, Mitchell et al. (2002) also 

questioned the role of selective brain cooling as a 

mechanism for maintaining the brain at lower 

temperature while body temperature is allowed to 

rise with adaptive heterothermy. They 

hypothesized that selective brain cooling is used 

in free-ranging animals under moderate heat loads 

to switch from evaporative to non-evaporative 

routes, and therefore has a thermoregulatory 

function unrelated to adaptive heterothermy 

(Kuhnen 1997; Mitchell et al.2002). 

Metabolic Rate. Reduction in basal metabolic rate 

(BMR – metabolic rate of resting animal with 

body temperature in thermoneutral zone) can 

minimize metabolic heat gain and reduce water 

loss in ungulates; desert-adapted ungulates often 

have lower metabolic rates than do other 

ungulates (Macfarlane et al. 1971; Shkolnik et al. 

1972; Wilson 1989; Louw 1993). The lower 

metabolic rates of desert-adapted ungulates (e.g., 

camel, Bedouin goat, eland, steenbok [Raphicerus 

campestris]) are associated with lower water 

turnover rates in these animals (Macfarlane and 

Howard 1972; Maloiy et al. 1979). Furthermore, 

dehydrated animals often have lower metabolic 

rates than when normally hydrated (SchmidtNielsen et al. 1967; Taylor 1969a; Finch and King 

1982). 

Diet and Water Balance. The amount of 

preformed water contained in the food of some 

ungulate species (e.g., oryx, Grant’s gazelle, 

springbok) has been associated with free water 

requirements. At times preformed water provides 

a significant portion of the total water intake and 

affects the ability of some species to survive long 

periods without free water (Taylor 1968a, 1969a; 

Schmidt-Nielsen 1979; Zervanos and Kauffman 

1981; Jhala et al. 1992). Dependence on free 

water sources and rates of consumption of forage 

are associated with the moisture content of forage 

(Jarman 1973). The lower moisture content of 

forage used by grazing versus browsing animals 

makes the former more dependent on availability 

of free water (Maloiy 1973a; Kay 1997). 
9 

Dehydration reduces the rate of forage intake (dry 

matter intake) in some ungulate species (e.g., 

white-tailed deer [Lautier et al. 1988], zebu cattle, 

domestic sheep, desert bighorn sheep [Turner 

1973]) whereas others (e.g., arid adapted donkey 

[Maloiy 1970], dorcas gazelle [Mohamed et al. 

1988], bushbuck, reedbuck, Uganda kob [Taylor 

and Maloiy 1967], Bedouin goat [Schoen 1969; 

Chosniak et al. 1988], and camel [Wilson 1989]) 

tend to maintain forge intake even when 

dehydrated. Increases in apparent dry matter 

digestibility have been documented in dehydrated 

ungulates, including Bedouin goats (Silanikove 

1985), cattle (Thornton and Yates 1968), 

Thomson’s and Grant’s gazelles (Maloiy 1973b), 

and desert bighorn sheep (Turner 1973). The 

increase in apparent dry matter digestibility in 

dehydrated ungulates has been associated with 

slower rates of passage of digesta through the 

rumen, thus allowing more time for fermentation 

(Brosh et al. 1983, 1986; Choshniak et al. 1988). 

Methods for Studying Water Physiology 

 

A variety of methods is available for studying 

water physiology in mammals. Methods for 

studying water balance and water flux include 

desiccation and the use of labeled water to 

measure water volume and turnover rate in 

different body water compartments. There are 

different substances available to label water, 

depending on the particular body water 

compartment of interest. Titrated water is 

commonly used to measure total body water, 

inulin and sodium thiocyanate to measure 

extracellular water, and Evan’s blue dye to 

measure blood plasma volume. Inulin is also used 

to measure glomerular filtration rate in studies of 

kidney function. Laboratory tools including 

centrifuges, osmometers, spectrometers, and 

autoanlyzers have been used to study aspects of 

blood and fluid chemistry and osmolality of body 

fluids. Methods for the study of the different 

routes of water loss include the use of metabolic 

chambers and metabolic masks to assess water 

lost via respiration, use of absorbent capsules to 

measure rates of cutaneous water loss, and 

collection of urine and feces to determine water 

loss. 

Water Balance and Water Flux 

Two methods have been used to estimate total 

body water (TBW): desiccation and labeled water. 

The desiccation method involves weighing an 

animal in the state of hydration of interest, killing 

the animal and drying the carcass to a constant 

mass, then estimating total body water by the 

difference in live versus dry mass. The second 

method involves the use of the indicator-dilution 

principle to estimate TBW or water volume in 

individual compartments (Lassiter and Gottschalk 

1980a; Holleman et al. 1982; Guyton and Hall 

1996). Total body water or the volume of an 

individual fluid compartment is determined by 

injecting a known volume and concentration of 

substance that will mix uniformly with the fluid of 

the compartment of interest, then, samples of the 

compartment fluid are taken after the introduced 

fluid equilibrates with the compartment fluid, and 

the concentration of the indicator substance is 

determined. The volume of the compartment can 

be determined by the following equation: 

volume B = 

([volume A]×[concentration A])/concentration B 

where volume B is the compartment volume, 

volume and concentration A are the volume and 

concentration of the indicator substance used, and 

concentration B is the concentration of the 

indicator substance in the fluid of the 

compartment (Guyton and Hall 1996). 

However, because body fluids are constantly 

changing, modifications to the above equation and 

collection of serial samples of the compartment 

fluid are necessary (Lassiter and Gottschalk 

1980a; Guyton and Hall 1996). The rate of the 

disappearance of the indicator substance in the 

body fluid is used to determine TBW flux rate. 

There are six assumptions in the use of titrated 

water to estimate total body water and water flux: 

(1) body water volume does not change during the 

measurement period; (2) water flux rates are 

constant during measurement period; (3) the 

isotope is not incorporated into body constituents 

other than water; (4) the isotope only leaves the 

body in the form of water; (5) concentration of 

isotope in water lost is equal to the concentration 

in body water; and (6) water in the environment 
10 

does not enter the animal via the skin or lungs 

(Holleman et al. 1980; Nagy and Costa 1980). The 

effects of violating those assumptions and 

methods for minimizing related errors are 

described in Nagy and Costa (1980) and Nagy 

(1983). For example, most errors can be 

minimized or avoided by recognizing violations of 

assumptions and using appropriate equations to 

adjust for these violations; water flux rate 

estimates using the titrated water method are 

usually ±10% of actual flux rates (Nagy and Costa 

1980). 

In the past, a variety of substances has been used 

to estimate TBW (e.g., antipyrine, deuterated 

water, and titrated water), extracellular fluid 

volume (ECFV – e.g., inulin, sodium thiocyanate, 

bromide, sucrose, mannitol, radiosulfate), and 

blood plasma volume (e.g., radioiodinated human 

serum albumin, Evan’s blue dye) (Lassiter and 

Gottschalk 1980a; Guyton and Hall 1996). 

Currently, the most common substances used are 

deuterated and titrated water to estimate TBW; 

inulin and sodium thiocyanate to estimate ECFV; 

and Evan’s blue and radioiodinated human serum 

albumin to estimate blood plasma volume 

(Lassiter and Gottschalk 1980a; Guyton and Hall 

1996). Intracellular fluid volume cannot be 

measured directly, but is estimated by the 

difference between total body water and 

extracellular fluid volume (Lassiter and 

Gottschalk 1980a; Guyton and Hall 1996). 

Radio-isotopically labeled water methods are not 

limited to the laboratory or captive animals and 

can be used on free-living animals in natural 

conditions under some circumstances (Nagy 1975, 

1994). Animals must be captured and held briefly 

at least twice—once to administer the labeled 

water, collect baseline samples, and mark the 

animal so that it can be identified later, and at 

least once after the isotopically labeled water 

equilibrates (mixes uniformly) with the fluid of 

the compartment of interest. The equilibrium time 

for titrated water in ungulates varies from 5 – 6 hr 

in sheep and goats, 7 – 8 hr in cattle, and 8 – 12 hr 

in camels (Siebert and Macfarlane 1971; 

Macfarlane and Howard 1972; Holleman et al. 

1982). 

Blood Constituents 

Hemocrit or Packed Cell Volume. Hemocrit or 

packed cell volume is determined by 

centrifugation. Whole blood is centrifuged in 

calibrated tubes to determine the total cell volume 

to total blood volume; calibrated centrifuge tubes 

can be used that allow the direct estimate of 

percent of cells (Lassiter and Gottschalk 1980b; 

Guyton and Hall 1996). 

Blood Osmolality, Sodium, Potassium, and Urea 

Concentration. Blood osmolality is determined 

using an osmometer. Serum sodium (Na+

) and 

potassium (K+

) concentrations are determined 

using flame-photometry. Urea and phosphate 

concentrations are determined using an 

autoanlyzer using sample preparation techniques 

specific to the constituent of interest; preparation 

techniques are provided in Schalm et al. (2000). 

Water Loss 

Pulmonary Water Loss.Water lost during 

respiration can be measured by placing the animal 

in a sealed metabolic cage if animal is small 

enough or by fitting an animal with a metabolic 

mask. The relative humidity of both inspired and 

exhaled air are measured. The absolute water 

content of exhaled air is calculated from the 

relative humidity. Water content of expired air is 

measured either using a humidity sensor or by use 

of a drying agent (e.g., Drierite) to absorb water 

from exhaled air (Taylor 1969b; Borut et al. 1979; 

Schmidt-Nielsen et al. 1981a, b; Dmi’el and 

Robertshaw 1983). 

Cutaneous Water Loss. Cutaneous water loss can 

be estimated by applying a desiccant capsule 

containing Drierite to a shaved area of the skin for 

a specific period of time; by weighing the capsule 

before and after application water content can be 

determined and cutaneous evaporation rate 

estimated (Musewe et al. 1976). However, 

differences in sweat gland density over different 

areas of the body and differences in surface area 

must be taken into consideration. Cutaneous water 

loss can also be calculated using total evaporative 

water loss estimated by the body mass lost by an 
11 

animal during an experiment (Borut et al. 1979; 

Taylor et al. 1970a; Dmi’el and Robertshaw 

1983). All mass lost during an experiment is 

assumed to be due to evaporative water loss; 

either the animal cannot urinate or defecate during 

the experiment or all urine and feces need to be 

collected to account for mass lost due to those 

routes (Borut et al. 1979; Taylor et al. 1970a; 

Dmi’el and Robertshaw 1983). Respiratory water 

loss is measured using the above method, and 

total cutaneous water loss is assumed to be the 

difference between the total evaporative water 

loss and the respiratory water loss (Borut et al. 

1979; Taylor et al. 1970a; Dmi’el and Robertshaw 

1983). 

Fecal Moisture Content. Fecal moisture content is 

determined by weighing a fresh sample of feces. 

The sample is then dried at 50 oC to a constant 

mass and reweighed. Moisture content is the 

difference between the fresh and dried mass 

(Woodall et al. 1999). 

Glomerular Filtration Rate and Urine Osmolality.

Glumerular filtration rate (GFR) is the amount of 

filtrate produced per minute by all nephrons in 

both kidneys and is associated with rates of urine 

production (Lassiter and Gottschalk 1980a; 

Guyton and Hall 1996). Inulin is commonly used 

as a marker to measure the GFR in animals 

(Lassiter and Gottschalk 1980a; Guyton and Hall 

1996). Sterile inulin is administered to the animal 

intravenously, serial blood and urine samples are 

collected and the concentration of inulin is 

determined (Lassiter and Gottschalk 1980a). 

Because inulin is freely filterable in the 

glomerulus and it is neither reabsorbed nor 

secreted by the renal tubules, the amount excreted 

is equal to the amount filtered. Therefore, the 

glomerular filtration rate can be calculated using 

the following equation: 

Glomerular filtration rate = (Ux V)/Px, 

where Ux is concentration of inulin in the urine, V 

is the rate of urine flow, and Px is the inulin 

concentration of the plasma (Lassiter and 

Gottschalk 1980a). 

Urine osmolality is measured using an osmometer 

(Maloiy 1973a). 

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The annotation for each citation is in most cases 

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Blood was collected and analyzed during 3 phases 
20 

of experimentation; hydrated, dehydrated and 

rehydrated. The gazelle’s dehydration led to an 

increase in many of blood parameters such as red 

blood cells, white blood cells, packed cell volume, 

amount of hemoglobin, serum Na+

 and Cl-, blood 

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mass was 54.6 ± 1.8. The biological half-life was 

5.4 ± 0.4 days. Smaller variations were observed 

between individual sheep than reported by 

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72.7 ml kg-1 and the daily intake and urine 

production were 66.8 and 27.1 ml kg-1, 

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The effects of environmental temperature in feed 

digestion, water metabolism, body temperature 

and certain blood characteristics of sheep were 

investigated. In each of 4 periods, domestic sheep 

were maintained at 20 oC for 1 week, at -11 oC for 

the following week, and at 20 oC again for the 

third week. In one period, water intake was 

voluntary; in the other 3 periods the sheep 

received either 1,000, 2,000, or 3, 000 g water 

day-1 through rumen fistulas. The change from the 

warm to the cold occasioned no change in feed 

digestibility but when the sheep were returned to 

the warm, the apparent digestion of both dry 

matter and fiber increased. When water intake was 

voluntary, water consumption, urine water loss, 

and apparent insensible water loss were lower in 

the cold than in the warm temperatures. During 

the second week at 20 oC, the apparent insensible 

water loss was higher than during the first week at 

20 oC. When water intake was controlled at three 

different levels, urine and fecal water losses 

tended to reflect the differences in water intake. 

Temperatures in the rectum and subcutaneous 

tissues exhibited a decrease when the sheep were 

transferred from warm to cold and a transient 

increase on return to the warm. When water intake 

was voluntary or 1,000 g day-1, transfer of the 

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Measurements of brain and central blood 

temperature (Tbr and Tbl),metabolic rate (MR) and 

respiratory evaporative heat loss (REHL) were 

made in trained goats walking on a treadmill at 4.8 

km h-1 at treadmill inclines of 0, 5, 10, 15 and 20% 

when they were fully hydrated and at 0% when 

they had been deprived of water for 72 h. In 

hydrated goats, exercise MRincreased 

progressively with increasing treadmill incline. 

Both Tbl and Tbr rose during exercise, but Tbl

always rose more than Tbr, and selective brain 

cooling (SBC = Tbl - Tbr) increased linearly with 

Tbl. Significant linear relationships were also 

present between REHL and Tbl and between SBC

and REHL. Neither the slope of the regression 

relating SBC to Tbl nor the threshold Tbl for onset 

of SBC was affected by exercise intensity. Manual

occlusion of the angularis oculi veins decreased 

SBC in a walking goat, while occlusion of the 

facial veins increased SBC. Dehydrated goats had

higher levels of Tbl, Tbr and SBC during exercise, 

but the relationship between SBC and Tbl was the 

same in hydrated and dehydrated animals. In

dehydrated animals, REHL at a given Tbl was 

lower and SBC was thus maintained at reduced 

rates of REHL. It is concluded that SBC is a linear 

function of body core temperature in exercising 

goats and REHL appears to be a major factor 
21 

underlying SBC in exercise. The maintenance of

SBC in spite of reduced REHL in dehydrated 

animals could be a consequence of increased 

vascular resistance in the facial vein and increased 

flow of cool nasal venous blood into the cranial 

cavity. 

Banerjee, S. and R. C. Bhattacharjee. 1963. 

Distribution of body water in the camel (Camelus 

dromedarius). American Journal of Physiology 

204:1045-1047. 

The distribution of body water in the different 

compartments were determined in adult male 

Indian camels with one hump. The average 

distributions were as follows: serum volume, 

5.9% of body mass; blood volume, 8.3% of body 

weight; total body water (urea space), 68.7% of 

body mass; extracellular water (thiocyanate 

space), 23.3% of body mass; intracellular water, 

45.5% of body mass; and interstitial water, 17.4% 

of body mass. The serum and blood volumes of 

the camel were higher than similar values in other 

ruminants. When these values were compared 

with similar values in man, it was observed that 

the camel had significantly higher serum volumes, 

total body water, and intracellular water volumes. 

The capacity of the camel to hold more water 

might help the animal in withstanding the 

deprivation of water for a prolonged period in 

comparison to other animals. 

Barboza, P. S., J. E. Blake, and R. E. Haugerud. 1999. 

Rangifer bulls in rut: body composition and water 

kinetics. Scientific and Social Programme Abstracts10th Arctic Ungulate Conference, University of Tromso, 

Tromso, Norway. 

Rut is a metabolically demanding period for male 

ruminants. Bulls must fight, patrol harems and 

mark territories as well as maintain and repair 

their body tissues. Seven adult male (Rangifer 

tarandus tarandus) were studies in 2 herds with a 

total of 34 females. Bulls became aggressive to 

handlers in late August when the antler velvet was 

shed. Plasma testosterone was greater in early 

September (246 day; 2,128 nag dL-1) than in either 

June (176 day; 12 nag dL-1) or October (301 day; 

83 nag dL-1). Subordinate males lost mass 

between September and November in a similar 

pattern to the dominant harem males. Peak mass 

and the date of peak mass did not vary with status 

or age in males 2 yr and older (P>0.05). Two bulls 

died in September from infected wounds. 

Surviving animals did not recover mass in winter 

suggesting that both injury and low body reserves 

can cause mortality. Titrated water dilution space 

declined with body mass. High rates of water flux 

in August probably reflect intakes of both food 

and drinking water to support mass gains and 

losses to panting for thermoregulation. Low water 

fluxes at the end of the rut may indicate low 

intakes of food and renal conservation when snow 

is the only source of free water. Animals lost 35% 

of the ingesta-free mass in 77 d of rut. Lean mass 

and body protein were depleted by 23% whereas 

78% of the fat reserve was expended. Daily losses 

of protein and fat were 77 g and 437 g 

respectively which corresponded to a loss of 

19MJ day-1 of 63% of body energy during rut. The 

daily energy deficit was equivalent to 90% of the 

standard metabolic rate. Body reserves probably 

provide sufficient energy for basal metabolism but 

additional costs of activity and thermoregulation 

must be supported by food intake. 

Benga, G. and T. Borza. 1995. Diffusional water 

permeability of mammalian red blood cells. 

Comparative Biochemistry and Physiology 112B:653-

659. 

A program of comparative nuclear magnetic 

resonance measurements of the membrane 

diffusional permeability for water and of the 

activation energy of this process in red blood cells 

from 21 mammalian species was conducted. On 

the basis of diffusional permeability for water 

these species could be divided into three groups. 

First, the red blood cells from humans, cow, 

sheep, and large kangaroos (Macropus giganteus

and M. rufus) and diffusional permeability for 

water values around 5 x 10-3 cm s-1 at 25 oC and 7 

x 10-3 cm s-1 at 37 oC. The red blood cells of other 

marsupial species, mouse, rat, guinea pig, and 

rabbit had diffusional permeability for water 

values roughly twice as high, whereas echidna red 

blood cells were half that of human red blood 

cells. The value of activation energy was in most 

cases correlated with the values of diffusional 
22 

permeability for water values. An activation 

energy value of 26 kJ mol-1 was found for red 

blood cells from humans and species having 

similar diffusional permeability values. Low 

activation energy values (ranging from 15 to 22 kJ 

mol-1) appeared to be associated with relatively 

high diffusional permeability values. The highest 

activation energy value (33 kJ mol-1) was found in 

echidna red blood cells. This points to specialized 

channels for water diffusion incorporated in 

membrane proteins; a relatively high water 

permeability of red blood cell membrane could be 

due to a greater number of channel proteins. There 

are, however, situations where a very high water 

permeability of red blood cells is associated with a 

high value of activation energy as is the case of 

red blood cells from mouse, rat, and tree 

kangaroo. It was also found that diffusional 

permeability in different species was positively 

correlated to the red blood cell membrane 

phosphatidylcholine and negatively correlated to 

the sphingomyelin content. This suggests that in 

addition to the number of channel proteins, other 

factors are involved in the water permeability of 

the red blood cell membrane. 

Ben Goumi, M., F. Riad, J. Giry, F. De La Farge, A. 

Safwate, M. Davicco, and J. Barlet. 1993. Hormonal 

control of water and sodium in plasma and urine of 

camels during hydration and dehydration. General and 

Comparative Endocrinology 89:378-386. 

Eight dromedary camels were studied for 24 days 

under controlled conditions (3 days), and during 

water deprivation (14 days) and rehydration (7 

days) in Tadla, Morocco during the summer. 

Blood samples were drawn every 6 hr. During 

dehydration, food intake gradually fell and was 

zero on the last day and animals lost about 30% of 

their body mass. However, most of this reduction 

in weight was attributed to water loss, since body 

mass of the animals returned to control values 

following rehydration. Dehydration was 

associated with a decreased in plasma volume (~ 

42 ± 3%) and a concomitant rise in plasma Na 

concentration (from 1.2 ± 0.2 to 20.0 ± 5.2 ng AL1

ml-1 hr-1), without significantly changed plasma 

concentrations of aldosterone and atrial 

naturiuretic peptide. Dehydration was associated 

with increased urine osmolality (from 952 ± 515 

to 1963 ± 498 mOsm kg-1 water), reduced urine 

production (from 4565 ± 2230 to 817 ± 178 ml 

day-1), and increased Na excretion. Most of these 

parameters returned to control values during 

initial rehydration, except for plasma rennin 

activity, which remained elevated for 7 days, and 

diuresis, which rose to 12773 ± 6707 ml day-1 on 

Day 7 of rehydration. 

Bianca, W., J. D. Findlay, and J. A. McLean. 1965. 

Responses of steers to water restriction. Research in 

Veterinary Science 6:38-55. 

An investigation was made into the effects of 

dehydration on various metabolic and 

thermoregulatory functions of steers held in an 

environmental chamber in both temperate (15 oC) 

and hot (40 oC) environments. During 4 days of 

dehydration at 15 oC decreases occurred in food 

intake, the excretion of feces and urine, 

evaporation, body weight, heat production, 

respiratory ventilation, plasma potassium, and in 

urinary potassium output. At the same time 

increases were found for hemocrit, plasma total 

solids, plasma sodium, plasma chloride and blood 

urea, and in the output of urinary sodium. During 

2 days of dehydration at 40 oC, qualitatively 

similar changes occurred in most of these 

variables. The rapid ingestion of large amounts of 

water at the end of each dehydration period 

caused dramatic but transient changes in many of 

the quantities investigated. Some of these changes 

were related to shivering, which followed 

drinking in the temperate, but not in the hot 

environment. The repayment of the water debt 

accumulated during dehydration occurred very 

rapidly, most of it within the first day of 

rehydration. The restoration to normal of the 

various physiological values deranged by 

dehydration required more than 1 day in most 

instances. There did not seem however, to be 

permanent changes nor any impairment of health 

due to the relatively short period of dehydration. 

The results are discussed in relation to 

mechanisms involved in water balance and 

temperature regulation. 
23 

Bianca, W. 1965. Reviews of the progress of dairy 

science. Section A: Physiology. Cattle in a hot 

environment. Journal of Dairy Research 32:291-345. 

Reviews the physiology and mechanisms 

associated with heat production, evaporative 

cooling, evaporation from respiratory passages, 

water exchange, reproduction, milk production, 

feed intake and the influence of body size on 

cattle living in hot environments. 

Bianca, W. 1970. Effects of dehydration, rehydration, 

and overhydration on the blood and urine of oxen. 

British Veterinary Journal 126:121-132. 

Each of 4 oxen, kept in an environment of 20 oC, 

was subjected to the following 3 treatments, 

deprivation of water for 3 days followed by 

rehydration by drinking, deprivation of water for 3 

days followed by rehydration by infusion of water 

through a rumen cannula, and over-hydration 

brought about by infusion of water into the rumen 

of the normally hydrated animals. Dehydration for 

3 days caused hemoconcentration, which was 

associated with a 34% increase in blood viscosity. 

The hemoconcentration observed was due, in the 

first place, to a loss of water from the plasma, but 

some water was also lost from the red cells, as 

evidenced by increases in mean corpuscular 

hemoglobin concentration and in red cell total 

solids. The osmotic fragility of the red cells, and 

urinary specific gravity were increased. 

Rehydration by drinking produced a cardiac 

acceleration and in most of the blood variables an 

overshoot, i.e. a sharp transient rise over the 

values already elevated as a result of dehydration. 

Since both these responses were absent in 

rehydration by infusion, it was thought that they 

were brought about by the stress of sudden 

drinking following a period of dehydration. After 

rehydration, osmotic fragility remained high for 

several hours. In 2 instances, rehydration by 

drinking led to intravascular hemolysis and 

resulting hemoglobinuria. Overhydration caused a 

marked diuresis and a slight hemoconcentration. 

There were no obvious signs of water 

intoxication, however instances of hemolysis and 

hemoglobinuria occurred. 

Bohra, H. C. and P. K. Ghosh. 1977. Effect of restricted 

water intake during summer on the digestibility of cellwall constituents, nitrogen retention and water excretion 

in Marwari sheep. Journal of Agricultural Science 

89:605-608. 

In May-June 1976, studies were made on the 

effect of 50% reduction in daily water intake 

during summer on food intake, digestibility 

coefficients of the cell-wall constituents (CWC), 

nitrogen retention and water excretion in urine 

and feces in the captive Marwari breed of sheep of 

the Rajasthan Desert, India. Animals were held in 

metabolic cages and feces were collected. The 

water-restricted animals consumed 54 and 42% 

less dry matter and digestible energy respectively 

than normally-watered animals. The digestibility 

coefficients of different CWC were apparently, 

though not significantly, higher in water-restricted 

animals. Throughout the study period, animals of 

both the groups, particularly the water-restricted 

group, remained in negative nitrogen balance. 

Moisture loss through the feces was about 22% 

less in the water-restricted group than in the 

control animals. The water-restricted animals lost 

21.1% of body mass in 23 days and these animals, 

when allowed water ad libitum, were able to 

recover 71.5% of the lost body mass within 3 

days. 

Borut, A. R. Dmi’el, and A. Shkolnik. 1979. Heat 

balance of resting and walking goats: comparison of 

climatic chamber and exposure in the desert. 

Physiological Zoology 52:105-113. 

This study compared heat-balance experiments 

carried out under standardized conditions in a 

climate chamber with those performed under 

natural conditions, using identical methodology 

and instrumentation. Heat production and 

partitioning of evaporative cooling were measured 

in the black Bedouin goat from the Sinai desert 

when the goats rested or walked on a treadmill in 

a climate chamber (26 oC and 40 oC, relative 

humidity 30%). These were measured in the same 

goats while they were fully exposed to desert 

conditions. Heat production of resting goats was 2 

kcal/kg/hr at 26 oC and morning experiments in 

the field and 2.5 kcal kg-1 hr-1 at 40 oC and noon 

experiments. Heat production of goats walking at 
24 

a speed of 2.60 – 2.95 km hr-1 was 4.1 – 4.9 kcal 

kg-1 hr-1 in both climatic chamber and field 

experiments. Under mild conditions, 26 oC and 

morning, evaporation dissipated up to 50% of heat 

produced. At 40 oC in climatic chamber, 

evaporation equaled heat production, but at noon 

in the desert it increased two-fold. Under these 

desert conditions both resting and walking goats 

had the same excess, 1.72 kcal-1 kg-1 hr, of 

evaporative heat loss over heat production. This 

represents the net heat load imposed by the desert 

environment; its magnitude approximately equals 

the goat’s resting metabolism. In the climatic 

chamber the goats used mostly panting to 

dissipate heat. In the desert, however, the amounts 

of heat dissipated by sweating were twice as great 

as those lost through the respiratory system. These 

high rates of sweating (up to 143 g water-1 m2 –1 hr1

) are attributed to the absorption of solar 

radiation, a factor that does not exist in the 

laboratory but is very prominent in the desert 

environment. 

Brosh, A., B. Sneh, and A. Shkolnik. 1983. Effect of 

severe dehydration and rapid rehydration on the activity 

of the rumen microbial population of black Bedouin 

goats. Journal of Agricultural Science 100:413-421. 

Drinking regimes of Bedouin goats affect their 

feeding behavior and the ruminal environmental 

conditions, as expressed by changes in osmotic 

pressure as well as in pH of the rumen content. 

The osmotic concentration of the rumen content 

of a goat drinking once daily was 330 mOsm kg-1

just before drinking. After water deprivation for 4 

days, the osmotic concentration reached 360 

mOsm-1 kg and, immediately after excessive 

drinking decreased to 82 mOsm-1 kg. After a short 

time, the osmotic concentration increased to 300 

mOsm kg-1 and after 13 hr reached a peak of 440 

mOsm kg-1, mainly owing to the release of 

degradation products. The pH was also affected 

by food consumption. Just prior to drinking, the 

pH in the rumen of dehydrated goats was 6.9. It 

decreased to 6.0 after excessive drinking and 

feeding. Later it ranged between 6.4 and 7.1. Most 

of the microorganisms in the rumen are attached 

to the fiber fraction. No difference could be 

observed in direct bacterial counts in the fluid 

fraction between dehydrated and goats watered 

daily. However, the number of protozoa was 

reduced in dehydrated goats, especially after 

excessive drinking, as some species of protozoa 

seem to explode in a hyposmotic ambient. The 

fermentation capacity of the fiber fraction was 

higher than that of the fluid fraction, indicating 

also the presence of more microorganisms in the 

fiber. In addition, the osmotic changes occurring 

during the dehydration-rehydration cycles had no 

significant effect on fermentation capability of the 

rumen microorganisms. At a low osmotic 

concentration in a NaCl deficient ambient, there 

was some decrease in fermentation rate, but this 

could be nullified with the addition of NaCl, 

which is required for microbial activity. The 

decrease in fermentation rate is not due to its 

effect on the osmotic concentration. The 

microorganisms in the fiber fraction were found to 

be less affected by NaCl deficiency in the ambient 

medium. 

Brosh, A., I. Choshniak, A. Tadmor, and A. Shkolnik. 

1986. Infrequent drinking, digestive efficiency and 

particle size of digesta in black Bedouin goats. Journal 

of Agricultural Science 106:575-579. 

When given access to water once every 4 days, 

black Bedouin goats that were fed dry Lucerne 

hay required, on average, only half the water and 

60% of the gross energy they consumed when 

water was offered to them once daily. 

Digestibility of the feed in these goats increased 

by 4%. The outflow of fluid from the rumen 

slowed down during the water deprivation period. 

A flow rate of 1,080 ml kg-0.75 day-1 was recorded 

during the 1st day of the period and only 350 ml 

kg-0.75 day-1 during the last day. While being 

offered water once daily the outflow from the 

rumen amounted to 1,243 ml kg-0.75 day-1. 

Following the subjection of black Bedouin goats 

to infrequent drinking the mean retention time of 

the digesta in the rumen was extended by 33% 

and in the entire gastrointestinal tract by 43%. It is 

suggested that the slowing down of the ruminal 

flow that followed the subjection of the goats to 

infrequent drinking enabled the particulate matter 

to stay longer in the digestive tract despite their 

smaller size. 
25 

Bullard, R. W., D. B. Dill, and M. K. Yousef. 1970. 

Response of the burro to desert heat stress. Journal of 

Applied Physiology 29:159-167. 

Two female burros were studied with regard to 

regulation of sweating and responses to 

dehydration and rehydration under the natural 

desert conditions of Boulder City, Nevada, in 

July. Sweat in the donkey appeared to be expelled 

in cycles of ≤2 min-1 that occur synchronously all 

over the body surface. The sweating rate was 

determined by both central and skin temperatures. 

Cooling the major portion of the skin area during 

sweating appeared to reduce the magnitude of 

cycles, but not the overall sweating rate until 

general body cooling had occurred. However, heat 

applied locally to the skin or sweat glands had a 

marked stimulating effect suggesting that the local 

temperature of the gland is important in its 

function and that reflex regulation of sweating, 

acting by way of peripheral thermal detectors, is 

less important. The most potent stimulating agent 

upon intradermal injection was epinephrine. Other 

autonomic agents were almost completely 

ineffective upon the rate of sweating. Moderate 

dehydration, amounting to 14% and 9% of body 

mass during desert exposures, did not greatly alter 

blood concentrations, performance, or temperature 

regulation. Rehydration was rapid and precise 

after this degree of dehydration. 

Burke, M. G. 1988. Water economy of tropical feral 

goats. American Zoologist 28:181A. 

The behavioral ecology and population dynamics 

of the feral goats of Aldabra Atoll, Seychelles, 

were studied for 20 months between 1976 and 

1986. The semi arid climate and the availability of 

water influenced the behavior and the timing and 

rate of reproduction of the goats. The only source 

of fresh drinking was rain puddles, which the 

goats used readily. By the end of the six-month 

dry season, however, most such puddles had 

disappeared, and goats drank seawater from tidal 

pools and the lagoon. The goat’s kidneys showed 

normal gross morphology; relative renal 

medullary thickness was within the range reported 

for other feral and domestic goats. The Aldabra 

goats conserved water by producing relatively dry 

feces with mean water content of only 36%, by 

remaining relatively inactive during the hottest 

part of the day, and by feeding primarily at dusk 

and dawn when air temperatures were cooler and 

forage had higher water content and occasional 

dew. Births occurred year round, but a distinct 

peak occurred at the beginning of the dry season. 

Reproductive rates were lower during dry years. 

Cameron, R. D., III. 1972. Water metabolism by 

reindeer (Rangifer tarandus). Ph.D. dissertation, 

University of Alaska, Fairbanks, Alaska, USA. 109p. 

The effects of climatic and nutritional variation on 

body fluid compartmentalization and turnover 

were investigated in female reindeer (Rangifer 

tarandus) using titrated water and sodium sulfate -

35S. An initial field study characterized these 

changes on a seasonal basis under natural grazing 

conditions. Between early winter and late spring 

body mass was either maintained or reduced, 

while total body water (percentage of body mass) 

increased, indicating losses of body solids. Water 

flux rates were higher in the late spring than 

during other seasons; lowest values were recorded 

in early winter. A laboratory study was 

subsequently undertaken to ascertain the 

differential influences of temperature and 

nutrition on water flux. At low temperatures (-5 to 

-20 oC) water flux was linearly related to nitrogen 

intake, and a direct relationship was found 

between the excretion rates of fecal water and 

nitrogen. At higher temperatures (+10 oC) water 

flux increased relative to the intake of nitrogen 

due to higher rates of insensible water loss and an 

increase in the ratio of fecal water to fecal 

nitrogen excretion. Urine volume varies directly 

with water flux, independent of temperature and 

nitrogen intake. Variations in the nutritional status 

and changes in water turnover are discussed in 

relation to climate and the quality and availability 

of feed, and with regard to mechanisms for the 

conservation of energy and nitrogen. 

Cameron, R. D. III and J. R. Luick. 1972. Seasonal 

changes in total body water, extracellular fluid, and 

blood volume in grazing reindeer (Rangifer tarandus). 

Canadian Journal of Zoology 50: 107-116. 
26 

Seasonal changes in total body water, 

extracellular fluid, and blood volume in grazing 

reindeer (Rangifer tarandus) was studied in 1968 

- 1969 at the University of Alaska, Reindeer 

Research Station near Cantwell, Alaska. The 

effects of climatic and nutritional changes on 

body fluid compartmentalization and turnover 

were investigated in grazing female reindeer. 

Total body water volume and turnover, 

extracellular fluid volume, and blood volume 

were estimated using titrated water, sodium 

sulfate -35S, and sodium chromate -51Cr, 

respectively. During winter and spring, body mass 

was either maintained or reduced while total body 

water (percentage of body mass) increased, 

resulting in appreciable losses of total body solids. 

In summer, large gains in body mass were 

accompanied by reduced total body water 

volumes resulting in substantial increases in body 

solids. An apparent fluid shift from the 

intravascular to the extracellular compartment 

during late spring suggested the occurrence of a 

starvation edema. Mean water flux rates (ml day-1 

kg-1 body mass) were higher in late spring than 

during other seasons; lowest values were recorded 

in early winter. Seasonal variations in nutritional 

status as reflected by body composition and fluid 

compartmentalization, and changes in water 

turnover are discussed in relation to climate and 

the quality and availability of forage. The 

complicating influences of pregnancy and 

lactation are also considered. 

Cameron, R. D., J. R. Luick, and R. G. White. 1982. 

Water turnover in reindeer. Pages 189-194 in Use of 

titrated water in studies of production and adaptations 

in ruminants. International Atomic Energy Agency, 

Vienna, Austria. 

The nutritional and climatic effects on water 

turnover in reindeer are described. At low ambient 

temperatures (ca. -20 oC) water turnover is related 

to protein and mineral intake, which is reflected in 

the relations of fecal and urinary water to nitrogen 

and ash excretion via these avenues. As ambient 

temperature increases, respiratory water, fecal 

water, and urine flow increase, resulting in an 

increase in water turnover. 

Cameron, R. D. III, R. G. White, and J. R. Luick. 1976. 

Accuracy of the tritium water dilution method for 

determining water flux in reindeer (Rangifer tarandus). 

Canadian Journal of Zoology 54:857-862. 

The accuracy of the tritium water dilution method 

in estimating water flux was evaluated in reindeer 

(Rangifer tarandus) under various conditions of 

temperature and diet. Two non-pregnant female 

reindeer were restrained in metabolism stalls, 

within controlled-environment chambers, at 

temperatures of +10, -5, and –20 oC; varying 

amounts of a commercial pelleted ration (crude 

protein, 13%) or mixed lichens (crude protein, 

3%) were offered, and water was provided ad 

libitum either as snow or in liquid form. Total 

body water volume, and water turnover rate were 

estimated using titrated water, and the daily 

outputs of and urine were measured for each of 12 

different combinations of diet and temperature. 

Statistical analysis of the data showed that the 

tritium water dilution technique gives accurate 

determinations of total body water flux over a 

wide range of environmental and nutritional 

conditions. 

Carlisle, D. B. and L. I. Ghobrial. 1968. Food and water 

requirements of the dorcas gazelle in the Sudan. 

Mammalia 32:570-576. 

Food and water requirements of the dorcas gazelle 

were studied using field observations in the 

Sudan. The dorcas gazelle (Gazella dorcas) in the 

Sudan does not eat grass during the dry season but 

eat the leaves of Acacia tortilis to the complete or 

almost complete exclusion of other foods. Acacia 

tortilis retains its leaves throughout the year and 

in regions where rain has fallen during the last 

year the moisture content of the leaves is about 

60%. Comparison of the water and caloric 

requirements of penned animals with analyses of 

Acacia leaves should be adequate to provide all 

the food and water requirements of the gazelle 

throughout the dry season without there being a 

need for the animals to drink. 

Carlson, G. P., G. E. Rumbaugh, and D. Harrold. 1979. 

Physiologic alterations in the horse produced by food 

and water deprivation during periods of high
27 

environmental temperatures. American Journal of 

Veterinary Research 40:982-985. 

Eight normal horses were held without access to 

food or water for 72 hr during a period of high 

environmental temperatures. During this period, 

the horses had an average weight loss of 51.6 kg 

(10.7% of body mass). Highly significant 

decreases in extracellular fluid volume (18.6 L) 

and plasma volume (5 L) were observed during 

this period as compared with baseline values. 

Plasma protein, sodium, chloride, and osmolality 

progressively increased in response to 

dehydration, whereas packed cell volume, plasma 

potassium, calcium, magnesium, and phosphate 

were not significantly altered. The dehydration 

and clinicopathologic alterations produced were 

similar to those observed in other species in which 

the principle problem was a water deficit. After 

the end of the experimental dehydration period, 

the horses replaced 62% of the weight loss during 

a 1-hour period with access to water only. 

Choshniak, I. and A. Shkolnik. 1977. Rapid rehydration 

in the black Bedouin goats: red blood cell fragility and 

role of the rumen. Comparative Biochemistry and 

Physiology 56A:581-583. 

The fragility of red blood cells and the role of the 

rumen during rapid rehydration in the Bedouin 

goat were studied. Following dehydration, goats 

regularly drink volumes of water amounting to 30 

– 40% of their body mass. In vitro experiments 

showed that 50% hemolysis of the red blood cells 

of these goats occurred at a concentration of 110 

mM NaCl. Blood plasma concentration dropped 

from 336.5 ± 6.9 mOsm kg-1 before drinking to 

only 303.7 ± 7.6, mOsm kg-1, 6 hr afterwards. 

Changes in plasma volume were moderate. The 

rumen was shown to first retain the water 

imbibed, and to release in only gradually later on: 

within 5 hr following the drinking 18% of the 

ruminal fluid left in the rumen. 

Choshniak, I., A. Brosh, and A. Shkolnik. 1988. 

Productivity of Bedouin goats: coping with shortages of 

water and adequate food. Pages 47-64 in Isotope aided 

studies on livestock productivity in Mediterranean and 

North African countries. International Atomic Energy 

Agency, Vienna, Austria. 

The study was carried out under outdoor summer 

conditions on goats that were watered only once 

every 4 days and goats that were watered once 

daily. Under each of the watering regimes the 

goats were fed alfalfa hay (a high quality 

roughage), and Rhodes grass, and wheat straw, 

medium and low quality feed, respectively. In all 

trials except 1, the goats maintained constant body 

mass. The exception occurred when the goats 

were watered daily while on a diet of wheat straw. 

Infrequent drinking considerably hampered feed 

intake when the goats were fed high quality 

roughage. When wheat straw was fed the intake 

was low but was not affected by drinking. When 

goats were watered infrequently they gulped down 

volumes of water that often caused the osmolarity 

of the rumen fluid to drop from 360 mOsm kg-1 to 

80 mOsm kg-1. Over the entire range of osmotic 

concentration the bacterial populations in the 

goat’s rumen maintained their viability. By 

reducing the fluid flow through the gut, infrequent 

drinking helped to extend the time the digesta 

were retained along the digestive tract. As a result, 

digestibility of the roughage was improved. 

Infrequent drinking was also found to reduce the 

animal’s demand for metabolizable energy. It also 

improved the balance in the utilization of dietary 

protein while not interfering with the ability to 

recycle urea. Frequent watering of ruminants in 

the desert is likely to increase their demand for 

food, lower their gain in digestible energy, and 

increase their demand for digestible energy and 

make it more difficult for them to balance their 

energy budget. Improving feed quality for animals 

in the desert, when water availability declines, is 

also not advantageous. It may only increase the 

animal’s needs for water, render them dependent 

on frequent drinking, and restrict their grazing 

area to the close vicinity of water sources. 

Choshniak, I, C. Wittenberg, and D. Saham. 1987. 

Rehydrating Bedouin goats with saline: rumen and 

kidney function. Physiological Zoology 60:373-378. 

Following a period of water deprivation, Bedouin 

goats became rehydrated by drinking 0.9% NaCl 

solution. During one continuous drinking bout, 
28 

these goats ingested 3.26 ± 0.42 liters of saline 

and regained their initial body mass. The outflow 

from the rumen during the first hour after drinking 

saline amounted to 596 ± ml hr-1, eight times the 

rate recorded during the time when goats became 

rehydrated when drinking water. Within an hour 

after they had drunk saline, urine flow exceeded 

the predrinking levels. Six hours following 

drinking it barely regained the rate recorded at the 

end of the dehydration period. The pattern of 

changes in the glomerular filtration rate and renal 

plasma flow was similar to that observed with 

urine flow. It is concluded that the rumen in the 

Bedouin goat “stores” water following rapid 

rehydration with water but does not function as an 

osmotic protective mechanism with the animals 

become rehydrated with saline. Presumably, the 

rate at which water leaves the rumen is inversely 

related to the hypotonicity of the rumen fluid. 

Choshniak, I, C. Wittenberg, J. Rosenfeld, and A. 

Shkolnik. 1984. Rapid rehydration and kidney function 

in the black Bedouin goat. Physiological Zoology 

57;573-579. 

Black goats, tended by Bedouin tribesmen in the 

extreme deserts of the Middle East, drink only 

once every 2 – 4 days and imbibe amounts of 

water that often exceed 40% of their dehydrated 

body mass. The water that the goats drink 

copiously is first retained in the rumen and only 

gradually flows into the other body fluid 

compartments. Five hours after the drinking, 81% 

of the water imbibed was still stored in the 

spacious rumen of the goat. The kidney of the 

Bedouin goat responded to the voluminous 

drinking by a drop in the blood flow that was 

followed by a compatible drop in both the 

glomerular filtration rate and urine flow. The 

urine flow, even 4 hr following drinking, was 

below the rate recorded in the dehydrated animal. 

Urine Na+

 concentration that amounted to 80.3 

mM in the dehydrated animal dropped to only 

37.7 mM following the drinking. A drop (from 

144 mM to 49 mM) was also simultaneously 

recorded in Cl-

 concentration; K+ and urea 

concentration, however, changed only slightly. It 

is suggested that the rumen in the goat serves as a 

water reservoir that helps maintain the osmotic 

stability of the body proper. The kidneys in these 

animals efficiently conserve the water imbibed as 

well as the body’s Na+ and Cl-

. Studies of sheep 

that assign similar roles to the rumen and kidneys 

indicate that the physiological mechanism 

described in the present study is generally shared 

by ruminants tended in a pastoral system. 

Cloete, G. and O. B. Kok. 1986. Aspects of the water 

economy of steenbok (Raphicerus campestris) in the 

Namib Desert. Madoqua 14:375-387. 

Behavioral and physiological aspects of the water 

economy of steenbok (Raphicerus campestris) in 

the Namib Desert were investigated. Field 

observations indicate that the antelope are 

normally independent of free water, their main 

water source being dietary. Daily dietary water 

intake of captive steenbok was determined as 

342.5 ml, while water turnover rate was calculated 

as 135 ml day-1. Urine analyses and kidney 

morphology do not suggest particular adaptations 

of renal function for desert conditions, while 

thermoregulatory behavior appears to play a major 

role as a water-conserving mechanism. 

Coppock, D. L., J. E. Ellis, and D. M. Swift. 1988. 

Seasonal patterns of activity, travel and water intake for 

livestock in South Turkana, Kenya 14:319-331. 

The nomads of Ngisonyoka Turkana exploit a 

harsh and seasonally variable environment using 5 

livestock species in a dynamic management 

system. Season, species, and management 

influenced animal activity budgets during one 

annual cycle in 1981 - 1982. Relative to the long 

dry season, the brief wet season was a time of 

high resource abundance, increased water intake 

(cattle, goats, sheep), reduced travel (all species) 

and increased time available for feeding (cattle, 

goats, sheep, donkeys). Browsing camels 

generally showed the least seasonal change in 

activity budgets and water intake, while grassdependent cattle exhibited the most change. 

Degen, A. A. 1977a. Fat-tailed Awassi and German 

Mutton Merino sheep under semi-arid conditions I: Total 

body water, its distribution and water turnover. Journal 

of Agricultural Science 88:693-698. 
29 

The total body water, its distribution and water 

turnover were measured in native fat-tailed 

Awassi sheep and German Mutton Merino sheep 

under semi-arid conditions using titrated water. 

Total body water, extracellular fluid volume and 

plasma volume were measured during summer 

while sheep were grazed in natural pasture that 

remained as dried stem-cured hay and in the 

winter while they grazed lush natural pasture. No 

differences were found between breeds in any of 

the measurements in both seasons. Within both 

breeds, the percentage of titrated water space and 

extracellular fluid volume were larger in the 

summer whereas the percentage of plasma volume 

remained the same. Total body water and water 

turnover were measured in these breeds in 8 trials 

while the sheep grazed in native pasture in the 

autumn, winter, and spring, shrubs in the winter 

and legumes in the summer. Water and shade 

were freely and easily accessible throughout the 

grazing period. The total body water was found to 

be consistently lower in the Awassi, indicating a 

higher energy reserve. The water turnover in 24 hr 

kg-1 wt0.82 was found to be higher in the German 

Mutton Merino in all trials; the differences ranged 

between 3 and 28%. However, in only 2 of 8 trials 

were the differences significant. Thus, water 

turnover was only slightly lower in the Awassi 

although this breed evolved under Middle Eastern 

arid and semi-arid regions. 

Degen, A. A. 1977b. Fat-tailed Awassi and German 

Mutton Merino sheep under semi-arid conditions II: 

Total body water and water turnover during pregnancy 

and lactation. Journal of Agricultural Science 88:699-

704. 

The total body water and water turnover of fattailed Awassi females, a desert adapted breed, and 

German Mutton Merino females, a temperate 

environment breed, were measured during the 3rd, 

4th, and 5th month of pregnancy and during the 

first month of lactation using titrated water. 

Measurements were taken under grazing 

conditions with unrestricted water in a semi-arid 

region. Both breeds of sheep lost weight during 

this period. The percentage of total body water 

increased, especially during the 5th month of 

pregnancy when the German Mutton Merino 

increased their total body water by 5.2% and the 

Awassi by 1.0%. It was concluded that the 

nutritive intake was not sufficient to supply the 

increased energy demands and that sheep were 

mobilizing body solids, the German Mutton 

Merino at a faster rate. The German Mutton 

Merino females turned over about 20% more 

water per kg wt0.82 during pregnancy and lactation 

than did the Awassi ewes. There was little 

difference in water turnover between the control 

and pregnant sheep within their breed during 

gestation. During lactation the experimental 

Awassi increased their water turnover by 29% 

over the control Awassi and the experimental 

German Mutton Merino increased their water 

turnover by 26% over the control German Mutton 

Merino. In both breeds the increase in water 

turnover during lactation was smaller than that 

found in other lactating semi-arid ruminants and 

the increase in water turnover during pregnancy 

and lactation was smaller than that recommended 

by the Agricultural Research Council. 

Degen, A. A. 1977c. Fat-tailed Awassi and German 

Mutton Merino sheep under semi-arid conditions III: 

body temperature and panting rate. Journal of 

Agricultural Science 89:399-405. 

Rectal, external auditory meatus, and skin 

temperatures and panting rates were measured in 

native fat-tailed Awassi and imported German 

Mutton Merino sheep. The Awassi evolved under 

desert conditions, have a localized fat deposit, 

course carpet wool, long ears, and long spiral 

horns (males). In contrast, the German Mutton 

Merino evolved under temperate conditions, have 

well-distributed fat, medium fine wool, short 

straight ears and are polled. The study was carried 

out during the summer in the northern part of the 

Negev desert. The mean daily rectal temperature 

fluctuation was higher in the German Mutton 

Merino than in the Awassi (1.78 oC vs. 1.08 oC). 

The external auditory meatus temperature was 

lower than the rectal temperature by 1.5 oC in the 

German Mutton Merino and by 1.7 oC in the 

Awassi, indicating a cooler brain temperature. The 

maximum skin temperature was similar to the 

maximum rectal temperature in both breeds, thus 

sweating was of little importance. The panting 

rate of the German Mutton Merino increased fivefold (40.6 – 199.4 pants min-1) whilst the rate of 
30 

the Awassi increased four-fold (35.3 – 135.0 pants 

min-1). There was no between breed difference in 

either the rectal temperature or panting rate until 

25 - 30 oC ambient temperature and it is thought 

that the higher rectal temperature of the German 

Mutton Merino at this ambient temperature might 

have triggered the higher panting rate. It seems 

that the German Mutton Merino use panting to a 

greater extent than the Awassi, whereas the 

Awassi dissipate heat through the skin more 

efficiently than the German Mutton Merino. It is 

concluded that both breeds are thermostable, 

much of the between breed difference in rectal 

temperature can be attributed to their anatomical 

differences. 

Degen, A. A. and B. A. Young. 1981. Effect of air 

temperature and feed intake on live weight and water 

balance in sheep. Journal of Agricultural Science 

96:493-496. 

Environmental conditions and total feed intake 

influence the water intake of sheep. In general, 

high temperatures increase the requirements for 

water needed for evaporative cooling and high 

feed intakes necessitate more water for excretion 

of waste products. This study was designed to 

measure the partition of water output in sheep 

maintained at 4 air temperatures and offered 4 

levels of a ration. 

Degen, A. A. and M. Kam. 1991. Energy intake, 

nitrogen balance and water influx of Dorper sheep 

when consuming different diets. Journal of Arid 

Environments 21:363-369. 

Dorper sheep are well adapted to arid areas and 

inhabit extreme deserts. We hypothesized that 

these sheep would have low energy and nitrogen 

requirements, allowing them to be raised in these 

areas. We measured energy intake, N requirement 

and water influx of Dorpers (40 kg body mass) 

that were offered either Lucerne hay (17.5% crude 

protein), Lucerne hay plus wheat straw or wheat 

straw (3.25% crude protein) and water ad libitum. 

Dry matter digestibility and apparent digestible 

energy as a percent of gross energy were 67.7% 

and 66.1%, respectively, for Lucerne hay, and 

46.5% and 50.7%, respectively, for wheat straw. 

Dorpers gained body mass and were in positive N 

balance on Lucerne hay plus wheat straw and lost 

body mass and were in negative N balance on 

wheat straw. Metabolizable energy intake was 925 

kJ kg-.075/day on Lucerne hay, 706 kJ kg-0.75 day-1

on Lucerne hay plus straw, and 420 kJ kg-0.75.day-1

on wheat straw. Apparent N digestibility of 

Dorper was 76.9%, and 68.1% and 24.3% for 

Lucerne hay, Lucerne hay plus wheat straw and 

wheat straw respectively, and their water influxes 

on these respective diets were 3.74 L day-1, 3.17 L 

day-1, and 1.68 L day-1. Energy and N 

requirements of Dorpers were similar to many 

sheep breeds and greater than a number of desert 

sheep and desert herbivores. We concluded that 

Dorpers did not appear to have special 

physiological adaptations of low energy and 

nitrogen requirements. 

Dill, D. B., M. K. Yousef, C. R. Cox, and R. G. Barton. 

1980. Hunger vs. thirst in the burro (Equus asinus). 

Physiology and Behavior 24:975-978. 

The burro can withstand deprivation of food and 

water for up to 48 hr even in summer heat. The 

relationships of hunger and thirst following 

periods of deprivation were studied. In 8 periods 

of deprivation maximum temperatures ranged 

from 35 to 45 oC and estimated increase in 

osmotic pressure in 2 burros ranged up to 17%. 

Given free choice of hay and water at the end of 

deprivation they chose hay always when estimated 

increase in osmotic pressure was less than 10%. In 

1 case the second 24-hour period included an 8-

hour walk. In this case the estimated increase in 

osmotic pressure was 17% in both and both chose 

water first. Their ability to eat dry hay after long 

periods of dehydration is essential to their survival 

in hot deserts where they can graze for day before 

returning to a water source. 

Dmi’el, R. and D. Robertshaw. 1983. The control of 

panting and sweating in the black Bedouin goat: a 

comparison of two modes of imposing a heat load. 

Physiological Zoology 56:404-411. 

The black Bedouin goat uses both panting and 

sweating as modes of evaporative heat loss. The 

control of panting and cooling was studied by 
31 

examining the body temperature distribution 

under heat loads which produced equivalent levels 

of evaporative heat loss, namely, solar radiation 

and high air temperature conditions, conducted in 

indoor and outdoor settings, respectively. Heat 

exposure induced by high air temperature resulted 

in a proportionally greater respiratory water loss 

than did outdoor exposure to solar radiation; the 

greater respiratory cooling was related to higher 

hypothalamic and arterial temperatures but lower 

skin temperatures. However, solar radiation 

resulted in a higher temperature of the skin under 

irradiated fur, and this was associated with a 

greater cutaneous moisture loss. Thus, the mode 

of evaporation was concluded to be appropriate to 

the thermal stimulus: higher nasal temperature 

resulted in a predominant panting response, and 

high skin temperature invoked greater sweating. 

The gradient between arterial and hypothalamic 

temperature was not necessarily correlated with 

panting, providing evidence that blood flow 

through the countercurrent heat exchanger, the 

carotid rete mirabile, was utilized only when 

hypothalamic temperature rose above a critical 

level. 

Dmi'el, R. 1986. Selective sweat secretion and panting 

modulation in dehydrated goats. Journal of Thermal 

Biology 11:157-159. 

Sweating from the trunk and the head, respiratory 

water loss, oxygen consumption and rectal 

temperature, were measured in daily watered and 

in dehydrated black Bedouin goats exposed to 

summer conditions in the desert. After 72h of 

water deprivation the goats lost 19.5% of their 

body mass. Although rectal temperatures and total 

evaporation were similar in both states of 

hydration, a 3-fold reduction in the sweating from 

the trunk, associated with a 26% decrease in 

metabolic rate, was found in the dehydrated goats. 

Concurrently, the rates of sweating from the head 

and the respiratory water loss were increased 2.9 

and 2.3-fold, respectively. It is proposed that the 

selective sweat secretion and panting modulation 

enable a preferential brain cooling in the 

dehydrated goat. 

El Hadi, H. M. and Y. M. Hassan. 1982. Seasonal 

changes in water metabolism of Sudan Desert sheep 

and goats. Pages 133-142 in Use of titrated water in 

studies of production and adaptations in ruminants. 

International Atomic Energy Agency, Vienna, Austria. 

Seasonal changes that occur in body mass, body 

temperature, total body water, and water turnover 

were investigated in grazing sheep and goats 

using titrated water at different times of year to 

understand how different breeds adapt to the 

environmental conditions in Sudan. Sheep had 

lower body water content and turnover rates than 

goats. Goats maintained a lower body temperature 

under hot conditions than the sheep, possibly 

because of a lower food intake and maintenance 

requirement and a higher evaporative heat loss. It 

might be deduced from this that goats will survive 

better when food is in short supply provided 

sufficient water is available, and that sheep will 

grow relatively better when food is adequate. 

However, in the absence of comparative 

information on reproductive performance under 

these conditions it is not possible to make an 

unequivocal statement about the relative 

productivity of these types of small ruminants. 

Etzion, Z., N. Meyerstein, and R. Yagil. 1984. Titrated 

water metabolism during dehydration and rehydration in 

the camel. Journal of Applied Physiology 56:217-220. 

The metabolism of titrated water in the camel was 

compared in 2 10-day periods, 1 when water was 

readily available and the second during 

dehydration. There was a radically depressed 

metabolism after 2 days of dehydration. Two 

other experiments examined the absorption rate of 

drinking water. In 1 experiment drinking water 

was labeled with tritium, and in the second 

experiment dilution of tritium-labeled blood was 

examined. In both experiments there was a rapid 

uptake and dilution of the blood, which continued 

up to day after drinking. The results are in accord 

with other data showing changes in erythrocyte 

shape 4 hr after rapid rehydration. It is concluded 

that there is a rapid absorption of water in the 

dehydrating camel. 
32 

Etzion, Z. and R. Yagil. 1986. Renal function in camels 

(Camelus dromedaries) following rapid rehydration. 

Physiological Zoology 59:558-562. 

The desert camel, like the goat, rapidly replaces 

lost water after being severely dehydrated. In 

contrast to the goat, however, the camel quickly 

absorbs water into its bloodstream, which allows 

for a rapid return to normal of its renal function. 

The glomerular filtration rate, renal plasma flow, 

and urine flow return to normal within 30 minutes 

of drinking. The urine becomes highly diluted in 

appearance as well. The changes in urea 

metabolism are probably associated with the 

decline in antidiuretic hormone concentrations. To 

prevent serious hemodilution, aldosterone 

secretion accounts for the slight drop in 

glomerular filtration rate and renal plasma flow 2 

hr following drinking. The camel has thus adapted 

to the desert not only by being able to withstand 

severe dehydration but also by being able to 

rapidly restore body functions, especially renal 

function. 

Farid, M. F. A. 1985. Long-term adaptation of sheep to 

low protein intake under simulated drought conditions. 

Journal of Arid Environments 8:79-83. 

Barki sheep maintained on low protein diets or fed 

decreasing amounts of protein, were able to adapt 

by reducing urinary nitrogen excretion, and 

subsequent recycling of conserved nitrogen to the 

rumen, as reflected upon the more efficient 

utilization of the apparently digested nitrogen. 

After 50 - 60 days on the low protein diets, sheep 

activated positive nitrogen balance while 

receiving only 60% of their maintenance 

requirements. Similarly, gradually decreasing the 

level of protein intake enabled sheep to adapt and 

improve their state of nitrogen balance. The 

findings are discussed in the light of their value 

for the supplementary feeding and management of 

sheep on arid and semi-arid rangelands. 

Farid, M. F. A., H. M. Abou-El Nasr, N. I. Hassan and F. 

Z. Swidan. 1989. Long-term adaptation of sheep to low 

protein roughage diets: effects of water deprivation and 

urea supplementation in the drinking water. Journal of 

Arid Environments 16:211-216. 

Nine Barki x Merino crossbred rams were fed low 

protein roughage diets in 3 groups: daily watering, 

and intermittent watering every 3 days with and 

without urea supplements in the drinking water. 

The experiment lasted 63 days to investigate 

possible long-term adaptive responses. Live body 

masses was recorded every 2 weeks, and urine 

was collected for 3 consecutive days every 2 

weeks. The experiment ended with a 10-day 

rehydration period. Daily dry matter intake was 

not affected by water deprivation or urea 

supplementation, and the amounts offered were 

apparently insufficient for maintenance in all 

groups. Nitrogen intake was significantly greater 

in the urea-supplemented group. All groups 

showed a loss of nitrogen in urine at the beginning 

of the experiment, 136 to 157% of total nitrogen 

intake. However rapid adaptation was observed 

and after 1 month urinary nitrogen excretion 

represented 57 to 75% of intake. The ureasupplemented group constantly excreted more 

nitrogen, but the trend of adaptation was similar in 

all 3 groups. All sheep lost weight that amounted 

to 2.1, 2.1, and 4.1% of their initial weight in the 

control and water-deprived with and without urea 

supplementation, respectively. On rehydration, the 

latter 2 groups restored or slightly exceeded their 

initial weight. 

Finberg, J. P. M., R. Yagil, and G. M. Berlyne. 1978. 

Response of the rennin-aldosterone system in the 

camel to acute dehydration. Journal of Applied 

Physiology 44:926-930. 

Plasma rennin activity, rennin substrate 

concentration, aldosterone concentration, and 

Cortisol levels were determined in 5 camels 

during dehydration (8 – 10 days of complete 

denial of water) and at timed intervals after rapid 

rehydration in cool spring and hot summer 

weather. Plasma sodium concentration increased 

from 138 ± 3.7 to 147 ± 2.5 (mean ± SE) meq L-1

during spring dehydration, and from 146 ±1.3 to 

1.14 ± meq L-1 during dehydration in the summer. 

Plasma sodium concentration returned to control 

levels over the course of several hours following 

rapid rehydration. Only minor changes in plasma 

potassium concentration occurred. The hormonal 

changes were accentuated in the summer 

dehydration. Plasma rennin activity increased on 
33 

dehydration, and returned to control levels over 

the course of several hours following rehydration. 

Aldosterone concentration increased slightly on 

dehydration but was markedly elevated 24 hr after 

rehydration. Rennin substrate concentration 

showed a slight increase following rehydration in 

the spring. Changes in cortisol were insignificant. 

The results are consistent with the role for 

angiotensin and aldosterone in enhancing sodium 

and water reabsorption from kidney and large 

intestine on dehydration in the camel. 

Finch, V. A. 1972. Thermoregulation and heat balance 

of the East African eland and hartebeest. American 

Journal of Physiology 222:1374-1379. 

Energy exchange between animals and their 

environment was assessed by estimating the total 

energy balance in the field under conditions of 

intense solar radiation in a thermoneutral 

temperature zone. Two representative species 

were chosen: the eland (Taurotragus oryx), which 

uses sweating primarily, and the hartebeest 

(Alcelaphus buselaphus), which uses panting 

primarily as a means of evaporative cooling. 

Results show that evaporative cooling in both 

species varies in relation to changes in skin 

temperature and not to changes in body 

temperature. Estimation of the heat balance 

showed that the eland absorbed 40% and the 

hartebeest 34% of the potential impinging 

radiation. Metabolic heat contributed to 10 - 12% 

to the total heat load. Reradiation from the fur 

surface liberated 69% in the eland and 80% in the 

hartebeest of the absorbed heat. Convection 

contributed 4 - 6% to the total heat dissipation at 

the fur surface. The eland eliminated 78% of the 

remaining absorbed and metabolic heat through 

sweating, 20% through respiratory cooling, and 

stored 2%. The hartebeest eliminated 33% of the 

remaining absorbed and metabolic heat through 

cutaneous evaporation, 61% through panting, and 

stored 6%. Conductance of heat through the fur of 

the hartebeest is 14% of that in the eland. 

Finch, V. A. and J. M. King. 1982. Energy-conserving 

mechanisms as adaptations to under nutrition and 

water deprivation in the African zebu. Pages 167-178 in

Use of titrated water in studies of production and 

adaptations in ruminants. International Atomic Energy 

Agency, Vienna, Austria. 

In a study designed to simulate pastoral cattle 

management practices on marginal and rangelands 

in Kenya, the physiological adaptations for energy 

conservation were investigated in African Zebu 

cattle during a period of under nutrition and water 

deprivation. In experimental design, the food 

available to cattle was restricted to 50% of 

maintenance, watering reduced to every 2 days 

and distances walked increased from 8 to 16 km 

day-1. Restricting food for nearly 3 months 

resulted in a 13 - 14% weight loss in cattle. A 2-

day watering regime did not decrease food intake. 

Cattle that walked longer distances lost slightly 

more weight, but not significantly more. There 

was a significant overall reduction in water 

requirements. Slowing water turnover is seen as 

adaptive in a water-limited environment. Higher 

solar intensities increased water turnover 

somewhat, as did extending walking distances. 

The resting metabolic rate of cattle on restricted 

food and water was reduced 30% below that of 

well-fed and daily watered cattle. This reduction 

in metabolic requirements would result in 

conserving energy in dry seasons. Cattle became 

more thermolabile when offered smaller quantities 

of food. A heat debt was incurred at night and 

sweating rates were regulated at low levels during 

the day, resulting in heat storage. It is suggested 

that this is a mechanism by which energy is 

conserved through increasing thermogenesis to 

maintain body temperature within the normal 

range. 

Gabor, T. M., E. C. Hellgren, and N. J. Silvy. 1997. 

Renal morphology of sympatric suiforms: implications 

for competition. Journal of Mammalogy 78:1089-1095. 

The ability to conserve water in collared peccaries 

(Dicotyles tajacu) and feral hogs were assessed by 

comparing renal morphology in free-ranging 

populations living sympatrically in southern 

Texas in 1994 – 1995. Kidneys of collared 

peccaries had relatively larger and thicker 

medullae and presumably a greater capacity to 

concentrate urine than feral hogs. Renal indices of 

peccaries were similar to values predicted from 

allometric functions, whereas indices of hogs 
34 

were smaller than predicted. Renal mass of hogs, 

when scaled by body mass0.85 was larger than that 

of peccaries. Indices of renal function from this 

study were greater than values reported previously 

for these species. Geographic variation and 

adaptation during growth may play a role in renal 

morphology. Genetic constraints probably control 

large-scale differences, constraining feral hogs to 

being less suited to water-stressed environments. 

Results were consistent with predictions that 

peccaries should have a competitive advantage 

over hogs in xeric environments with minimal 

surface water because of ecophysiology. 

However, a suite of environmental, behavioral, 

and functional factors appears to control 

competitive interactions between native peccaries 

and introduced hogs. 

Ghobrial, L. I. 1970. A comparative study of the 

integument of the camel, dorcas gazelle, and jerboa in 

relation to desert life. Journal of Zoology 160:509-521. 

A comparative histological study of the 

integuments of the dorcas gazelle (Gazella 

dorcas), jerboa (Jaculus jaculus), and the camel 

was conducted. Tubular sweat glands are present 

in the skin of the dorcas gazelle and the camel but 

not in the jerboa. Hairs occur in groups in the skin 

of jerboa and camel but occur singly in the Dorcas 

gazelle where they are of two types; short under 

hairs and long covering hairs. Each hair follicle is 

associated with a sebaceous gland. Both the 

unkeratinized epidermis and its horny layer are 

comparatively thin in the jerboa and gazelle, and 

in dry air this may permit greater loss of water by 

transpiration than in the camel, which has a 

comparatively thick epidermis. 

Ghobrial, L. T. 1970. The water relations of the desert 

antelope Gazella dorcas. Physiological Zoology 43:249-

256. 

Water turnover, routes of water loss, and water 

intake rates were studied in captive dorcas gazelle 

(Gazella dorcas). Daily free-water intake rates 

averaged 3.1% and 4.5% of body weight during 

winter and summer, respectively. Daily intake of 

preformed water averaged 0.2% and 0.15% of 

body mass during winter and summer, 

respectively. Daily urine output in winter 

averaged 2.1% of body mass and had solute 

concentrations of 1.4 osm L-1. In summer, daily 

urine output averaged 1.4% of body mass and had 

solute concentrations of 1.2 osm L-1. Average 

fecal production averaged 0.3% of body mass 

with water content of 52%. During summer, 

average fecal production averaged 0.17% of body 

mass with water content of 51%. Gazelles began 

to sweat at 25 oC. Cutaneous water loss at 20 – 22 

oC was 2.8 – 5.6 g hr-1 m2-1; at 23 – 25 oC, was 

28.2 – 56.4 g hr-1 m2-1; at 26 – 30 oC, was 81.8 – 

87.4 g hr-1 m2-1. Respiratory rate increased from 45 

– 55 breaths min-1 at 28 oC to 50 – 75 breaths min1

 at 29 oC. Respiratory water loss was 0.15 – 0.35 

mg min-1. Total respiratory and cutaneous water 

loss was 6 – 12 g hr-1 at 32 – 35 oC. 

Ghobrial, L. I. 1974. Water relation and requirement of 

the Dorcas gazelle in the Sudan. Mammalia 38:88-107. 

Thirty dorcas gazelle (Gazella dorcas dorcas) 

were studied for: the actual calories and water 

requirements in comparison to the calculated 

amount of moisture which would be gained from 

the preformed water in green acacia leaves, if the 

required calories were to be consumed; the 

tolerance of the gazelle to the absence of free 

water, and its physiological and behavioral 

adaptation for conservation of water and 

thermoregulation. Field studies on the 

distribution, habit, and habitat of the dorcas 

gazelle during the two dry seasons, the hot 

summer, and cold winter were carried out Sudan. 

Ghobrial, L. I. 1976. Observations on the intake of sea 

water by the Dorcas gazelle. Mammalia 40:489-494. 

Artificial sea water with varying salt 

concentrations were provided to dorcas gazelles 

(Gazella dorcas) without access to other water 

sources to determine the effect on food intake, 

urine output, body mass, and chloride 

concentration in urine. Gazelles did not 

voluntarily drink seawater even when deprived of 

fresh water. Water intake and food intake 

increased with decreasing salt concentrations of 

water; urine output increased and urine 

concentration decreased in association with 
35 

decreases in salt concentration. Body mass 

decreased with increasing salt concentration. 

Ghobrial, L. I. and J. L. Cloudsley-Thompson. 1966. 

Effect of deprivation of water on the dorcas gazelle. 

Nature 212:306. 

The dorcas gazelle (Gazella dorcas) requires 

water or succulent food in order to maintain 

homeostasis in desert conditions. It loses weight 

steadily on a diet of dry millet without water. 

Feeding ceases when 14 – 17% of normal body 

mass has been lost and the animals appear weak 

and emaciated. This may take up to 12 days under 

winter conditions at Khartoum when the air 

temperature ranges between 10 and 30 oC with a 

relative humidity varying from 20 to 40%; but, in 

summer, when air temperature fluctuates from 35 

to 45 oC, with relative humidity varying 10 to 

30%, gazelles cannot survive for more than about 

5 days without water. Two experimental animals 

died after 6 days water deprivation, during which 

they lost 24% of their original body mass. This 

contrasts with a loss of 30%, which can be 

tolerated without ill effects by the camel and 

about 12%, which can be withstood by man and 

most other animals. During dehydration, the blood 

urea of gazelles increases from 5 – 10 mg 100 ml-1

to 70 – 110 mg 100 ml-1 (in the animals that died 

it reached 225 mg 100 ml-1). At the same time, the 

hemoglobin content of blood increases from 14 – 

18 g 100 ml-1 to 20 – 29 g 100 ml-1, the hemocrit 

from 40 – 55% to 55 – 59% and the plasma 

protein from 4.5 – 5.5 g 100 ml-1 to 5.5 – 7.0 g 

100 ml-1. These results, accompanied by an 

increase in electrolytes, indicate a decrease in 

extracellular water and a concentration of the 

contents of body fluids, even though urine 

production is reduced from about 200 – 700 ml to 

30 – 80 ml day-1 and the amount of water lost with 

the feces is reduced by 50%. 

Ghosh, P. K., M. S. Khan, and R. K. Abichandani. 1976. 

Effect of short-term water deprivation in summer on 

Marwari sheep. Journal of Agricultural Science 87:221-

223. 

Effect of 24 hr and 48 hr of water deprivation on 

glomerular filtration rate (GFR), and on blood and 

urine electrolyte levels in Marwari sheep of the 

Rajasthan Desert, India have been recorded. Body 

mass, urine volume, GFR, and erythrocyte sodium 

concentration in these animals registered 

considerable decreases due to dehydration. Both 

plasma sodium and urinary potassium 

concentrations remained unaffected. While 

plasma potassium was somewhat reduced, the 

potassium in red blood cells increased after 48 hr 

of water deprivation. The most remarkable 

response was in the concentration of urinary 

sodium, which rose to more than double the 

normal level. 

Giddings, S. R. 1990. Water metabolism in the 

gemsbok (Oryx gazella). MS Thesis. University of 

Pretoria, Pretoria, South Africa. 

Water metabolism in the gemsbok (Oryx gazella) 

was studied in the laboratory using titrated water 

and 51Cr. The distribution of gemsbok is confined 

to the arid regions of Southern Africa, where 

surface water may be limited or saline in nature. 

Failure to obtain adequate water from the diet may 

lead to dehydration and/or imbibition of saline 

water. The goal of this study was to determine 

some of the effects of dehydration and the intake 

of saline water on the physiology of the gemsbok. 

Fewer significant changes in the variables 

measured were found between fresh and saline 

water acclimated animals, than between hydrated 

and dehydrated animals. It was concluded that the 

effects of dehydration were more stressful than 

those resulting from the imbibition of saline 

water. The regulation of plasma fluid volume and 

the intracellular fluid volume, at the expense of 

the interstitial fluid, was found to be an important 

determinant of survival in dehydrated animals. 

Similarly, the regulation of blood variables 

ensured the continued functioning of the 

circulatory system. Dehydration, and to a lesser 

extent, the imbibition of saline water, resulted in a 

non-significant decline in the body water pool. 

Water turnover also declined when saline water 

was imbibed, indicating that water-conserving 

mechanisms were operative. Renal function was 

significantly altered by dehydration, whereas 

imbibition of saline water had less effect. The 

trends recorded indicated that the kidney was 

responsible for the excretion of excess electrolytes 

and the conservation of water. Another important 
36 

water conserving mechanism recorded in 

dehydrated animals involved the increased energy 

assimilation from food eaten. In addition fecal 

water loss was reduced in dehydrated gemsbok 

and to a lesser extent in gemsbok that had imbibed 

saline water. 

Gotaas, G., E. Milne, P. Haggarty, and N. J. C. Tyler. 

2000. Energy expenditure of free-living reindeer 

estimated by the doubly labeled water method. Rangifer 

20:211-219. 

The doubly labeled water (DLW) method was 

used to measure total energy expenditure (TEE) in 

3 male reindeer (Rangifier tarandus) aged 22 

months in winter (February) while the animals 

were living unrestricted at natural mountain 

pasture in northern Norway (69 20'N). The 

concentration of 2

H and 18O were measured in 

water extracted from samples of collected form 

the animals 0.4 and 11.2 days after injection of 

isotopes. Calculated rates of water flux and CO2

production were adjusted to compensate for 

estimated losses of 2

H in fecal solids and in 

methane produced by microbial fermentation of 

forage in the rumen. The mean specific TEE in the 

three animals was 3.057 W kg-1 (range 2.436 - 

3.728 W kg-1). This value is 64% higher than TEE 

measured by the DLW method in four captive, 

non-pregnant adult female reindeer in winter and 

probably mainly reflects higher levels of 

locomotor activity in the free-living animals. 

Previous estimates of TEE in free-living rangifier 

in winter based on factorial models range from 

3.038 W kg-1 in female woodland caribou (R. t. 

caribou) to 1.813 W kg-1 in female Svalbard 

reindeer (R. t. platyrhyncbus). Thus, it seems that 

existing factorial models are unlikely to 

overestimate TEE in reindeer/caribou: they may, 

instead, be unduly conservative. While the present 

study serves as a general validation of the factorial 

approach, we suggest that the route to progress in 

the understanding of field energetics in wild 

ungulates is via application of the DLW method. 

Haggarty, P. and R. E. Haugerud. 1999. Quantifying the 

free-living energy exchanges of Arctic ungulates with 

stable isotopes. Rangifer Report No 4:10. 10th Arctic 

Ungulate Conference, 9-12 August 1999, University of 

Tromso, Tromso, Norway (Abstract). 

When natural diets meet an animal's requirement 

for energy, other essential nutrients will usually be 

supplied in amounts at least sufficient for survival. 

Knowledge of the energy requirements of free 

ranging species under typical conditions is 

important in assessing both their nutritional needs 

and their ecological relationships. The doubly 

labeled water (DLW) method is currently the most 

promising objective field of methodology for 

estimating free-living energy expenditure but 

expenditure is only equal to the energy 

requirement when an animal is in energy balance. 

Reproduction and seasonal cycles of fat 

deposition and utilization represent significant 

components of the energy budget of Artic 

ungulates but the information gained in the course 

of a typical DLW study may be used to estimate 

processes such as milk output and fat storage and 

mobilization in order to predict requirements from 

expenditure. The DLW method has been 

exhaustively validated under highly controlled 

conditions and the introduction of innovations 

such as fecal sampling for the estimation of body 

water isotopic enrichment, the availability of 

appropriate correction factors and stoichiometries 

for known sources of error, and the iterative 

calculation of unknown parameters, have 

produced a methodology suitable for use in 

species under truly free ranging conditions. The 

few studies carried out so far in Arctic ungulates 

indicate that previous predictions have generally 

underestimated the true level of expenditure, that 

there is considerable between animal variation in 

the level of expenditure and that this is largely 

determined by physical activity. The 

disadvantages of the DLW methodology are that it 

remains expensive and the isotope analysis is 

technically demanding. Furthermore, although 

DLW can provide and accurate value for free 

living energy expenditure, it is often important to 

have information on the individual components of 

expenditure, for example the relative contribution 

of physical activity and thermoregulatory 

thermogenesis, in order to interpret the values for 

overall expenditure. For these reasons the most 

valuable use of the DLW method in the field may 

be to validate factorial models and other 

approaches so that they may be used with 

confidence. Additional important information on 

the energy exchanges of free ranging animals may 

be obtained from the other stable isotope 
37 

methodologies. In addition to the use of the 

isotopes 2

H and 18O in the DLW method, natural 

variations in the abundance of 13C and 15N in the 

Arctic environment may be exploited to study diet 

selection in ungulates. 

Haim, A. and J. D. Skinner. 1991. A comparative study 

of metabolic rates and thermoregulation of two African 

antelopes, the steenbok (Raphicerus campestris) and 

the blue duiker (Duiker cephalopus). Journal of Thermal 

Biology 16:145-148. 

The steenbok, a small diurnal antelope is widely 

distributed in the southern African subregion even 

in extreme deserts. The blue duiker is limited in 

its distribution to forests on the eastern coast of 

the subregion. In 1986 – 1987, a comparative 

study on heat production and dissipation was 

carried out in the laboratory using captive animals 

from the zoo of Pretoria, South Africa in order to 

assess the ability of these 2 species to cope with 

dry habitats. Metabolic chambers were used to 

determine oxygen consumption and body 

temperatures were determined using 

thermocouples. Low metabolic rates, a high 

lower-critical point and high overall minimal 

thermal conductance as found in the steenbok 

when compared to the blue duiker seem to be 

important adaptations which help the steenbok to 

conserve water even when exposed to high 

ambient temperatures and, therefore, to inhabit 

extreme arid habitats. 

Hassan, G. A., F. D. El-Nouty, M. H. Salem, M. G. Latif, 

and A. M. Badawy. 1988. Water requirements and 

metabolism of Egyptian sheep and goats as affected by 

breed, season, and physiological status. Pages 65-83 

in Isotope aided studies on livestock productivity in 

Mediterranean and North African countries. 

International Atomic Energy Agency, Vienna, Austria. 

Water requirements and metabolism and some 

physiological and blood characteristics were 

studied in dry non-pregnant Barki and Rahmani 

females and in Baldi goats during spring, summer, 

and winter seasons using titrated water methods. 

The Rahmani sheep showed greater thermal 

discomfort than the Barki during the summer 

season. Goats had higher overall mean total 

protein and albumin levels and lower packed cell 

volumes than sheep. In addition, goats showed the 

highest overall mean total body water and the 

lowest water turnover rate and water loss, 

followed by Barki, then by Rahmani sheep; such 

may also be the order of their tolerance to extreme 

environmental conditions. Pregnancy was 

associated with a significant increase in body 

mass and a decline in the packed cell volume and 

total serum protein, and these changes were 

greater in goats than sheep. They were 

accompanied by significant increases in total body 

water and water turnover rate. All these changes 

were more pronounced during late pregnancy than 

during mid-pregnancy, although the effect of 

stage of pregnancy on total body water did not 

occur in the Barki females. The pregnancy 

induced changes in total protein and water 

turnover rate were greater in spring, while those in 

total body water were greater in winter. The above 

parameters also showed similar changes during 

lactation (particularly during early lactation), but 

lactating animals showed a decrease instead of an 

increase in body mass. Goats showed greater 

reductions in body mass, packed cell volume, and 

water half-life and greater increases in water 

turnover rate than sheep during the spring season. 

Withdrawal of drinking water for 4 days caused a 

reduction in body mass, blood glucose, and 

plasma T3 and T4, and an increase in packed cell 

volume, total serum protein, and plasma 

osmolality. Plasma aldosterone increased slightly 

during dehydration but increased markedly during 

the rehydration period, particularly in the 

Rahmani sheep during the summer season. The 

above parameters changed similarly when the 

animals were starved for 4 days (feed but not 

water was withheld), but total serum protein 

showed a decrease instead of an increase. Changes 

during dehydration were more pronounced in 

summer, while those during starvation were 

greatest in winter. 

Hazam, J. E. and P. R. Krausman. 1988. Measuring 

water consumption of desert mule deer. Journal of 

Wildlife Management 52:528-534. 

The authors developed an accurate (≤1% error) to 

measure water consumption of large, free-ranging 

animals. The system was field tested in the 
38 

Picacho Mountains, Arizona in the summers of 

1985 and 1986. The water consumption of desert 

mule deer (Odocoileus hemionus crooki) was 

recorded. Three collared males visited water 

sources 1.1 times day-1 over 10 days. Deer 

consumed from 1.52 to 6.0 L water catchment 

visit-1 (mean = 3.70, n = 54). Females drank more 

(mean = 4.16, n = 20) than males (mean = 3.55, n

= 24) during late summer (P = 0.019). 

Hecker, J. F., O. E. Budtz-olsen, and M. Ostwald. 1964. 

The rumen as a water store in sheep. Australian 

Journal of Agricultural Research 15:961-968. 

The rumen fluid volume in sheep was measured 

by the method of phenol red dilution. Serial 

determinations made in 22 sheep deprived of food 

and water for up to 8 days showed that the 

greatest decrease in rumen fluid volume occurred 

during the first 2 – 3 days, the magnitude of the 

decrease depending on the initial volume. After 

the third day, the rate of loss of rumen fluid 

became slower as the rumen fluid volume became 

depleted. Sheep deprived of food only gave 

similar results to those of deprived of both food 

and water. This absorption of rumen fluid during 

the first 2 – 3 days of food and water deprivation 

may account for the expansion in plasma volume, 

which has been recorded on the third day. In a 

group of 8 sheep deprived of food and water for 4 

days, the mean rumen volume loss for the period 

amounted to about half the body weight loss. 

These results support the view that in the sheep, 

the water balance of the body proper is kept 

virtually unaltered by fluid drawn from the 

alimentary tract during the first days of water 

deprivation. The animal does not become 

dehydrated, in the physiological sense, until the 

reserve is depleted. For this reason, the rumen 

may be regarded as a water “store” in sheep. 

Hofmeyr, M. D., and G. N. Louw. 1987. 

Thermoregulation, pelage conductance and renal 

function in the desert-adapted springbok, Antidorcas 

marsupialis. Journal of Arid Environment 13:137-151.

The springbok (Antidorcas marsupialis), a gazelle 

of the open, arid plains of southern Africa, can 

survive under hot conditions without access to 

free water. The pelage of the springbok (4.4 ± 1.2 

mm) is thinner than predicted from its body mass 

and has a high conductance (6.7 W m2-1 K-1), 

which increases rapidly with increasing wind 

speed. When prevented from thermoregulating 

behaviorally, it either gains or loses heat rapidly, 

resulting in either thermal panting and sweating or 

a strong shivering response, even at moderate 

ambient temperatures. The unusually thick pelage 

is thought to be an adaptation to facilitate heat 

loss during and after sprinting in this remarkably 

swift antelope. Under natural free-ranging 

conditions, the springbok maintains a fairly 

constant body temperature (37.5 – 41 oC). It 

makes extensive use of orientation of the long axis 

of the body towards the solar beam, thereby 

reducing the profile area exposed to direct solar 

radiation and exploiting areas of the pelage, such 

as the white rump, with a high reflectance value 

(0.72). The kidney has a high relative medullary 

(5.3) and the theoretical potential for 

concentrating urine is high (2,700 - 3,000 mOsm 

kg-1). 

Hoppe, M. G., J. H. Green, J. Hardcastle, P. T. Sanford, 

and P. A. Sanford. 1975. The rumen as a reservoir 

during dehydration and rehydration in the camel. 

Journal of Physiology 254:76-77. 

The rumen function during dehydration and 

rehydration in the camel was studied in covered 

stalls at temperatures ranging from 16 to 27 oC 

and deprived of water for 20 days. The volume 

and outflow of the rumen were measured using 

polyethylene glycol. Food intake remained normal 

at 4 – 5 kg/day for 4 days, then declined to 0.3 kg 

day-1 after 10 days. Plasma osmolality increased 

from 315 to 340 mOsm L-1 and urine osmolality 

from about 1,500 to 2,400 mOsm L-1. Initial 

rumen fluid volume was 14 – 30 L and rumen 

outflow was 51 – 69 L day-1; these values declined 

to 10 – 14 L and 3 – 16 L day-1 after 17 days of 

dehydration. Camels were then allowed to drink 

their fill; after 12 min they drank 34 – 44 L. 

Rumen fluid volume increased and 22 hr later 

remained at about 42 L. Rumen osmolality 

declined to 60mOsm L-1 and 22 hr later it was 140 

mOsm L-1, half its normal value. Rumen 

polyethylene glycol concentrations increased 

indicating that absorption of water through the 
39 

rumen wall exceeded dilution by inflowing saliva. 

Blood osmolality and hemocrit declined 1 hr after 

drinking. The results suggest that the water drunk 

by a dehydrated camel is retained in the rumen for 

24 hr or longer allowing a gradual rehydration and 

adjustment of the body fluid compartments. 

Holtenius, K. 1989. Water and electrolyte transport in 

the ruminant forestomach. Swedish University of 

Agricultural Science Report S-75007. Uppsala, 

Sweden. 

The affects of food deprivation on the 

composition of blood plasma, rumen fluid, rumen 

absorptive function and how differently composed 

intraruminal fluid loads affect absorption of water 

and electrolytes from the rumen in fed and fooddeprived animals were investigated in goats and 

sheep. Ruminal absorption of water was measured 

in water-deprived sheep during rehydration and 

omasal water absorption and fiber digestion were 

compared in normally fed and watered sheep, 

goats, and cattle. Water movements across the 

rumen epithelium were reduced by fooddeprivation and plasma volume was decreased. 

Intraruminal load of volatile fatty acids increased 

blood flow to the ruminal subepithelium and 

stimulated Na absorption in food-deprived goats. 

Water diffusion across the epithelium was also 

increased, however net absorption of water was 

not large enough to restore plasma volume. In 

water-deprived sheep voluntary drinking was 

followed by immediate and substantial absorption 

of water from the rumen. A large portion of fluid 

(43%) leaving the reticulo-rumen through the 

omasal orifice was not retained in the omasal 

body of sheep and bypassed the omasum via the 

omasal sulcus or passed quickly through the 

omasum to the abomasum. Only 17% of the fluid 

bypassed the omasum in goats. 

Hossaini-Hilali, J., S. Benlamlih, and K. Dahlborn. 1994. 

Effects of dehydration, rehydration, and hyperhydration 

in the lactating and non-lactating black Moroccan goat. 

Comparative Biochemistry and Physiology 109A:1017-

1026. 

The effects of water deprivation, rehydration and 

hyperhydration were investigated in 6 black 

Moroccan goats. Mean daily water intake was 46 

± 5 ml kg-1 in lactating and 36 ± 4 ml kg-1 in nonlactating black Moroccan goats, and milk 

production 21 ± 1 ml kg-1. Mean urine excretion 

was 8 ± 2 ml kg-1 body mass in both groups, and 

the daily water losses via evaporation and were 

estimated at 23 ± 3 ml kg-1 during lactation and 28 

± 4 ml kg-1 during non-lactation. Forty-eight hours 

of water deprivation caused a body mass loss of 

9% and 6% in lactating and non-lactating goats, 

respectively, and a drop of 28% in milk 

production with only slight decrease in food 

intake. After rehydration, the elevated plasma 

osmolality as well as Na and total protein 

concentrations returned to basal values within 2 – 

3 hr, indicating a rapid absorption of the ingested 

water, but urine excretion did not increase. After 

hyperhydration (10% of body mass), 46% of the 

load was excreted by the kidneys within 6 hr. In 

conclusion, black Moroccan goats have a low 

water turnover, and they can retain water upon 

rehydration but not store excess water after 

hyperhydration. 

Jarman, P. J. 1973. The free water intake of impala in 

relation to the water content of their food. East African 

Agricultural and Forestry Journal 38:343-351. 

The weekly free water intake of 2 captive impala 

(Aepyceros melampus), living in semi-natural 

circumstances in paddocks in the Serengeti 

National Park, Tanzania, was measured over a 

period of 9 months. Over the same period various 

climatic factors were measured, and intermittently 

the water content of plants in the community from 

which the impala selected their food, was 

determined. It is shown that the daily intake of 

free water was primarily influenced by the water 

content of the food, and secondarily influenced by 

climatic factors as those affected the water content 

of vegetation. Data on water intake are compared 

with those obtained by other workers. Strategies 

which impala may use to minimize their need to 

drink are discussed, and it is shown that their 

pattern of food and habitat selection in the dry 

season confer advantages in water conservation. 
40 

Jessen, C. and G. Kuhnen. 1996. Seasonal variations 

of body temperature in goats living in an outdoor 

environment. Journal of Thermal Biology 21:197-204. 

Blood and brain temperatures were measured 

continuously in three animals on 319, 248, and 

127 days. Over a 30 C range of the 24-h mean of 

air temperature, the 24-h mean of body core 

temperature changed 0.5-C or less. The 24-h mean 

of body core temperature was, in the range 

between 38°C and 39 C. mainly determined by 

non-thermal factors. The 24-h amplitude of body 

core temperature was closely correlated with the 

24-h amplitude of air temperature, and was small 

in winter and large in summer. The relationship 

between blood and brain temperatures was highly 

variable and did not reveal a consistent 

temperature effect within the range of the most 

frequently occurring body core temperatures. 

Jhala, Y. V., R. H. Giles, Jr. and A. M. Bhagwat. 1992. 

Water in the ecophysiology in blackbuck. Journal of 

Arid Environments 22:261-269. 

Blood and urine characteristics of water-deprived 

blackbuck (Antelope cervicapra) were studied in 

Velavadar National Park, India. Blackbuck 

maintained their blood volume during water 

deprivation for 3 days. The blackbuck produced 

highly concentrated urine (specific gravity 1.058) 

and with low (43.3%) moisture content. The 

minimum water requirements of the blackbuck 

were calculated to be 4.26 L 100 kg-1 day-1 at an 

average maximum shade temperature of 48 oC. 

Observations on wild blackbuck indicate the 

importance of preformed water in their forage. 

Wild blackbuck are in a negative water balance in 

summer when ambient temperature is high and 

moisture content of forage is low and are thus not 

independent of drinking water in summer. A 

management technique of supplying drinking 

water based on moisture content of forage is 

suggested. 

Kamal, T. H. 1982. Water turnover rate and total body 

water as affected by different physiological factors 

under Egyptian environmental conditions. Pages 143-

154 in Use of titrated water in studies of production and 

adaptations in ruminants. International Atomic Energy 

Agency, Vienna, Austria. 

The titrated water dilution technique was used to 

determine total body water and water turnover 

rate, which is assumed to be similar to water 

intake, in water buffalo (Bubalus bubalis), Red 

Danish cattle, fat-tailed Osemi sheep, and crossed 

Nubian-Bedouin goats and camels. There was a 

significant effect of species on total body water 

and water turnover rate. The combined data of 

buffalo, cattle, and sheep revealed a significant 

effect of pregnancy on total body water but not on 

water turnover rate. The combined data of buffalo 

and cattle showed significantly lower total body 

water and a higher water turnover rate in lactating 

animals than in females. In buffalo water turnover 

rate was on average 81% higher in summer 

grazing than in spring. It was also 118 and 20% 

higher in summer non-grazing, than in either 

spring or summer grazing, respectively. The 

differences between treatments in females, 

pregnant, and lactating, were significant, except 

between spring and summer grazing in females. 

The total body water on average was 12% higher 

in summer grazing than in spring. It was also 18 

and 5% higher in summer non-grazing than in 

either spring or summer grazing, respectively. The 

differences between treatments in females, 

pregnant, and lactating, were significant except 

between summer grazing and summer nongrazing in lactating cows. 

Kamal, T. hr and M. K. Shebaita. 1972. Natural and 

controlled hot climatic effects on blood volume and 

plasma total solids in Friesians and water buffaloes. 

Pages 103-110 in Isotope studies on the physiology of 

domestic animals. International Atomic Energy Agency, 

Vienna, Austria. 

Blood, plasma, and red cell volumes in ml/kg 

body mass, hemocrit, circulating plasma solids in 

grams, and hemoglobin percentage were 

determined in winter (18.4 oC, 43% relative 

humidity) and summer (29 oC, 55% relative 

humidity) using titrated water in 12 Friesian cattle 

and 11 water buffaloes. These measurements were 

also made on 4 Friesians and 3 buffaloes exposed 

in the climatic chamber to cool (16 oC, 50% 

relative humidity) and hot (32 oC, 50% relative 
41 

humidity) climates for 1 week each. 51Cr-tagged 

red cell technique was used in determining red 

cell volume, which in turn was used with the 

hemocrit to deduce plasma and blood volumes. 

The animals were non-lactating females in the 

season experiment and females in the other 

experiments. Blood, plasma, and red cell volumes 

as well as the circulating plasma solids increased 

in Friesians from winter to summer. In buffaloes 

the vascular fluids increased insignificantly 

whereas the circulating plasma solids did not 

change. Hemoglobin decreased insignificantly in 

Friesians and significantly in buffaloes. In both 

species hemocrit did not change with season. The 

continuous exposure to high ambient temperature 

in the climatic chamber induced a greater heat 

stress. Beside the increase in vascular fluids, the 

hemoglobin and hemocrit decreased and the 

circulating plasma solids increased in both 

species. Sunlight and heat exposure caused 

hemoconcentration in Friesians and hemodilution 

in buffaloes. In Friesians blood and plasma 

volumes decreased and hemocrit increased 

whereas in buffaloes the opposite occurred. The 

circulating plasma solids increased in Friesians 

indicating tissue destruction. One Friesian female 

succumbed to sunstroke as post mortem 

examination revealed subcutaneous burns, brain 

membrane and spleen destruction, and intestinal 

hemorrhage. The data suggests that buffaloes are 

more heat tolerant than Friesians. 

Kamal, T. H, O. Shehata, and I. M. Elbanna. 1972. 

Effect of heat and water restriction on water metabolism 

and body fluid compartments in farm animals. Pages 

95-100 in Isotope studies on the physiology of domestic 

animals. International Atomic Energy Agency, Vienna, 

Austria. 

Eight Ossimi male sheep, five Nubian male goats, 

4 female Friesian cattle, and 4 male water 

buffaloes were maintained in the climatic chamber 

for 3 weeks at 18 oC and 58% relative humidity, 

followed by 1 week outdoors, then by 3 weeks in 

the climatic chamber at 32 oC and 36% relative 

humidity. Total body water and turnover rate were 

determine on the thirteenth day of each climatic 

condition, using titrated water. Extracellular fluid 

using thiosulphate was determined on the 13th and 

20th day of each exposure period. Intracellular 

fluid was determined by difference. Feed and 

water were restricted for 12 hr daily during body 

water and water turnover rate determination; and 

during the other body fluids determination. Body 

fluid compartments were computed on dry body 

mass basis. At high temperature, total body water 

increased in buffaloes and sheep whereas in goats 

and Friesians it did not change. The values for 

goats, Friesians, sheep, and buffaloes were 1,290, 

2,331, 1,239, and 1, 787 ml kg-1 dry body mass, 

respectively at 32 oC. The water turnover rate 

increased with heat exposure in goats, sheep, 

Friesians, and buffaloes. The averages were 120, 

181, 159, and 182 ml kg0.82 daily respectively at 

18 oC, and 228, 321, 312, and 313 ml kg0.82 daily, 

respectively at 32 oC. The heat increased the 

extracellular fluid in sheep and Friesians, and 

increased it insignificantly in buffaloes and goats. 

At 18 oC the averages for goats, Friesians, sheep, 

and buffaloes were 568, 452, 429, and 515-ml kg-1 

dry body mass respectively, whereas at 32 oC they 

were 603, 638, 688, and 879 ml kg-1 dry body 

mass daily respectively. At 32 oC the intracellular 

fluid was significantly higher in sheep and 

buffaloes than at 18 oC. The opposite was true in 

Friesians and goats. In spite of the fact that heat 

increased the water turnover rate in goats (90%) 

and Friesians (96%) more than in sheep (77%) 

and buffaloes (72%), the latter were more able to 

retain water in their bodies than the former in hot 

climates. 

Kamau, J. M. 1988. Metabolism and evaporative heat 

loss in the dik-dik antelope (Rhynchotragus kirki). 

Comparative Biochemistry and Physiology 89A:567-

574. 

Metabolism and evaporative heat loss in 12 adult 

dik-dik antelope (Rhynchotragus kirki) were 

studied in a climatic chamber under laboratory 

conditions. The rate of oxygen consumption, 

respiratory frequency, evaporative water loss, heat 

balance, rectal and surface temperatures were 

determined at ambient temperatures ranging from 

1 to 44 oC. The thermal neutral zone was found to 

be between 24 and 35 oC. Respiratory frequency 

ranged between 27 and 630 breaths min-1. At 

ambient temperature of 44 oC, 95% of heat 

produced by the dik-dik was lost via respiratory 

evaporation. Despite and increase in rectal 
42 

temperatures, cutaneous evaporation did not 

increase. During panting, oxygen consumption 

increased in accordance with the expected Q10

effect, contrary to earlier findings. Measurements 

of circadian rhythm in oxygen consumption 

showed that the minimum (0.42 ml O2 g-1 hr-1) 

occurred at midnight while the maximum (0.78 ml 

O2 g-1 hr-1) occurred at midday. The 24 hr mean 

oxygen consumption was 0.61 ml O2 g-1 hr-1. 

These measurements suggest that in nature, 

determinants other than light may be responsible 

for triggering variations observed in oxygen 

consumption. 

Kamau, J. M. and G. M. O. Maloiy. 1985. 

Thermoregulation and heat balance in the dik-dik 

antelope: a field and laboratory study. Comparative 

Biochemistry and Physiology 81A:335-340. 

Experiments were conducted in the field to study 

the physiological responses of dik-dik 

(Rhynchotragus kirki) to direst solar radiation and 

shade. The results were compared to those 

obtained in the laboratory. The rate of metabolic 

heat production when animals were exposed either 

to the sun or the shade was identical. Dik-dik 

antelopes lost about 50% more heat evaporatively 

when exposed to the sun compared to the shade at 

an ambient temperature of 28 oC in the field or 40 

oC in a climatic chamber. Heat storage in the 

laboratory at 40 oC or at 28 oC in the shade 

accounted for between 30 and 35% of the total 

heat production. The corresponding value in the 

sun was 55%. The net rate of heat gain under the 

sun was four times greater than under shade at 28 

oC or in the laboratory at 40 oC. Behavioral 

mechanisms for avoidance of high insulation must 

constitute important adaptations that the dik-dik 

uses to avoid dehydration and dependence on 

drinking water in the natural environment. 

Kay, R. N. B. 1997. Responses of African livestock and 

wild herbivores to drought. Journal of Arid 

Environments 37:683-694. 

The ways in which herbivores regulate their 

energy and water balance under hot, dry 

conditions are briefly reviewed. Cattle account for 

about two-thirds of the biomass of domestic 

livestock in Africa, but their Eurasian origin 

means that their physiology and grazing behavior 

are not wholly adapted to the natural pastures and 

climate of Africa, especially when drought strikes. 

In general, most herbivores can withstand heat 

and water shortage quite well, provided conditions 

do not become extreme. However, malnutrition 

will inevitably develop as pasture productivity 

declines under drought and overgrazing. This will 

affect most seriously animals that cannot range far 

from water and that depend mainly on droughtsusceptible grasses rather than on more resistant 

shrubs and trees. 

Khan, M. S., P. K. Ghosh, and T. O. Sasidharan. 1978. 

Effect of acute water restriction on plasma proteins and 

on blood and urinary electrolytes in Barmer goats of the 

Rajasthan Desert. Journal of Agricultural Science 

91:395-398. 

The effect of 96 hr water deprivation on plasma 

proteins, blood and urinary electrolyte 

concentrations were studied in Barmer goats of 

the Rajasthan Desert. The total plasma proteins, 

particularly albumin, increased significantly by 

water deprivation. Plasma potassium 

concentrations remained unchanged. The urinary 

K/Na ratio increased considerably. There was a 

decrease in urinary sodium concentration after the 

fourth day of water deprivation. 

Khan, M. S., T. O. Sasidharan, and P. K. Ghosh. 1979. 

Glomerular filtration rate and blood and urinary urea 

concentrations in Barmer goats of the Rajasthan 

Desert. Journal of Agricultural Science 93:247-248. 

Glomerular filtration rate and blood and urinary 

urea concentrations in Barmer goats of the 

Rajasthan Desert were studied in goats receiving 

water ad libitum and goats with restricted access 

to water. Measurement of glomerular filtration 

rate and blood and urine urea concentrations was 

determined using metabolic cages. Water 

restricted animals did not show weight loss or 

animals with ad libitum water. Restricted water 

intake caused an increase in the urea-N 

concentration. There was no decrease in urinary 

urea-N concentration in water-restricted goats. 
43 

Glomerular filtration rate declined to 33% of its 

normal value in water restricted goats. 

King, J. M. 1979. Game domestication for animal 

production in Kenya: field studies of the body water 

turnover of game and livestock. Journal of Agricultural 

Science 93:71-80. 

Field studies were made of titrated water turnover, 

drinking water, and dietary water intake 

throughout the year, in 212 individuals of the 

following species: African buffalo (Synerus 

caffer), dromedary camel, zebu cow, eland 

(Taruotragus oryx), small East African goat, 

fringe-eared oryx (Oryx beisa callotis), and 

Dorper sheep. There were significant differences 

in the water consumed and water turnover 

between species and between seasons. 

Furthermore the species (or season) differences 

were also significantly different for each season 

(or species). The lowest turnover rates were found 

in oryx, then camel, sheep, goat, eland, cow, and 

buffalo, and then expressed in ml L0.82 day-1, 

which was the appropriate metabolic unit for these 

species. The restraints imposed by traditional 

African animal husbandry have drastically 

reduced the natural ability of eland to conserve 

body water but had much less effect on buffalo 

and oryx. The reason appears to be that eland is 

behaviorally adapted to a semi-arid environment, 

whereas a species like oryx is more 

physiologically adapted. 

King, J. M., G. P. Kingaby, J. G. Colvin, and B. R. 

Heath. 1975. Seasonal variation in water turnover by 

oryx and eland on the Galana Game Ranch Research 

Project. East African Wildlife Journal 13:287-296. 

Measurement of total body water and water 

turnover of oryx (Oryx beisa) and eland 

(Taurotragus oryx) were based on the single 

injection of dilution principal using titrated water. 

Under a daylight-grazing regime the water 

turnover varied from 24 to 98 ml kg-1 day-1 in oryx 

and 42 to 121 ml kg-1 day-1 in eland. This large 

seasonal variation was most highly correlated with 

heat load expressed as solar radiation or mean 

ambient temperature. Lack of correlation between 

water turnover and dry matter intake, and low 

correlation with dietary moisture may have been 

due to difficulties in measuring these parameters 

accurately. When preformed water was calculated 

by subtraction of drinking and metabolic water 

from total turnover, it was found to have a 

positive correlation with turnover rate and a 

negative correlation with water drunk. This high 

water turnover was not associated with high 

drinking requirements of other species. The 

relationship between climate, pasture, and water 

turnover, could be upset by changes in the activity 

of the animal from the normal day grazing pattern. 

The results obtained from the domestic game 

animals were used to explain how wild oryx and 

eland could exploit a hot, semi-arid environment 

without drinking. To achieve this, the wild animal 

must obtain most of its nutritional requirements 

between evening and morning, and its water 

requirements during the period of maximum 

relative humidity between midnight and dawn. 

King, J. M., P. O. Nyamora, M. R. Stanley-Price, and B. 

R. Heath. 1978. Game domestication for animal 

production in Kenya: prediction of water intake from 

titrated water turnover. Journal of Agricultural Science 

91:513-522. 

Five male animals of each of the following 

species, zebu cattle, eland (Taruotragus oryx), 

small East African goat, fringe-eared oryx (Oryx 

beisa callotis), and Dorper sheep, were penned, 

and their water intake measured and metabolic 

water production estimated. The figures for water 

input were compared with simultaneous 

measurements of body water turnover by liquid 

scintillation counting of titrated water in plasma, 

following dioxane precipitation. It was found that 

the resultant regression was sufficiently linear 

with the intercept near zero to justify the use of a 

ratio to predict input from turnover. The titrated 

water turnover overestimated the water input by 

an amount approximately equal to the 

overestimate of body water pool by the titrated 

water space. Although there was a considerable 

amount of variation in individual ratios that could 

not be explained, there was no significant 

difference in the mean ratios between species. 

King, J. M. and V. A. Finch. 1982. Value and limitations 

of using titrated water for predicting body composition 

and water intake in the African zebu. Pages 57-67 in 
44 

Use of titrated water in studies of production and 

adaptations in ruminants. International Atomic Energy 

Agency, Vienna, Austria. 

The titrated water space gave a 10% overestimate 

of the total body water pool obtained by dissection 

and drying, using 12 Zebu steers. The decrease in 

percent body fat between a weight of 220 and 190 

kg was significantly related to an increase in the 

percent body water pool. The percent body fat 

could be predicted from the percent titrated water 

space, but the approach was considered 

questionable, particularly outside the bounds of 

these trials. A comparison between water input 

from food and drink plus calculated metabolic 

water and titrated water turnover was made in 6 - 

12 Zebu steers on 4 occasions, for 42 individual 

comparisons. There was a shortfall of 11% 

between input and turnover even after correction 

of the overestimate of the body water pool by 

tritium. The shortfall could be accounted for by 

respiratory water exchange, which was estimated 

to represent 10% of the total water input. 

Although the mean ratio of input: titrated water 

turnover was 0.96 ± 0.022, there were significant 

differences between individual ratios and 

experiments. The main reason for the difference 

was probably due to non-steady-state conditions 

during the periods of estimating water turnover. 

Errors in the prediction of total water input from 

titrated water turnover will be the rule rather than 

the exception for tropical herbivores in semi-arid 

areas where intermittent watering is practiced 

unless the experiment is very carefully designed. 

Knox, K. L., J. G. Nagy, and R. D. Brown. 1969. Water 

turnover in mule deer. Journal of Wildlife Management 

33:389-393. 

Water turnover and kinetics were determined in 

11 female mule deer (Odocoileus hemionus) 

ranging in weight from 18 to 42 kg using titrated 

water. The percent body water, turnover, half 

time, and flux of 9 deer maintained in nonconfined captivity were 67%, 11% day-1, 6.5 days, 

and 74 ml kg-1 day-1, respectively. The values for 

the same parameters in 2 closely confined deer 

were: 70%, 31% day-1, 2.3 days, and 216 ml kg-1 

day-1, respectively. Dry matter consumption was 

65g kg0.75 and water consumption was 140 g kg0.75 

in the non-confined deer. The data suggest that 

water kinetics in non-confined mule deer is not 

essentially different from other animals. 

Kuhnen, G. 1997. Selective brain cooling reduces 

respiratory water loss during heat stress. Comparative 

Biochemistry and Physiology 118A:3:891-895. 

Terrestrial mammals developed several 

mechanisms to reduce water loss to counteract 

water shortage. One avenue of water loss is the 

evaporative heat loss by sweating and panting, 

which increases with body temperature. Sweating 

and panting are activated by temperature signals 

of the body, whereby the brain is the most 

important site in generating temperature signals. 

Goats, like other artiodactyls, can cool their brains 

selectively below the temperature of the trunk 

core. The aim of the present study is to determine 

whether an inhibition of the selective brain 

cooling (SBC) mechanism will increase 

substantially the respiratory evaporative water 

loss during heat stress due to the higher brain 

temperature. The inhibition of SBC was 

performed by increasing brain temperature 

experimentally at the same rate as trunk 

temperature by means of extracorporeal heat 

exchangers. These experiments without SBC 

resulted in higher respiratory evaporative water 

loss compared to experiments with normal SBC. 

Eighteen experiments in two conscious goats had 

shown that at a trunk temperature of 40°C the 

respiratory water loss was reduced on average by 

29 g/hr (0.7 l/day) due to the effect of SBC. This 

amount of water corresponds to about one third of 

the general water requirements. In conclusion, 

SBC substantially reduces the water loss in goats 

during heat stress and consequently improves 

survival chances during water shortage. 

Lackey, M. N., E. B. Belknap, M. D. Salman, L. 

Tinguely, and L. W. Johnson. 1995. Urinary indices in 

llamas fed different diets. American Journal of 

Veterinary Research 56: 859-865. 1995. 

Indices of renal function and damage were 

measured in 12 healthy male adult llamas (Llama 

glama) fed a diet of mixed alfalfa/grass hay 

(mixed hay) and water ad libitum. Using a 

collection bag fitted over the preputial area, urine 
45 

samples were collected at 6, 12, and 24 hours. 

Serum samples were obtained concurrently to 

determine endogenous creatinine clearance (CL), 

total (TE) and fractional excretion (FE) of 

electrolytes (Na, K, Cl, P), electrolyte CL, urine 

and serum osmolality, urine enzyme activities 

(glutamyltransferase and N-acetyl - Dglucosaminidase) and urine protein concentration. 

Urine production was quantified. Three months 

later, 10 of the 12 llamas were fed a grass day diet 

and water ad libitum. Similar samples were 

obtained and similar measurements were made. 

Urine production was higher when the llamas 

were fed the mixed hay diet. Total urine volume 

for llamas fed mixed hay ranged from 628 to 

1,760 ml day-1, with a median of 1,307.5 ml day-1, 

compared with a range of 620 to 1,380 ml day-1, 

compared with a range of 620 to 1,380 ml day-1

and a median of 927.50 ml day-1 for llamas fed 

grass hay. Median urine osmolality was higher in 

llamas fed mixed hay (1,906 mOsm kg-1 of body 

mass, with a range of 1,163 to 2,044 mOsm kg-1). 

Creatinine CL did not vary significantly over time 

for either diet. Median creatinine CL was higher 

for llamas fed mixed hay, compared with llamas 

fed grass hay 0.78 ml min-1 kg-1, with a range of 

0.20 to 1.83 ml min-1 kg-1 vs. 0.45 ml min-1 kg-1, 

with a range of 0.13 to 3.17 ml min-1 kg-1. 

Clearances for K and Cl varied significantly 

among the periods. However, median CL for Na 

and P did not vary over time for either diet. 

Overall values for these electrolytes in llamas fed 

mixed hay and grass hay diets were: NaCl 0.001 

and 0.002 ml min-1 kg-1 and PCL, 0.0006 and 

0.0004 ml min-1 kg-1, respectively. The FE rates of 

K, Cl, and P did not vary significantly over time 

for either diet. Median respective FE for these 

electrolytes in the llamas fed mixed hay and grass 

hay include: FEk, 84.90 and 63.10%; FeCl, 0.85 

and 1.30%; and PFe 0.10 and 0.10%. Fractional 

excretion of Na varied over time for both diets 

and could not be expresses accurately as an 

overall median. Median respective TE of 

electrolytes for llamas fed the mixed hay and 

grass hay diets were: TE Na, 0.007 and 0.03 mEq 

kg-1 hr-1; TE Cl, 0.04 and 0.06 mEq kg-1 hr-1; and 

TE P, 0.0002 and 0.00 mg kg-1 hr-1; TE K varied 

significantly (P<0.05) over time. Urine N-acetylβ-D-glucosaminidase activity was influenced by 

an interaction between diet and time. Median 

urine protein concentration was 26.0 mg dL-1, 

with a range of 11.0 to 73.0 mg dL-1 for llamas fed 

mixed hay, and was 28.0 mg dL-1, with a range of 

16.0 to 124.0 mg dL-1 for llamas fed grass hay 

Laden, F. S., L. Nehmadi and R. Yagil. 1987. 

Dehydration tolerance in Awassi fat-tailed sheep. 

Canadian Journal of Zoology 65:363-367. 

Young Awassi sheep were subjected to 5-day 

periods of complete water restriction in metabolic 

cages. During water deprivation there were steady 

declines in food intake and faces and urine 

excretion. The blood hemocrit and urine and 

plasma osmolalities increased. There was a 

decline in blood and fecal water. As dehydration 

progressed, urinary excretion of osmotically 

active substances was greatly reduced. When 

drinking water was presented following 5 days of 

restriction it took 24 hr to replace water losses and 

for urine to be excreted. Fecal water did not return 

to normal within 24 hr. The Awassi sheep were 

capable of withstanding dehydration. The 

dehydrated sheep relied on fecal and renal water 

conservation to survive. Awassi sheep do not 

rapidly replenish water losses, nor do they rapidly 

reabsorb water, making their stay at water holes 

longer than goats. 

Langman, V. A., G. M. O. Maloiy, K. Schmidt-Nielsen, 

and R. C. Schroter. 1978. Respiratory water and heat 

loss in camels subjected to dehydration. Journal of 

Physiology 278:P35. 

Ambient air, rectal, and expired air temperatures 

and humidities under moderate heat load and 

dehydration were measured in 2 camels. 

Temperatures were measured using 

thermocouples and water content of expired air 

was measured with a dew point hygrometer 

attached to a heated face mask and air line. At 

night expired air tended towards ambient 

temperatures; during the day it tended towards 

rectal temperatures but was significantly lower. 

Expired air was always fully saturated. Camels 

recovered about 70 and 25% of the potential 

respiratory water loss during the night and day, 

respectively. Daytime respiratory heat loss was 

twice the rate at night. Heat and water exchange 

occurred within the turbinates of the nose as 

measured by temperature profiles. 
46 

Langman, V. A., G. M. O. Maloiy, K. Schmidt-Nielsen, 

and R. C. Schroter. 1979. Nasal heat exchange in the 

giraffe and other large mammals. Respiration 

Physiology 37:325-333. 

The respiratory air of the giraffe (Giraffa 

camelopardalis) is exhaled at temperatures 

substantially below body core temperature. As a 

consequence, the water content of the exhaled air 

is reduced to levels below that in pulmonary air, 

resulting in substantial reductions in respiratory 

water loss. Measurements under outdoor 

conditions showed that at an ambient temperature 

of 24 oC, the exhaled air was 7 oC below body 

core temperature, and at ambient temperature of 

17 oC, the exhaled air was 13 oC below body core 

temperature. The observations were extended to 

two additional species of wild (wildebeest 

[Connochaetes taurinus] and waterbuck [Kobus 

ellipsiprumus]) and four species of domestic 

ungulates (sheep, donkey, goat, and cow). All 

these animals exhaled air at temperatures below 

body core temperature. The average amount of 

water recovered due to cooling of the air during 

exhalation, calculated as percent of the water loss 

that would occur if air were exhaled at body core 

temperature, amounted to between 24 and 58%, 

the average value for the giraffe being 56%. 

Lautier, J. K., T. V. Dailey and R. D. Brown. 1988. 

Effect of water restriction on feed intake of white-tailed 

deer. Journal of Wildlife Management, 52:602-606. 

The effect of water restriction on feed intake of 

white-tailed deer was studied at Caesar Kleberg 

Wildlife Research Institute, Texas A&M 

University, Kingsville, Texas. Nine male whitetailed deer (Odocoileus virginianus) were held in 

pens and offered feed and water ad libitum for 3 - 

4 days, and measured intake of both daily. We 

provided separate groups (3 x 3 balanced, simple 

crossover design) 33, 67, and 100% of ad libitum 

water intake for 4 days. Mean dry matter intake 

(DMI) (g kg-0.75 body mass) for 3 - 4 days 

prerestriction was compared to each of the 4 days 

on restriction. Dry matter intake decreased (P < 

0.01) for deer receiving 33% ad libitum water 

intake on days 3 and 4. One deer refused feed on 

day 4. There was a difference (P< 0.05) in mean 

DMI on day 3 between the group receiving 100% 

of ad libitum water and the group that received 

33% of ad libitum water. Differences in DMI 

existed on day 4 among all 3 groups (P<0.05). 

The group receiving 33% of ad libitum water lost 

more weight than the other groups (P < 0.05). 

Because of lower than expected body water losses 

by the water-restricted animals, it appears that 

white-tailed deer possess some degree of 

physiological adaptation to dehydration. High 

daily maximum temperatures (36 oC) may have 

exacerbated the effect of water restriction on 

DMI. Because of high temperatures and frequent 

summer droughts in southern Texas, the need for 

adequate water for white-tailed deer may be 

critical. 

Longhurst, W. M., N. F. Baker, G. E. Connolly, and R. 

A. Fisk. 1970. Total body water and water turnover in 

sheep and deer. American Journal of Veterinary 

Research 31:673-677. 

The total body water and body water turnover in 

Columbian black-tailed deer (Odocoileus 

hemionus columbianus) and domestic sheep were 

compared in winter and summer by testing with 

tritium oxide. There was a significant difference 

in water turnover in both species when data 

obtained in the winter were compared to those 

obtained in the summer. In addition, there was a 

significant difference in water turnover between 

the 2 species in winter and summer. Deer had a 

larger body water pool in relation to body mass 

than did sheep, but rate of body water turnover in 

deer was slower in winter and summer. The mean 

body water pools of sheep in winter and in 

summer were 53.3 and 46.0% of body mass. The 

water flux in sheep was 0.102 and 0.14 L/kg/day 

in winter and in summer, respectively. 

Comparable values in deer were 0.053 and 0.104 

L kg-1 day-1. 

Macfarlane, W. V. 1965. Water metabolism in desert 

ruminants. Pages 191-199 in A. K. McIntyre and D. R. 

Curtis, editors, Studies in physiology. Springer-Verlag, 

New York, New York, USA. 

Total body water, water turnover, and plasma 

volume were studied in camel, cattle, sheep, 

goats, and red kangaroos (Marcopus rufus) using 
47 

thiocyanate and titrated water. Camels and cattle 

from hot arid regions had body water contents of 

66 – 85% whereas cattle from cooler regions had 

body water contents of 68%. Plasma volume of 

animals from arid regions was approximately one 

third that of animals from cooler areas. Water 

turnover rates were also higher in animals from 

arid areas than in those from cooler regions. 

Interspecific and individual differences in these 

parameters are also discussed. 

Macfarlane, W. V. and B. Howard. 1972. Comparative 

water and energy economy of wild and domestic 

mammals. Symposia of the Zoological Society of 

London 31:261-296. 

Over 99% by number of the molecules present in 

a ruminant are water. Measurement of titrated 

water turnover provides ecophysiological 

information on the water metabolism of breeds, 

species or genera, compared in the field while 

exposed to the same environment. The powerful 

effects of solar radiation on water demand in the 

desert are integrated with those of air temperature 

and food supply by this approach. Water turnover 

is influenced by age, environmental temperature, 

food supply, density, lactation, and behavior. Yet 

the intrinsic rate at which each species uses water 

brings about the same rank order of water 

turnover among those species in different 

environments. This rank order for water turnover 

is closely correlated with the metabolic rate or 

oxygen turnover, which is high in some desert 

animals with high water turnover (eland 

[Taurotragus oryx], cattle, reindeer [Rangifer 

tarandus]), and low in other (camel, goat, oryx 

[Oryx beisa], musk ox [Ovibos moschatus]) which 

economize water. Other correlated variables are 

the rates of pulmocutaneous evaporation, and 

movement of water from gut to blood, which are 

rapid in animals with high rates of oxygen and 

water metabolism, low in others. Low rates of 

movement of water and energy through animals 

allow them longer survival in, and better 

adaptation to the desert. Sensitivity to vasopressin 

is high in desert mammals with low water 

turnover and low in those with high water 

demands. The recent distribution of mammals in 

arid areas shows anomalies of ecophysiology that 

could be explained if the functional evolution of 

some mammals took place in non-arid regions, 

followed by migration into the desert without 

modification of their functions. Others, evolved in 

the desert, remain there when high-rate animals 

perish. 

Macfarlane, W. V., B. Howard, and B. D. Siebert. 1967. 

Water metabolism of merino and Leicester sheep 

grazing saltbush. Australian Journal of Agricultural 

Research 18:947-958. 

Water metabolism of merino and Leicester sheep 

grazing saltbush were studied using titrated water. 

During late summer, Border Leicester wethers 

running with Merinos on a pure Atriplex 

nummularia stand turned over 10.6 to 17.5 L 

(mean = 13.7 L) of water daily, and diluted the 

sodium and potassium ingested to less than 1000 

mOsm/L in the urine. Leicesters used 46% more 

water than Merinos as L day-1, and 71% more as 

ml kg0.82 day-1. The two breeds produced similar 

urine concentrations. The sheep showed a wide 

variation in response and their individual water 

turnovers while feeding on A. nummularia and A. 

vesicaria ranged from 120 to 833 ml kg0.82 day-1. 

This suggests differences in functional types of 

adjustment to saltbush associations. On a 

Danthonia community Leicesters again turned 

over more water than Merinos but only about half 

as much water was required as on saltbush. 

Merinos grazing on A. vesicaria over 2 years 

maintained good condition with half the water 

intake of Merinos on A. nummularia, although the 

2 species of saltbush had similar sodium and 

potassium contents. Total body water increased 

with water turnover rate on saltbush. Plasma 

sodium concentration was inversely related to 

water turnover, extracellular volume, and total 

body water on saltbush pastures. The content of 

extracellular sodium was, however, greatest in the 

sheep with the least sodium in the diet. 

Macfarlane, W. V., B. Howard, and B. F. Good. 1974. 

Tracers in field measurements of water, milk, and 

thyroxine metabolism of tropical ruminants. Pages 1-23 

in Tracer Techniques in Tropical Animal Production. 

International Atomic Energy Agency, Vienna, Austria. 
48 

Productive animals in the tropics may need to be 

adapted to hot-wet, or to alternating hot-wet and 

hot-dry environments. In both climates water is 

important for metabolism and for cooling. 

Isotopes are useful in measuring content and the 

turnover rate of water. Water content (3

H2O) gives 

field information on body solids, fat, and protein 

content in relation to pasture and metabolic drain 

(as in starvation or lactation). Water turnover is 

closely linked with energy turnover. There is, 

among domestic stock, a hierarchy of turnover 

rates: a) high water turnover is found in tropical 

mammals such as buffalo, Banteng, cattle, eland 

(Taurotragus oryx), and pig; b) there are 

intermediate rates of water use in sheep, goats, 

and wildebeest (Connocaetes taurinus); c) low 

rates of energy and water turnover occur in drycountry animals like the camel or oryx (Oryx 

beisa). 3

H2O turnover relates to food intake and as 

more water is taken more food is eaten. But the 

rank order of animals for water turnover remains 

similar in different conditions, with different food 

supplies. Production of wool or milk is associated 

with proportional water turnover, and has a 

genetic basis. Water turnover of lambs or calves is 

a direct function of milk intake and 3

H2O yields 

both body solids increments, not necessarily 

associated with thermodynamic efficiency. 

Because metabolic rate is high in animals with 

high water turnover, it seemed likely that 

thyroxine would be related to those functions. 

Plasma bound iodine is (131 I or 125I) very different 

in concentration in different genera and unrelated 

to rate functions. In the field, ruminant plasma 

bound iodine is high in summer, low in winter. 

Thyroxine secretion rate is low in large genera 

and high in small genera of ruminants. Secretin is 

higher in winter than summer. It is influenced 

greatly by food intake, rising with increasing food 

turnover and water turnover. Thyroxine seems to 

moderate intrinsic metabolic rates rather than set 

the rate of metabolism. 

Macfarlane, W. V., B. Howard, and G. M. O. Maloiy. 

1972. Titrated water in field studies of ruminant 

metabolism in Africa. Pages 83-93 in Isotope studies on 

the physiology of domestic animals, International 

Atomic Energy Agency, Vienna, Austria. 

Titrated water was used to measure turnover of 

adult ruminants in Kenya. In the suckling young, 

water turnover by titrated water is a direct 

measure of milk intake. A hierarchy of ruminant 

ecophysiology of water and energy was measured 

in a number of environments in Kenya with 

groups of species grazing together. In the 

equatorial desert of Northern Frontier District, the 

rank order for titrated water turnover was: Boran 

cattle (347 mg kg0.82 day-1), twice the rate of 

Ogaden sheep (197 mg kg0.82 day-1), with Somali 

goats (185 mg kg0.82 day-1) and dromedaries (192 

mg kg0.82 day-1) at the lowest turnover rates. On 

the hot-wet equatorial pastures, the rank order of 

sheep was Karakul, with the greatest turnover, 

then Merino, and Dorper sheep the lowest. Upland 

equatorial grasslands at Athi River, Boran cattle 

(224 mg kg0.82 day-1) grazed with eland 

(Taurotragus oryx) (213 mg kg0.82 day-1) and had 

almost identical rates of water use. Wildebeest 

(Connocaetes taurinus) (137 mg kg0.82 day-1) and 

hartebeest (Alcelaphus buselaphus) (116 mg kg0.82

day-1) turned over at half the rate of eland in the 

same environment. Thus eland appear to be cattlelike antelope, whereas the wildebeest and 

hartebeest were more like sheep in their rate of 

water use. The oryx (Oryx beisa) (70 mg kg0.82 

day-1) is like a camel in turnover rate. In 

equatorial temperate upland pastures at Muguga, 

identical twin cattle agreed within 2% in the water 

turnover rates of twin pairs of cattle grazing 

together. Domestic cattle s types of twin used 16-

38% more water than Zebu cattle. The identical 

twin functions indicate a close genetic control of 

the rate of water use on a given food type. 

Domestic species grazing the lush grasses showed 

a rank order of water like that found in the 

Northern Frontier District. Domestic cattle used 

more water (338 mg kg0.82 day-1) than Zebu cattle 

(284 mg kg0.82 day-1). The rate of use by cattle was 

twice that of Mosai sheep (195 mg kg0.82 day-1). 

Somali goats (137 mg kg0.82 day-1) used the least 

water in this environment. The Somali donkey 

(314 mg kg0.82 day-1) had a water use rate between 

those of the cattle species. Therefore similar 

hierarchies were maintained in different 

environments. 

Macfarlane, W. V., B. Howard, and R. J. H. Morris. 

1966. Water metabolism of merino sheep shorn during 
49 

summer. Australian Journal of Agricultural Research 

17:219-225. 

Ten merino wethers in the dry subtropical region 

of “Gilruth Plains”, Queensland, Australia were 

shorn in November during a period of sunshine 

with maximum temperatures between 36 and 38 

oC. The content, distribution, and turnover of 

water were estimated using titrated water before 

and after shearing. There was no significant 

change in total body water but the thiocyanate 

space increased by 12%, the plasma volume by 

17%, and the plasma proteins were diluted by 

17% after shearing. Water turnover rose from 81.5 

to 159ml kg-1 day-1. There was a correlation (r = 

0.68) between the increase in respiratory rate that 

took place when the sheep were standing in the 

sun and the increase in water turnover during the 

same period. An average increment of 1,550 kcal 

day-1 in heat load from insulation occurred as a 

result of the removal of fleece during exposure to 

summer sun. The greater water turnover from 

evaporative cooling was associated with increased 

extracellular fluid space.

Macfarlane, W. V., B. Howard, H. Haines, P. J. 

Kennedy, and C. M. Sharpe. 1971. Hierarchy of water 

and energy turnover of desert mammals. Nature 

234:483-484. 

The uninhibited intake of food and water by 

cattle, sheep, goats, camel, eland (Taurotragus 

oryx), buffalo (Bubalus bubalis), wildebeest 

(Connochaetes gnou), kongoni (Alcelaphus 

buselaphus), oryx (Oryx beisa), moose (Alces 

alces), reindeer (Rangifer tarandus), and musk 

oxen (Ovibos moschatus) were measured. Buffalo 

had the highest water turnover, then cattle. In 

summer, the highest water turnover rates occurred 

in cattle, followed by sheep, then goats, and 

camels the least. Of the antelope, eland and zebu 

cattle were approximately equal in water turnover, 

while kongoni and wildebeest are comparable 

with sheep, at half the rate of eland, and an oryx 

used water at a lower rate than camels. Of the 

arctic species, reindeer had water turnover rates as 

high as cattle, the moose was slightly lower than 

reindeer, but twice that of sheep and goats, while 

the musk oxen had water turn over rates as low as 

camels. The metabolic rate of bovids follow the 

same rank order as water turnover. 

Macfarlane, W. V. and B. D. Siebert. 1967. Hydration 

and dehydration of desert camels. Australian Journal of 

Experimental Biology 45:29 (abstract). 

During winter, water turnover of camels is low, at 

37 to 40 ml kg-1 day-1, and this rises during the 

summer to 70 to 90 ml kg-1 day-1. Because of the 

fat deposit in the hump, the body water content 

rarely rises above 75% of body mass. Without 

water in the summer, the camel loses weight at 

2% day-1 and persists in functional order for 10 to 

15 days. During slow dehydration the packed cell 

volume does not change, although the 

extracellular and plasma volume decreases by 15 

to 20%. At more rapid rates of dehydration (2.5% 

day-1) greater extracellular loss occurs, but there is 

deferential sparing of plasma volume and a high 

plasma albumin concentration is retained, while 

gut and cell water is drawn upon. Urine flow 

reaches 1 - 2 ml/min and vasopressin (0.1 mμ kg1

) increases potassium and water excretion. 

Glomerular filtration falls to one-quarter normal 

the normal rate and urine reaches 3.1 osm L-1. 

Fecal water is reduced to 40% of fecal weight. On 

rehydration the camel takes in 54% to 66% of the 

weight lost within 20 min. There is a reduction in 

urine flow to 0.2 ml min-1 and reduction in sodium 

and potassium excretion. Packed cell volume 

increases for some hours then decreases, the slow 

titrated water uptake from the gut does not reach 

equilibrium for nearly 18 hours. After one day 

urine flow as electrolytes are removed from the 

plasma to the gut. At these higher rates of urine 

flow, the camel responds to 1 μU kg-1 vasopressin 

by reduction in urine flow. 

Macfarlane, W. V, C. H. S. Doling, and B. Howard. 

1966. Distribution and turnover of water in Merino 

sheep selected for high wool production. Australian 

Journal of Agricultural Research 17:491-502. 

Estimates of the distribution of body water and the 

rate of water turnover were made on Merino 

females in southwestern Queensland, Australia 

during January and November. January 

measurements were made while pasture 
50 

conditions were lush green following good rains 

and November measurements were made when 

pastures were dry following several months with 

low rainfall. Females were selected from a flock 

that had been selectively bred from high wool 

production and from a control flock where all 

animals were allowed to breed. Plasma volume, 

extracellular volume, total body water, plasma 

protein, and water turnover per day were 

estimated. Body fluid compartments, as ml/kg 

body mass, were greater during the wet than 

during the dry period. Plasma volumes were 

significantly greater in January than in November 

by 10.3% for the selected females and 18.2% for 

control females. Estimates of extracellular volume 

showed a similar difference between months 

(15.4% for selected females and 17.4% for control 

females). January measurements of total body 

water exceeded November observations by 9.6% 

in selected females and 11.2% in control females. 

The values for plasma volume, extracellular 

volume, and total body water did not differ 

between selected females and control females. 

The daily turnover rate of water in ml kg-1 body 

mass was greater in January than in November by 

30% for selected sheep and 51.1% for control 

sheep. 

Macfarlane, W. V., R. J. H. Morris and B. Howard. 

1958. Heat and water in tropical Merino sheep. 

Australian Journal of Agricultural Research 9:217-228. 

The relation between environment and the water 

intake and output of young Merino sheep living in 

hot dry tropics was studied for 3 years in Julia 

Creek, Australia. Long (3 cm) wool insulates 

sheep from hot summer temperatures. The 

respiratory rates of sheep shorn of wool during the 

summer were more than twice those of unshorn 

sheep standing in the sun. Evaporative cooling, by 

panting, increases water demand, and in summer 

sheep drank an average of 12 times as much water 

as in winter, when they drank 7.3 ml kg-1 day-1. 

Water intake was closely related to respiratory 

rate. Urine output was lower in summer than in 

winter. 

Macfarlane, W. V., R. J. H. Morris, B. Howard, J. 

McDonald and O. E. Budtz-Olsen. 1961. Water and 

electrolyte changes in tropical Merino sheep exposed to 

dehydration during summer. Australian Journal of 

Agricultural Research 12:889-912. 

During 3 summers field studies were made of 

Merino wethers deprived of water while exposed 

to sun and to maximum air temperatures ranging 

from 29 – 42 oC at Julia Creek, Australia. 

Evaporative cooling determined the rate and 

extent of water and electrolyte changes and 

produced a different pattern each year. Control of 

body temperature failed when 31% of body mass 

was lost by the end of 10 days without water. In 

hotter weather 5 days without water caused a 25% 

loss of body mass and in some sheep irreversible 

circulatory failure. In the course of dehydration, 

after initial increase, the plasma and extracellular 

volume decreased up to 45% while concentrations 

of hemoglobin and plasma protein increased by 

60%. In the plasma, potassium and sodium 

concentration increased less than that of 

hemoglobin. When 25% or more of weight was 

lost plasma urea concentration rose to 136 mg 100 

ml-1. Plasma osmolarity in some sheep reached 

490 mOsm L-1 after 10 days. Urine volume fell 

after 2 days without water, and in a hot season 

less than 100 ml day-1 was passed on the fourth or 

subsequent days. Concentrations increased over 

the first 4 – 5 days, reaching a maximum of 3.8 

mOsm L-1, then declined. Between half and twothirds of the osmolarity was accountable to 

sodium and potassium salts. In rapid dehydration, 

more sodium was excreted than potassium. There 

was reduced sodium excretion when water was 

ingested after dehydration. Renal function studies 

in females indicated that filtration, renal plasma 

flow, and glucose reabsorption was reduced to 

half after 5 days without water in the heat. The 

chance of survival in dehydration appears to be 

increased by low rates of water loss in the first 3 

days, together with high sodium and low 

potassium excretion. A full rumen, containing 

water up to 13% of body mass, could provide all 

the extracellular fluid loss. More than half of the 

weight loss appears, however, to come from 

intracellular sources. Extracellular fluid was 

drawn upon to a greater extent when the rate of 

dehydration was rapid, than in the cooler periods 

of slow weight loss. Survival in the sun without 

water depends on insulation, water conservation, 

water reserves in rumen and extracellular fluid, 
51 

the ability to adjust electrolyte concentrations, and 

the ability to maintain circulation with lowered 

plasma volume. 

Macfarlane, W. V., R. J. H. Morris, B. Howard and O. E. 

Budtz-Olsen. 1959. Extracellular fluid distribution in 

tropical Marino sheep. Australian Journal of Agricultural 

Research 10:269-286. 

Merino females and wethers maturing from 12 to 

53 months of age were studied for 3.5 years at 

Julia Creek, Australia during summer and winter. 

Measurements were made of plasma volume and 

extracellular volume, plasma proteins, 

hemoglobin, hemocrit, and plasma electrolytes via 

blood extractions. The range of normal values for 

these parameters in healthy sheep varied widely. 

Large changes took place in the fluid volumes 

during the period of investigation; the changes 

appeared to be independent of seasons but to a 

great extent determined by nutrition. Poorly 

nourished sheep as a whole had increased 

extracellular fluid space, and the space shrank 

again on improved pasture. Age and sex did not 

influence the fluid volumes. Lactation was 

associated with an increase in fluid spaces, and 

year feeding with a decrease. Non-tropical sheep 

introduced from 30o S latitude during winter had 

similar fluid volumes to the tropical sheep when 

investigated 2 months after their arrival. Tropical 

Merinos at any age or season had larger plasma 

volumes than sheep kept in laboratory pens in 

Brisbane or in Melbourne, Australia. 

Maloiy, G. M. O. 1970. Water economy of the Somali 

donkey. American Journal of Physiology 219:1522-

1527. 

Water balance, food intake, volume, and 

concentration of urine and changes in body mass 

were examined in the 7 Somali donkeys subjected 

to heat stress and dehydration while held in 

metabolic cages. The effects of an ambient 

temperature of 22 oC or changes between 22 and 

40 oC at 12-hr intervals and a level of dehydration 

causing 15% loss of body mass at each of these 

temperatures on food intake and digestion were 

investigated. Dehydration at each environmental 

temperature depressed food intake and increased 

apparent digestibility of dry matter, but a periodic 

heat load without dehydration had no effect on 

either parameter. The animal’s appetite failed 

altogether when 20 – 22% of its initial body mass 

had been lost. Fecal and evaporative routes were 

the main avenues of water loss in all experimental 

conditions. Evaporative water loss was reduced by 

65 and 52%, respectively, when animals were 

dehydrated at 22 and 40 oC. The donkey can 

survive a loss of water corresponding to 30% of 

its original body mass even at ambient 

temperature of 40 oC, and can drink in 2 – 5 min 

enough water (24 – 30 L) to restore its deficit. 

Even when water was freely available, urine 

volume was low (0.7 – 1.2 L day-1). The donkey’s 

kidney was not able to excrete a highly 

concentrated urine; 1,440 – 1,545 mOsm kg-1

water was the maximum osmolality, with urea 

contributing 300 – 410 mM. When the donkey 

was offered various concentrations of NaCl 

solution as its sole source of drinking water, the 

maximum level accepted by the animal was 0.75 – 

1.00% NaCl. 

Maloiy, G. M. O. 1971. Temperature regulation in the 

Somali donkey (Equus asinus). Comparative 

Biochemistry and Physiology 39A:403-412. 

In controlled laboratory experiments the 

metabolic rate, body temperature, respiratory, 

sweat, and heart rates were measured in adult 

Somali donkeys. At high ambient temperatures 

(40 – 50 oC) the sweating rate rose to 145 g water 

m2-1 hr-1 and the respiratory rate to approximately 

130 min-1. In cool conditions (10 oC) the 

metabolic rate rose to approximately 5 ml oxygen 

kg-1 min-1 from a value in thermal neutrality (22 – 

32 oC) of 4 ml kg-1 min-1. Between ambient 

temperatures of 5 and 50 oC the rectal temperature 

ranged from 35 to 39 -1C. 

Maloiy, G. M. O. 1972. Renal salt and water excretion 

in the camel (Camelus dromedarius). Symposia of the 

Zoological Society of London 31:243-259. 

A study of the glomerular filtration rate and renal 

sale and water excretion was studied in the camel 

under a variety of controlled experimental 

conditions. Changes in urine flow and 
52 

concentration and insulin clearance during 

dehydration and salt loading were measured. Slow 

dehydration at 0.8% day-1 weight loss, involving a 

gradual reduction in daily water intake until body 

mass decreased by 20 - 22%, caused a 57% 

decrease in urine flow and a 30% reduction in the 

glomerular filtration rate. Salt loading increased 

glomerular filtration rate and urine flow by about 

52 and 103%, respectively. In dehydrated and in 

salt loaded camels, respectively 99.8% and 99.2% 

of the water filtered at the glomerulus was 

reabsorbed. The observed changes in urine flow 

appeared to be brought about by alteration in 

glomerular filtration rate and renal tubular water 

reabsorption. Urine and plasma osmolality 

increased during salt loading and dehydration as 

did the osmolal U/P ratio and the concentration s 

of both urinary and plasma electrolytes and urea. 

The most concentrated urine excreted by the 

camel was 3,200 mOsm kg-1 with urea 

contributing 900 – 1,400 mOsm L-1. The overall 

water expenditure of the camel was investigated 

in normally hydrated and dehydrated animals 

exposed to two ambient temperatures in a climatic 

chamber. The donkey in the same environment 

consumed and excreted more water and urine, 

respectively than the camel. The response of the 

camel to drinking NaCl solutions of various 

concentrations as it’s only source of drinking 

water was also investigated and it was concluded 

that the 1-humped camel could drink 3.5 - 5.5% 

NaCl solutions that were more concentrated than 

sea water. 

Maloiy, G. M. O. 1973a. The water metabolism of a 

small East African antelope: the dik-dik. Proceedings of 

the Royal Society of London 184:167-178. 

In controlled laboratory experiments, rectal 

temperature, cutaneous moisture evaporation, and 

respiratory rate were studied in the dik-dik 

(Rhynchotragus kirkii). The water balance of the 

dik-dik was investigated when the antelope were 

either fully hydrated or dehydrated at the 

environmental temperature of 22 oC or at 

temperatures alternating between 22 oC and 40 oC 

at 12 hr intervals. Fecal, urinary, and evaporative 

water losses were all reduced by varying degrees 

during dehydration at 22 oC and 22 to 40 - oC. The 

highest urine osmolality recorded was 4,318 ± 105 

mOsm kg-1 water that occurred when the 

antelopes were severely dehydrated. At air 

temperatures (40 to 45 oC) cutaneous evaporation 

measured with a non-ventilated sweat capsule was 

19 g water m2 –1 hr-1 and the respiratory rate over 

360 min-1. Thus the respiratory tract seems to be 

the major avenue for dissipating excess heat in 

dik-dik exposed to thermal stress. Injection of 

adrenaline, intravenously, stimulated sweat 

discharges similar to those observed in the small 

gazelles, sheep, and goats. The low-water 

exchange and an efficient kidney helps explain the 

ability of this small antelope to inhabit hot arid 

areas. 

Maloiy, G. M. O. 1973b. Water metabolism of East 

African ruminants in arid and semi-arid regions. Journal 

of Animal Breeding and Genetics 90:219-228. 

This paper reviews some aspects of the water 

metabolism of ruminants in East Africa, with 

special attention to the importance of water in 

limiting animal production and management in 

hot arid or semi-arid regions. Topics related to 

thermal and metabolic adaptations of some East 

African Bovidae to heat and aridity including 

water requirements, water turnover rates, effects 

of water restriction and heat loads on food intake, 

and water economy are reviewed in sheep, goats, 

camels, Thomson’s gazelle (Gazella thomsonii), 

impala (Aepyceros melampus), Grant’s gazelle 

(Gazella granti), Hartebeest (Alcelaphus 

buselaphus), oryx (Oryx besia), wildebeest 

(Connochaetes taurinus), waterbuck (Kobus 

defassa), buffalo (Syncerus caffer), eland 

(Taurotragus oryx), Zebu steer, and Hereford 

steer. 

Maloiy, G. M. O., B. M. Rugangazi, and E. T. Clemens. 

1988. Physiology of the dik-dik antelope. Comparative 

Biochemistry and Physiology 91A: 1-8. 

The overall life history and physiology of the dikdik antelope (Rhynchotragus kirkii) are reviewed. 

Aspects of the digestive physiology, physiological 

aspects of water metabolism, behavioral 

adaptations for thermoregulation, and 

reproduction are discussed. 
53 

Maloiy, G.M.O., B. M. Rugangazi, and E. T. Clemens. 

2000. Nitrogen metabolism and renal function in the 

dik-dik antelope (Rhynchotragus kirkii). Small Ruminant 

Research 37:243-248. 

Nitrogen metabolism and kidney function of the 

dik-dik antelope (Rhynchotragus kirkii) were 

studied under a range of controlled, experimental 

conditions and diets. Dik-dik antelope remained in 

nitrogen balance even when fed a diet low in 

protein and high in fiber. When fed a diet high in 

protein (20%) and water ad libitum, 55.3% of the 

urea altered by the kidney was reabsorbed. 

Limiting water intake increased urea reabsorption 

to 77.2%. The U/P urea concentrations were 

maintained at similar ratios on all diets, as well as 

during dehydration and solute loading. Minimum 

endogenous nitrogen excreted was 74 mg kg 0.75

day-1. Dehydration (water deprivation) and solute 

loading (intraruminal infusion of 0.25 M NaCl) 

had varying effects on nitrogen metabolism. It is 

concluded that the metabolic nitrogen economy of 

the dik-dik antelope is qualitatively similar to that 

of other domestic and wild ruminants. 

Maloiy, G. M. O. and C. D. H. Boarer. 1971. Response 

of the Somali donkey to dehydration: hematological 

changes. American Journal of Physiology 221:37-41. 

The effects of dehydration and rehydration on 

blood plasma osmolality, sodium, chloride, and 

hemoglobin concentration, packed cell volume 

(PCV), red blood cells (RBC), and plasma 

proteins in Somali donkeys and Zebu steer were 

studied under varying temperature regimes (22 – 

40 C) and under ad libitum and water restriction 

in the laboratory. Blood collection and titrated 

water methods were used. Increases in plasma 

osmolality, sodium, chloride, hemoglobin 

concentration, PCV, RBC, and plasma proteins 

were observed in dehydrated animals. Neither 

dehydration nor rehydration had any observable 

effect on mean cell hemoglobin, which remained 

at 22 pg (10-12 g) and 16 pg for the donkey and the 

Zebu steer, respectively, under all experimental 

conditions. In the donkey, decreases in mean cell 

volume and in intracellular and extracellular water 

were observed. Plasma volume was also reduced 

from a mean control value of 9.6 to 6.2 L. Most of 

the blood parameters were restored to their normal 

values within day after rehydration. 

Maloiy, G. M. O. and C. R. Taylor. 1971. Water 

requirements of African goats and haired-sheep. 

Journal of Agricultural Science 77:203-208. 

A number of species of desert-dwelling ungulates 

(e.g., Grant’s gazelle and oryx) can apparently 

survive desert conditions without drinking. We 

were interested in finding out whether goats and 

sheep herded in the arid Northern Frontier Region 

of Kenya utilized the same physiological 

strategies for reducing water requirements as the 

wild ungulates. Using simulated desert conditions 

(12 hr day-1 at 22 oC alternating with 12 hr day-1 at 

40 oC) in metabolic cages we found that both 

goats and sheep used water amounting to 8% of 

their body mass per day when water was available 

ad libitum; and this was reduced to about 4% of 

body mass when water intake was restricted. 

Evaporation was the major avenue of water loss 

under all experimental conditions. It was reduced 

from over 6% of body mass per day to about 3% 

in the simulated desert by restricting water intake. 

Restricting water intake had no effect on the 

temperature regulation of goats and sheep as had 

been observed in the wild desert-dwelling 

ungulates. It would appear that African goats and 

haired-sheep lack physiological mechanisms and 

are not free to utilize the behavioral mechanisms 

involved in freeing wild desert-dwelling ungulates 

for their dependence on drinking water. 

Maloiy, G. M. O., C. R. Taylor and E. T. Clemens. 1978. 

A comparison of gastrointestinal water content and 

osmolality in East African herbivores during hydration 

and dehydration. Journal of Agricultural Science 

91:249-254. 

Gastrointestinal water content and osmolality 

were determined in camel, sheep, goats, Zebu, 

Hereford cattle and donkeys during hydration and 

dehydration by removing the intestinal tract. The 

digesta water in the foregut was similar for all 

hydrated animals, whereas the water content of 

the distal colon showed more variation with 

animals that produce in the form of pellets had 

lower colon water content. During dehydration 
54 

only goats showed a reduction in foregut water 

content. During dehydration, donkeys were able to 

reduce the water content in the distal colon by 

10%, followed by camels with a reduction of 

6.8%, sheep, Zebu, and Hereford cattle exhibited 

reductions of 3 – 4%. Osmotic concentrations 

were higher in dehydrated animals than in 

hydrated animals. 

Maloiy, G. M. O. and D. Hopcraft. 1971. 

Thermoregulation and water relations of two East 

African antelopes: the hartebeest and impala. 

Comparative Biochemistry and Physiology 38A: 525-

534. 

In controlled laboratory experiments rectal 

temperature, cutaneous moisture evaporation and 

breathing rate were studied in the hartebeest 

(Alcelaphus buselaphus) and impala antelope 

(Aepyceros melampus). At the high air 

temperatures (40 - 50 oC), the sweating rate rose 

to 60 g water m2-1hr-1 and the respiratory rate to 

over 200 min-1 in both species. The water balance 

of the 2 species was investigated when the 

antelope were either fully hydrated or dehydrated 

at the environmental temperatures of 22 oC or 

alteration between 22 and 40 oC at 12-hr intervals. 

The total body water was estimated in 2 hartebeest 

antelope that were allowed to graze freely on the 

dry pastures of the Athi River Plains. 

Maloiy, G. M. O. and E. T. Clemens. 1980. Colonic 

absorption and secretion of electrolytes as seen in five 

species of East African herbivorous mammals. 

Comparative Biochemistry and Physiology 67A:21-25. 

Colonic absorption and secretion of electrolytes 

was studied in camels, zebu cattle, sheep, goats, 

and donkeys. The camel, sheep, goat, and donkey 

were equally efficient in recovering fluids from 

colonic contents, zebu cattle were least efficient. 

Compared to other species, Zebu cattle 

demonstrated a reduced sodium and water 

absorption, and net chloride secretion. Volatile 

fatty acid absorption was most evident in the 

colon of zebu cattle and the donkey. With the 

exception of the potassium flux, the camel, sheep, 

and goat demonstrated similar patterns of colonic 

electrolyte movement. 

Maloiy, G. M. O., R. N. B. Kay, and E. D. Goodall. 

1970. Digestion and nitrogen metabolism in sheep and 

red deer given large or small amounts of water and 

protein. British Journal of Nutrition 24:843-855. 

The interaction between nitrogen and water intake 

was studied in 2 female sheep and 2 red deer 

(Cervus elaphus). They were given pelleted diets, 

at maintenance level, containing equal amounts. 

Nearly three-quarters of the nitrogen of the highnitrogen rations but less than half of that of the 

low-nitrogen rations was excreted in the urine. 

Restriction of water intake reduced urinary 

nitrogen excretion by only about 1 g daily, mainly 

as a result of decreases in the excretion of urea 

and ammonia, but did not affect excretion of 

nitrogen in the feces. The urinary excretions of 

creatinine, creatine, hippuric acid, uric acid, and 

allantoin were also examined. The excretion of 

creatinine was not related to either nitrogen or 

water intake. The excretion of uric acid and of 

allantoin was greater in sheep than in the deer. 

The concentrations of urea in the plasma and of 

ammonia in the rumen fluid were measured before 

and after feeding. The plasma urea value was 

related to dietary nitrogen intake and was higher 

on the low-water than on the high-water regime. 

The rumen ammonia value also was related to the 

nitrogen intake but, while it generally increased 

after feeding when the high-nitrogen diet was 

given, it fell almost to zero 2 hr after feeding 

when the low-nitrogen diet was given. The sheep 

digested dry matter, cellulose, and nitrogen a little 

more fully than the deer. The high-water regime 

slightly increased the digestibility of dry matter 

and cellulose but did not affect the digestibility of 

nitrogen. 

Maloiy, G. M. O., W. V. Macfarlane, and A. Shkolnik. 

1979. Mammalian herbivores. Pages 185-209 in G. M. 

O Maloiy, editor. Comparative physiology of 

osmoregulation in animals. Volume 2. Academic Press, 

London, United Kingdom. 

This review covers osmoregulation in mammalian 

herbivores and includes discussion of diffusion, 

secretion, and cell osmoregulation. Water balance, 

electrolyte balance, milk and osmotic balance, and 

mineral deficiency are reviewed as they pertain to 
55 

maintenance of water balance by mammalian 

herbivores. 

Maltz, E. and A. Shkolnik. 1980. Milk production in the 

desert: lactation and water economy in the black 

Bedouin goat. Physiological Zoology 53:12-18. 

The black Bedouin goats that are herded in the 

extreme deserts of the Middle East are of small 

body size (16 - 26 kg). Even when lactating they 

drink only once every 2 days and can therefore 

graze far away from the widely spaced watering 

points. The water economy of the lactating 

Bedouin goats was studied under laboratory 

conditions (30 oC, 30% relative humidity). 

Maximum milk yield was 61 - 87 g kg-1 day-1; the 

volume of water consumed by lactating goats (158 

ml kg-1 day-1) was 3X the volume consumed 

before gestation. The rate of water turnover of the 

lactating goats (210 ml water kg-1 day-1) was 

double that as nonlactating females. The ability of 

the goats to withstand 2 days of water deprivation 

without the milk yield being affected is attributed 

to very high body water content, amounting to 77 

- 85% of the body mass. Following dehydration, 

when given free access to water, the goats at once 

replenish their entire water loss. Blood plasma 

volume was 9% of body mass in fully hydrated 

goats. During dehydration the blood plasma 

volume decreased in proportion to the decrease in 

total body fluids. Repeated periods of water 

deprivation had no effect on the ability to resume 

full milk production. 

Maltz, E., N. Silanikove, and A. Shkolnik. 1981. Renal 

performance in relation to water and nitrogen 

metabolism in Bedouin goats during lactation. 

Comparative Biochemistry and Physiology 70A:145-

147. 

Renal performance in relation to water and 

nitrogen metabolism in Bedouin goats during 

lactation were studied in the laboratory under 

conditions of 25 oC and 61% relative humidity. 

Water turnover rates were determined using 

titrated water and urea kinetics were assessed 

using 14C labeled urea. Black Bedouin goats at 4 – 

5 months post partum produce daily in the 

laboratory 50 g milk kg-1 body mass. Similar 

yields were recorded at mid-summer in goats 

herded in the desert where food is meager, low in 

protein and water is scarce. Urine concentration in 

lactating goats was higher than in goats before 

gestation but urine urea concentration was only a 

third that in non-lactating goats. The increase in 

urine volume in the lactating goats was less 

pronounced than the increase in drinking and 

water turnover rates or in food consumption. 

Daily renal absorption of urea in lactating goats 

amounted to 588 mmol compared to only 361 

mmol in non-lactating goats. Urea entry rate in 

lactating goats was 65% higher than in nonlactating goats, 748.6 mmol urea were recycled 

daily in lactating goats compared to only 227 

mmol in non-lactating goats. The role of the 

kidney plays in economizing both water and 

nitrogen metabolism in goats lactating in the 

desert is assessed and discussed. 

Maltz, E, K. Olsson, S. M. Glick, F. Fyhrquist, and N. 

Silanikove. 1984. Homeostatic responses to water 

deprivation or hemorrhage in lactating and non-lactating 

Bedouin goats. Comparative Biochemistry and 

Physiology, 77A:79-84. 

Three lactating and 3 non-lactating black Bedouin 

goats were subjected to 4 days of water 

deprivation or to hemorrhage, at the research zoo 

of Tel Aviv University. Four days of water 

deprivation caused body mass losses of 32 and 

23% and plasma volume losses of 30 and 34% in 

lactating and non-lactating goats, respectively. 

Plasma osmolality increased 17 and 15% in 

lactating and non-lactating goats. Plasma arginine 

vasopressin concentration rose from about 5 pg 

ml-1 to a mean of 36 pg ml-1. Plasma rennin 

activity increased from about 0.7 ng ml-1 hr-1 to a 

mean of 3.45 ng ml-1 hr-1 in lactating and to 3.15 

ng ml-1 hr-1 in non-lactating goats. At 4.5 hr postrehydration plasma osmolality and plasma 

vasopressin concentration were back to normal in 

non-lactating, but still elevated in lactating goats. 

Plasma rennin activity increased after rehydration. 

Rapid blood volume loss of 21 - 28% increased 

plasma vasopressin concentration to 16 - 35 pg/ml 

in non-lactating, but still elevated in lactating 

goats. Plasma rennin activity increased after 

rehydration. Rapid blood volume loss of 21 - 28% 

increased plasma vasopressin concentration to 16 
56 

- 35 pg ml-1 in non-lactating and to 70 or > 500 pg 

ml-1 in lactating goats. It is concluded that black 

Bedouin goats are well adapted to endure severe 

dehydration and rapid rehydration, but that they 

(especially lactating animals) react strongly to 

rapid volume depletion. 

Mitchell, D., S. K. Maloney, C. Jessen, H. P. Laburn, P. 

R. Kamerman, G. Mitchell, and A. Fuller. 2002. 

Adaptive heterothermy and selective brain cooling in 

arid-zone mammals. Comparative Biochemistry and 

Physiology 131B:571-85. 

Adaptive heterothermy and selective brain cooling 

are regarded as important thermal adaptations of 

large arid-zone mammals. Adaptive heterothermy, 

a process that reduces evaporation by storing body 

heat, ought to be enhanced by ambient heat load 

and by water deficit, but most mammals studied 

fail to show at least one of those attributes. 

Selective brain cooling, the reduction of brain 

temperature below arterial blood temperature, is 

most evident in artiodactyls, which possess a 

carotid rete, and traditionally has been considered 

to protect the brain during hyperthermia. The 

development of miniature ambulatory data loggers 

for recording body temperature allows the 

temperatures of free-living wild mammals to be 

measured in their natural habitats. All the African 

ungulates studied so far, in their natural habitats, 

do not exhibit adaptive heterothermy. They have 

low-amplitude nychthemeral rhythms of 

temperature, with mean body temperature over the 

night exceeding that over the day. Those with 

carotid retes (black wildebeest [Connocaetes 

taurinus], springbok [Antidorcas marsupialis], 

eland [Taurotragus oryx]) employ selective brain 

cooling but zebra, without a rete, do not. None of 

the rete ungulates, however, seems to employ 

selective brain cooling to prevent the brain 

overheating during exertional hyperthermia. 

Rather, they use it at rest, under moderate heat 

load, we believe in order to switch body heat loss 

from evaporative to non-evaporative routes. 

Mittal, S. B. 1980. Dairy development and seasonal 

variation in the quality of milk in the arid zone of 

western Rajasthan. Pages 381-387 in H. S. Mann, 

editor, Arid zone research and development. Scientific 

Publishers, Jodhpur, India. 

An investigation of the seasonal effect on the fat 

and non-fat solids contents of milk in western 

Rajasthan. It was found that the fat and non-fat 

solids contents tended to decline during summer 

and gradually increased through the monsoon 

season. The contents were maximum in the 

winter. It was concluded that the combined effect 

of environmental temperature, humidity, and feed 

seems to be the cause for the variation in the milk 

fat and non-fat solids contents. 

Mohammed A. and A. Al-hozab. 2004. Effect of water 

deprivation and season on feed intake, body weight and 

thermoregulation in Awassi and Najdi sheep breeds in 

Saudi Arabia. Journal of Arid Environments 59:71-84. 

Studies were conducted to compare responses to 

water deprivation in two local sheep breeds of 

Saudi Arabia, Awassi and Najdi, during different 

seasons. During water deprivation, body weight 

was significantly reduced by 11% during winter in 

both breeds, while it decreased 13.3% and 15.3% 

in Awassi and Najdi sheep in spring, and the 

corresponding values with reduction for summer 

were 18% and 21.5%. The decline in feed intake 

as a result of dehydration was highest in summer 

(96.5%) followed by spring (75%) and winter 

(62%) in both breeds. Water deprivation reduced 

respiration rate during winter and spring, and 

increased rectal temperature during spring and 

summer. Sweating rate was reduced in waterdeprived sheep during summer and Awassi breed 

maintained lower sweating activity. Both breeds 

were able to consume a volume of water within 15 

min following rehydration, which was amounting 

to 18.9%, 13.8% and 9.8% of their dehydrated 

body weights in summer, spring and winter, 

respectively. The lower rate of body weight loss 

and the maintenance of lower sweating activity 

during dehydration of Awassi indicated better 

ability of water conservation compared to Najdi 

breed. It was concluded that Awassi sheep possess 

better capability of withstanding water deprivation 

than Najdi sheep particularly when it was coupled 

with higher environmental temperature. 
57 

Mohamed, S. M., B. H. Ali and T. Hassan. 1988. Some 

effects of water deprivation on dorcas gazelle (Gazella 

dorcas) in the Sudan. Comparative Biochemistry and 

Physiology 90A:225-228. 

The effects of water deprivation on dorcas gazelle 

(Gazella dorcas) were studied in captive animals 

at the Khartoum Zoo, Sudan in May 1986. 

Animals were held in unshaded cages and the 

effects of dehydration for 10 days and subsequent 

rehydration for 2 days on some physiological and 

biochemical parameters were studied in the 

Dorcas gazelle. At the end of the 10 days of 

dehydration, feed intake and body mass were 

decreased by 42 and 29% of the control values, 

respectively. Rehydration restored most of the 

loss in feed intake and body mass. Dehydration 

decreased the water content in the feces of the 

gazelles by 41%. Rehydration restored 36% of the 

lost fecal water. Urine volume in dehydrated 

animals decreased by 66%, an effect that was 

readily reversed by rehydration. Blood 

hemoglobin of dehydrated gazelles decreased by 

22% but this effect was not reversed by 

rehydration for 2 days. Dehydration for 10 days 

decreased the concentration of serum glucose by 

34% and increased that of urea and albumin by 34 

and 18%, respectively. Rehydration for 2 days 

reversed these effects completely. The serum 

concentrations of sodium, potassium and chloride 

were increased by dehydration by 23, 44, and 18% 

respectively. After 2 days of rehydration the 

values returned to normal. No change in the heart 

rate, pulse or temperature was found during the 

dehydration period. The gazelles survived the 10 

days of dehydration, although they tended to be 

drowsy, weak and emaciated during the last 2 

days of dehydration. The animals appeared 

normal after rehydration. 

More, T. and K. L. Sahni. 1978. Effect of long term 

water deprivation on body weight and water intake of 

breeding ewes under semi-arid conditions. Journal of 

Agricultural Science 90:435-439. 

Thirty-nine adult female sheep of identical body 

size and age were randomly taken from the 

Chokla breed. They were divided into four 

groups, which were allowed water once in 24, 48, 

72, and 96 hr. Seven females from each of the 

first, third, and fourth groups were mated for the 

first time in spring and for a second time in 

winter, so that they lambed in the monsoon and 

summer season, respectively. All the females were 

maintained on uncultivated pasture. Watering 

once in 72 and 96 hr cause body mass loss up to 

26% compared with those watered daily. The 

females which failed to maintain pregnancy lost 

more than 30% of their body mass due to watering 

only once in 96 hr and there were about 43 and 

100% lambing in the first and second breeding 

cycle of the same females. The remaining groups 

displayed 100% lambing. The water intake 

increased significantly in the third month of 

pregnancy in the group allowed water daily and 

water consumption was found to be about 13% of 

body weight, whereas the values for those watered 

once in 72 and 96 hr were 9 and 8%, respectively. 

The water-deprived animals were able to drink up 

to 32% of their body mass within 2 – 3 min. It is 

concluded that breeding females could be watered 

once in 72 hr without any loss of lambing during 

summer. 

More, T. and K. L. Sahni. 1979. Effect of long-term 

intermittent watering on some blood and urine attributes 

of pregnant sheep under semi-arid conditions. Indian 

Journal of Animal Sciences 49:549-553. 

Blood and urine attributes were examined in 

breeding ewes maintained under different 

watering regimes of once in 24 (control), 72, and 

96 hr over a period of 1 year. Water deprivation 

significantly caused a progressive 

hemoconcentration and reduction in extracellular 

fluid space in all the groups of animals in both the 

stages of pregnancy during summer. An increase 

in extracellular fluid space on 130th day of 

pregnancy was significant and its level was higher 

in daily watered sheep during hot season than in 

winter. Watering intermittently increased plasma 

urea-nitrogen, non-esterified fatty acids, plasma 

bicarbonate and sodium, and changes were more 

pronounced during summer. Urinary osmolarity, 

specific gravity, and conductivity on 130th day of 

gestation showed increase with the water 

deprivation. There was also a reduction in urine 

K/Na ratio due to dehydration. It is concluded that 

breeding ewes could be given water once in 72 
58 

hours during summer without any serious clinical 

changes in the blood and urine. 

More, T. and K. L. Sahni. 1980. Effect of water 

deprivation on blood and urine components of lactating 

sheep under semi-arid conditions. Indian Journal of 

Animal Science 50:411-416. 

Effect of water deprivation was studied in 21 

Chokla sheep using blood and urine samples. 

Sheep were provided with water ad libitum once 

in 24, 72, and 96 hr (group 1, 2, and 3, 

respectively). First and second lambing in these 

animals took place in July and May, respectively. 

Animals were sampled on the 30th and 60th days 

post-lambing for blood analysis. Extracellular 

fluid values were maintained on low levels in 

group 3 on 30th and 60th days after first lambing. It 

declined significantly on the 60th day of lactation 

in all groups. There was a higher level of 

extracellular space in group 2 during the second 

breeding cycle. Plasma-free fatty acids and urea 

nitrogen increased significantly with dehydration. 

However, there was no evidence of 

hemoconcentration either in hemocrit or 

hemoglobin levels, which were lower in all the 

females on the 30th day of lactation than the 60th

day. Data on plasma sodium, potassium, and 

bicarbonate inconsistently responded during 

watering treatment. The deprivation of water 

caused significant increases in urine osmolarity 

and conductivity. There was also a rise in urine 

sodium concentration and thereby reduction in the 

potassium/sodium ratio. The present study showed 

lactating Chokla females were able to tolerate 

dehydration for 3 to 4 days during the rains and 

mid-summer of semi-arid area. 

Morris, R. J. H., B. Howard, and W. V. Macfarlane. 

1962. Interaction of nutrition and air temperature with 

water metabolism of merino wethers shorn in winter. 

Australian Journal of Agricultural Research 13:330-334. 

Field observations were made on Peppin merino 

wethers at 6 and 9 per 0.4 ha throughout the year 

on improved pasture in Canberra, Australia. 

Estimations of water distribution with the use of 

tritium, thiocyanate, and T1824 indicated that 

stocking rate in autumn had little effect on body 

composition or water intake. Before shearing in 

July, however, the 9-per-0.4 ha sheep had lost 

16% more weight than those at 6-per-0.4 ha, 

although body water distribution was similar in 

the two groups. After shearing, both groups 

shivered continuously for three weeks. The 6-per0.4 ha animals had lower rectal and higher skin 

temperatures than the 9-per-0.4 ha sheep. Skin 

and rectal temperatures were reciprocal to wind 

velocity. Both groups lost over 3 kg weight (5.9 

and 8.4% of body mass) in 2 weeks, but in the 9-

per-acre sheep, body water increased by 8.7% 

while in the 6-per-0.4 ha group 4.4% of body 

water was lost. The 9-per-0.4 ha sheep lost 30.7% 

of tissue solids, compared with 7.5% in the betterfed animals. It is likely that cellular water content 

increased in the 9-per-0.4 ha animals. An increase 

in density of stocking from 6 to 9-per-0.4 ha costs 

three times as much tissue and fat during the cold 

period, while this loss of solids was partly 

obscured by replacement of tissues with water. 

Murray, D. M. 1966. A comparison of cutaneous 

evaporation rates in cattle exposed to heat in a climate 

laboratory and in the field. Journal of Agricultural 

Science 66:175-179. 

The cutaneous evaporation rates of 3 animals of 

different genotype have been determined under 

artificial heating in the laboratory and during 

exposure to field conditions. Cutaneous 

evaporation rates were measured from the backthoracic region using a ventilated capsule 

technique. In both climate-laboratory studies and 

field observations cutaneous evaporation showed 

little relationship with rectal temperature, 

respiratory rate, or skin temperature. Basal 

cutaneous evaporation rates in the unheated 

chamber at 10 a.m. were found to be 40% lower in 

animals which were housed overnight than in 

those which entered the chamber following 

exposure to early morning sunlight. Only minor 

differences in cutaneous evaporation rates of the 3 

animals were observed during either hot-room or 

field studies, despite their variation in genotype 

and sweat gland density. Under field conditions, 

cutaneous evaporation rates were almost twice 

those obtained during climate-controlled 

laboratory exposures, although the animals had 

lower rectal temperatures, respiratory rates, and 
59 

skin temperatures throughout the field 

observations. Changes in moisture loss from the 

skin in animals exposed to field conditions closely 

followed fluctuations in direct solar radiation. It is 

suggested than the sweat glands of cattle may be 

stimulated to a greater extent by direct solar 

radiation in the field than by artificial heat such as 

that encountered during climate-laboratory 

exposures. 

Musewe, V. O., G. M. O. Maloiy, and J. K. Kanja. 1976. 

Evaporative water loss in two small African antelopes: 

the dik-dik and the suni. Comparative Biochemistry and 

Physiology 53C:17-18. 

In a temperature controlled chamber in the 

laboratory at the University of Nairobi, Kenya, 

Africa, experiments on the pulmocutaneous water 

loss, respiratory rate, rectal and skin temperatures 

of the dik-dik (Rhynchotragus kirkii) and the suni 

(Nesotragus moschatus) were measured before 

and during exposure to heat stress. Body 

temperature was assessed using thermocouples 

and cutaneous evaporation was determined by 

placing a desiccant capsule on a shaved area of 

skin. During exposure to thermal stress (Ta > 40 

oC) increases were noted in all measured 

parameters except sweating rate in both species. 

In both dik-dik and the suni antelopes, sweating 

did not appear to be an important avenue of 

evaporative heat loss during heat exposure. 

Intradermal injections of adrenaline and 

noradrenaline stimulated sweating while 

injections of acetylcholine, carbachol, prolactin, 

oxytocin and isoprenaline had negligible effects 

on sweating. 

Nagy, K. A and M. H. Knight. 1994. Energy, water, and 

food use by springbok antelope (Antidorcas 

marsupialis) in the Kalahari Desert. Journal of 

Mammalogy 75:860-872. 

Field-metabolic rates and water-influx rates (both 

measured via doubly-labeled water) and diet 

composition (rumen contents, plant sample 

analyses) were measured in free-ranging male 

springbok antelope (Antidorcas marsupialis) 

during 3 seasons in 1986 and 1987 at Kalahari 

Gemsbok National Park, South Africa and 

Gemsbok National Park, Botswana. Results from 

springbok that did not drink water during the hot, 

dry season indicate that they can achieve water 

balance without drinking if they can obtain plant 

food containing at least 67% water. Springbok 

may accomplish this by selecting flowers, seeds, 

and leaves of shrubs (mainly Acacia mellifera and 

A. hebeciada) before dawn, when these foods are 

most succulent. Springbok ate mostly grass during 

the hot seasons if drinking water was available, 

but, in the cold, dry season, their selection of 

succulent shrub leaves mainly (A. mellifera) 

apparently made them independent of drinking 

water. During the rut, males had high energy and 

water requirements and lost weight because they 

did not eat enough food to maintain balance. 

During most of the year, springbok used water 

and energy at comparatively low rates, in common 

with other desert adapted mammals. Their watereconomy index was also low, indicating a 

conservative water metabolism. We estimated that 

an adult male springbok consumes ca. 504 kg (dry 

matter) of food year-1 and that the population of 

springbok consumed ca 76% of the annual grass 

productivity within the important dry riverbed 

habitats. Competition with other large grazers, and 

particularly with those restricted to foraging in 

close proximity to drinking water, probably 

existed during dry years of this study. 

Nicholson, M. J. 1987. The effect of drinking frequency 

on some aspects of the productivity of zebu cattle. 

Journal of Agricultural Science 108:119-128. 

A 28-month trial was carried out under extensive 

grazing conditions to examine the effects of 

giving water to Boran cattle once daily, once 

every 2 days, and once every 3 days, with cattle 

having ad libitum access to water serving as the 

control. In the dry season, the mass and condition 

of lactating cows given water every 3 days 

declined more rapidly than that of cows given 

water daily. Calving rates and birth weights were 

unaffected by treatments although when compared 

with cows given water ad libitum, birth weights 

were depressed by 2.5 kg in all treatments. Thirty 

steers showed no treatment differences in 28-

month weights despite a depression in dry matter 

intake in the dry season by animals given water 

every 3 days. In contrast, 210-day weaning 
60 

weights were significantly depressed by 9 kg 

when cattle drank water every 2 days and 14 kg 

when they drank every 3 days compared with 

calves given water daily. Total water consumed 

was depressed in all classes of stock by 5 – 10% 

under the 2-day regime and by 25 – 34% under 

the 3-day regime when compared to cattle given 

water daily. The results show that giving water 

every 3 days can be carried out indefinitely with 

all classes of stock with only minor effects on 

cattle productivity under the climatic conditions in 

which the trial was held. The management 

implications of giving water every 2 to 3 days to 

cattle under extensive, pastoralist and ranching 

conditions are discussed. 

Nolan, J. V., J. B. Liang, N. Abdullah, H. Kudo, H. 

Ismail, Y. W. Ho and S. Jalaludin. 1995. Food intake, 

nutrient utilization and water turnover in the lesser 

mouse-deer (Tragulus javanicus) given lundai (Sapium 

baccatum). Comparative Biochemistry and Physiology 

111A:177-182. 

Voluntary food intake, digestibility and water 

turnover were determined in adult Malaysian 

lesser mouse-deer (Tragulus javinicus) given 

unlimited access to lundai foliage (Sapium 

baccatum). Daily dry matter (DM) intake was 

42.4 g kg-1 metabolic live mass (M0.73) or 3.7% M. 

Digestible energy intake was 853 kJ day-1 (571 kJ 

metabolizable energy M0.73), calculated to be used 

with 79% efficiency. Apparent digestibility (%) of 

organic matter was 83.8, crude fiber 63.7, acid 

detergent fiber 60.5, neutral detergent fiber 72.1 

and crude protein 65.0. Urinary excretion of the 

purine derivative, allantoin, was 0.05 mg g-1

digestible DM intake suggesting rumen microbial 

yield efficiency may be lower than in other 

ruminant species. Total water intake was 182 ml 

M0.82, consistent with a very lean carcass. 

Turnover of body water was 17% day-1. The 

mouse-deer produced relatively dry, well-defined 

fecal pellets. 

Olsson, K., S. Benlamlih, K. Dahlborn, and F. Fyhrquist. 

1982. Effects of water deprivation and hyperhydration in 

pregnant and lactating goats. Acta Physiologica 

Scandinavica 115:361-367. 

The response to 30 hr water deprivation was 

studied in 7 goats during the last month of 

pregnancy and during lactation with anestrus as 

the control period. Plasma osmolality and plasma 

Na concentration increased by about 4% in 

pregnant and lactating goats and by about 2% in 

anestral goats. Plasma arginine vassopressin 

concentration rose by about 7 pg ml-1 in pregnant 

and lactating goats, but by about 3 pg ml-1 during 

anestrus. Plasma rennin activity was elevated in 

pregnant animals, but dehydration caused only a 

minor further rise. Total plasma protein 

concentration was low in pregnant goats and did 

not increased during water deprivation, but it did 

so in lactating animals, but remained unchanged 

during anestrus. Effective renal plasma flow fell 

by 20% in lactating animals, but no consistent 

effect of the dehydration was seen during 

pregnancy and anestrus. Urine flow decreased by 

about 75% during pregnancy, 55% during 

lactation and 65% during anestrus with the highest 

urine osmolality observed during anestrus. Milk 

production was only slightly reduced, but the milk 

osmolality increased in parallel with that of the 

blood plasma. When allowed to drink at the end of 

the water deprivation period, pregnant goats 

immediately drank 2.5 ± 0.5 L, lactating goats 3.3 

± 0.9 L and anestral goats 1.1 ± 0.3 L. When 

hyperhydrated, pregnant goats excreted the 

excessive water more readily and showed less 

response to exogenous AVP than lactating and 

anestral animals. In conclusion, pregnant and 

lactating goats are obviously more susceptible to a 

shortage of water supply than anestral animals but 

can easily excrete an excess of water. 

Osman, H. E. and B. Fadlalla. 1974. The effect of level 

of water intake on some aspects of digestion and 

nitrogen metabolism of the desert sheep of the Sudan. 

Journal of Agricultural Science 82:61-69. 

Five successive trials were conducted using 8 

adult rams (Sudan desert sheep) to study the effect 

of restriction of water intake on some aspects of 

digestion and nitrogen metabolism. The feeds 

used in this study were berseem hay (Medicago 

sativa), lubia hay (Dolichos lablab), maize hay 

(Zea mais), a concentrate mixture, and dry desert 

grasses (hummra---a mixture of Dactyloctenium 

aegyptium, Schoenefeldia gracilis, Eragrostis 
61 

pilosa, Aristida funiculate, and Aristida spp.). 

Restriction of water did not affect the digestibility 

coefficients of organic matter, crude protein, and 

crude fiber significantly. The digestibility 

coefficient of ether extract was significantly 

reduced whereas that of nitrogen-free extract was 

slightly higher when water was restricted. The 

concentrations of ammonia and volatile fatty acids 

in the rumen and of urea in the blood were 

recorded before and 3 hr after feeding. Increases 

in the rumen ammonia and blood urea nitrogen 

concentration were reduced by water restriction 

except when hummra was fed. Restriction of 

water intake also slightly increased the in vitro

rate of fermentation of rumen contents which is 

taken as a measure of microbial activity in the 

rumen, and the retention of nitrogen. These results 

are interpreted as indications of more efficient 

nitrogen utilization under conditions of water 

restriction. There were no significant effects of the 

treatments on changes in the concentration of 

volatile fatty acids. The significance of these 

findings in relation to the management of desert 

sheep in arid parts of Sudan is discussed with 

special reference to the effect of the level of drymatter intake on nitrogen balance. 

Parker, K. L. 1988. Effects of heat, cold, and rain on 

coastal black-tailed deer. Canadian Journal of Zoology 

66: 2475-2483. 

Effects of heat, cold, and rain on costal blacktailed deer (Odocoileus hemionus columbianus) 

we recorded in a metabolic chamber at dry air 

temperatures between –20 and 32 oC. For animals 

in summer pelage, respiratory rates, body core 

temperatures, and skin temperatures increased 

curvilinearly with increasing air temperature; 

thermally critical air temperatures occurred above 

27 oC and below 10 oC. In winter body 

temperatures were lower in adults than in fawns, 

skin temperatures were highly variable, and 

respiratory rates increased at lower air 

temperatures than in summer; metabolic 

expenditures associated with thermoregulation 

increased at temperatures above freezing. During 

summer trials in the rain, body and skin 

temperatures at air temperatures greater than 12 

oC; at 10 oC, energy expenditures after 5 hr of 

rainfall were greater than during heat or cold 

stress. For animals in winter pelage, changes in 

body temperature, skin temperature, and hair 

depth showed no consistent trends with duration 

of rainfall; only fawns increased metabolism at 

temperatures just above freezing (2 – 3 oC) in the 

rain. Data from this study suggest that rainfall 

may pose major energetic constraints for blacktailed deer in summer pelage. Managerial 

provisions for thermal cover should place highest 

emphasis on summer habitats. 

Parker, K. L. and C. T. Robbins. 1984. 

Thermoregulation in mule deer and elk. Canadian 

Journal of Zoology 62: 1409-1422. 

Thermoregulatory responses of mule deer 

(Odocoileus hemionus hemionus) and elk (Cervus 

elaphus nelsoni) were analyzed for air 

temperatures outdoors between 2 and 34 oC in 

summer and -38 and +24 oC in winter. Body 

temperatures differed between species, seasons, 

and ages. Surface skin temperatures varied with 

air temperature, incident radiation, and seasonal 

pelage. Respiratory rate and water loss increased 

exponentially while exhaled air temperatures 

varied sigmoidally as air temperature increased. 

Expired air volume increased logarithmically with 

increasing respiratory rate. Cutaneous evaporation 

(g m-1 hr-1) in summer was significantly greater in 

elk than in mule deer, which used panting as the 

primary means of heat dissipation in hot 

environments. Nonevaporative respiratory heat 

loss varied parabolically as a function of air 

temperature in both species. Thermally critical 

environments for mule deer occurred at operative 

temperatures of less than -20 oC and greater than 5 

oC in winter and greater than 25 oC in summer. 

Energy expenditures increased for elk at operative 

temperatures below -20 oC and above +20 oC in 

winter, with metabolic rates decreasing between 

10 and -20 oC. Maximum thermal resistances for 

mule deer and elk in winter were 1,400 and 2,000 

s m-1, respectively, compared with 600 and 400 s 

m-1 in summer. 

Parker, K. L., M. P. Gillingham, T.A. Hanley and C. T. 

Robbins. 1993. Seasonal patterns in body mass, body 

composition, and water transfer rates of free-ranging 
62 

and captive black-tailed deer. Canadian Journal of 

Zoology 71:1397-1404. 

Body mass, body composition, and water turnover 

rates were determined over a continuous 2-year 

period in 9 free-ranging Sitka black-tailed deer 

(Odocoileus hemionus sitkensis) on Channel 

Island, Wrangell, Alaska and 8 captive deer 

between 1988 and 1990 using titrated water. Body 

masses showed a cyclic pattern, declined 14 - 

31% between October and March, and were best 

described by a 5-parameter, biologically based 

regression model. The amount of mass lost by 

black-tailed deer over winter depended on the 

peak body mass attained during fall. During 

winter, animals used 70-82% of their body fat and 

10 - 15% of protein reserves. Body fat was 

preferentially mobilized at rates 2.3 - 11.6 times 

higher than protein. Because of the higher energy 

content of fat, fat accounted for 83 – 92% of the 

catabolized energy. Water transfer rates varied 

seasonally with average summer values 

approximately four times those of winter; 

lactating deer had significantly higher rates of 

water transfer than nonlactating animals. Seasonal 

changes in all of the above parameters for wild 

deer were greater than those for eight deer of the 

same age in captivity 

Rosenmann, M. and P. Morrison. 1963. Physiological 

response to heat and dehydration in the guanaco. 

Physiological Zoology 36:45-51. 

The response to heat and dehydration was studied 

in the guanaco (Lama guanicoe) using captive 

animals (1 M and 1 F) in a climate-controlled 

room at the Santiago Zoo, Santiago, Chile. The 

guanaco regulated its body temperature with little 

variation at ambient temperatures up to 45 oC for 

6 hr at 15% relative humidity and following 

severe dehydration for 24 hr. The resting heart 

rate did not change from the normal range during 

heat stress even in the severely dehydrated animal. 

Hemoconcentration, determined via blood 

extractions, occurred following dehydration in 

proportion to the weight change of the body as a 

whole. The normal guanaco did not increase its 

respiratory rate, however, the dehydrated animal 

showed substantial hypernoea. 

Rubsamen, K., R. Heller, H. Lawrenz, and W.V. 

Engelhardt. 1979. Water and energy metabolism in the 

rock hyrax (Procavia habessinica). Journal of 

Comparative Physiology 131B:303-309. 

The influence of ambient temperature and water 

supply on water metabolism and O2-consumption 

was measured in rock hyraxes (Procavia 

habessinica) in the laboratory using titrated water. 

With ad libitum food and water (control), water 

turnover rates of hyraxes were significantly lower 

than the general eutherian mean; water turnover 

rates were 61.4, 44.1, and 55.1 ml kg-0.82 day-1 at 

20, 27, and 35 oC, respectively. When greens were 

fed ad libitum and no drinking water was given, 

water turnover rate at 20 oC was two-fold higher, 

but at 27 and 35 oC was similar to that in control 

experiments. Water turnover rates were 

significantly reduced when no drinking water and 

only 25 g greens/day were offered (25.8, 22.0, and 

29.3 ml kg-0.82 day-1 at 20, 27, and 35 oC, 

respectively). Highest urine osmolality (3,200 

mOsm kg-1) was recorded at 35 oC. Oxygen 

consumption under control conditions was 43% 

below that predicted on the basis of body mass for 

most eutherian mammals. The thermoneutral zone 

ranged from 27 to 35 oC, and the basal metabolic 

rate was 165 kJ kg-0.75 hr-1. 

Rubsamen, K. and S. Kettembeil. 1980. Effect of water 

restriction on oxygen uptake, evaporative water loss 

and body temperature of the rock hyrax. Journal of 

Comparative Physiology 138B:315-320. 

Evaporative water loss, O2 consumption and body 

temperature were measured using titrated water in 

3 rock hyraxes (Procavia habessinica) under 

control and restricted water intake conditions, in 

the laboratory in Stuttgart, Germany. Water 

turnover rate was 61 ± 6 ml kg-0.82 day-1 during 

control experiments and 37 ± 6 ml kg-0.82 day-1

during water restriction. Water restriction reduced 

O2 consumption below ambient temperatures (Ta) 

of 28 and above 33 oC; there was no effect within 

the thermoneutral zone. Between 12 and 27 oC 

total evaporative heat loss decreased from 0.41 ± 

0.05 W kg-1 during control experiments during 

control experiments to 0.34 ± 0.04 W kg-1 during 

water restriction. Between 39 and 41 oC 

evaporative heat loss increased to 1.61 W kg-1

during ad libitum and 0.72 W kg-1 during 
63 

restricted water availability. During control 

experiments body temperature ranged between 37 

and 40 oC as Ta was changed between 12 and 38 

oC. During water restriction the animals became 

hypothermic below and hyperthermic above a Ta

of 27 oC. 

Rubsamen, K. and W. V. Engelhardt. 1975. Water 

metabolism in the llama. Comparative Biochemistry and 

Physiology 52A:595-598. 

Water metabolism of llamas (Llama llamae) and 

goats under conditions of ad libitum feeding 

(control) and under restricted food and water 

intake was measured using titrated water, in 

Stuttgart, Germany. Water turnover rates at 

control feeding were 62.1 ± 8.8 ml kg-0.82 day-1 in 

llamas and 59.0 ± 10.9 ml kg-0.82 day-1 in goats. 

Values decreased with reduced food intake to 46.9 

± 7.3 ml kg-0.82 day-1 and 41.1 ± 8.0 ml kg-0.82 day1

. Under condition of reduced water intake, goats 

reduced food intake more than llamas. 

Rubenstein, D. I. 1989. Life history and social 

organization in arid adapted ungulates. Journal of Arid 

Environments 17:145-156. 

The life history and social organization of 

ungulate species adapted to arid environments is 

reviewed. The review includes coverage of the 

theories of life history, mating system evolution, 

and ecological features of arid environments. The 

author then makes broad and detailed interspecific 

and intraspecific comparisons of life history and 

social organization of ungulates inhabiting arid 

environments. 

Rungangazi, B. M. and G. M. O. Maloiy. 1987. Salt 

excretion and saline drinking in the dik-dik antelope 

(Rhynchotragus kirkii). Comparative Biochemistry and 

Physiology 88A:331-336. 

The ability of the dik-dik antelope 

(Rhynchotragus kirkii) to survive while drinking 

saline solutions was tested in controlled laboratory 

experiments by providing drinking water 

containing up to 0.5 M NaCl. Fluid intake 

increased from 230.5 ml day-1 when fresh water 

was offered to a maximum of 373.9 ml day-1 when 

0.3 M NaCl solution was offered. At 

concentrations higher than 0.3 M animals lost 

weight, were anorexic, and developed diarrhea. It 

is concluded that the dik-dik antelope will 

probably tolerate drinking water containing 0.24 

M NaCl. 

Russel, A. J. F., J. Z. Foot, and D.M. McFarlane. 1982. 

Use of titrated water for estimating body composition in 

grazing females. Pages 45-56 in Use of titrated water in 

studies of production and adaptations in ruminants. 

International Atomic Energy Agency, Vienna, Austria. 

Titrated water was used to estimate total body 

water, body composition, and water turnover of 

non-pregnant, pregnant, non-lactating, and 

lactating grazing sheep. Body composition was 

estimated from equilibrated and extrapolated 

values of titrated water space. These methods both 

overestimated the total body water measured 

directly. Body fat could be predicted satisfactorily 

from titrated water space within the physiological 

states of females (i.e., lactating, pregnant), 

although for lactating females the error of 

prediction is greater. It appears inadvisable at this 

stage to use equations derived from all classes of 

females to estimate body fat in females of any 1 

physiological state. Water turnover varied, with 

the physiological state being highest for lactating 

females. 

Schmidt-Nielsen, K. 1959. The physiology of the camel. 

Scientific American 200:140-151. 

Reviews the overall physiology of the camel in 

relation to thermoregulation and water balance, 

particular adaptations that allow the camel to 

tolerate dehydration in a hot arid environment. 

Physiological mechanisms discussed include total 

body water, routes of water loss, nitrogen 

metabolism, and adaptive heterothermy. 

Schmidt-Nielsen, K., B. Schmidt-Nielsen, S. Jarnum, 

and T. R. Houpt. 1956. Water balance of the camel. 

American Journal of Physiology 185:185-194. 
64 

Camels were exposed to prolonged periods of 

water deprivation during winter, spring, and 

summer under laboratory conditions in the Sahara 

Desert. Determinations were made of weight 

changes, water and food intake, urine flow and 

concentrations, and plasma concentrations. It was 

found that the camel can tolerate a loss of water 

corresponding to 30% of its body mass even when 

exposed to the severe desert heat. Other mammals 

dehydrated in a hot environment may die from 

circulatory failure when the water loss involves 

12% of the body mass. Unlike many other 

mammals the camel des not lose its appetite when 

deprived of water but continues to eat normally 

until the desiccation becomes very severe. It has 

low urine output (0.5 – 1 L day-1 when kept on a 

diet of dates and hay), a low water content in the, 

and, when dehydrated in the summer, a very low 

evaporative water loss. When offered water the 

camel drinks in 10 minutes enough water for 

complete rehydration. The longest period that a 

camel was kept on dry food without drinking 

water in the hot summer was 17 days. This camel 

was not working and it had its protective fur, 

which decreased the heat gain from the 

environment. It is concluded that the ability of the 

camel to withstand prolonged dehydration is due 

to a tolerance to an extremely high degree of 

desiccation of the body and low overall water 

expenditure. Particularly effective as a water 

conserving mechanism is the low evaporative 

water loss during dehydration in the summer. 

Schmidt-Nielsen, K. and B. Schmidt-Nielsen, S. Jarnum 

and T. R. Houpt. 1957. Body temperature of the camel 

and its relation to water economy. American Journal of 

Physiology 188: 103-112. 

Body temperature of the camel and its relation to 

water economy were studied at Beni Abbes, 

Algeria. The rectal temperatures of normal 

healthy camels at rest may vary from about 34 oC 

to more than 40 oC. Diurnal variations in the 

winter are usually in the order of 2 oC. In summer 

the diurnal variations in the camel deprived of 

drinking water may exceed 6 oC, but in animals 

with free access to water the variations are similar 

to those found in the winter. The variations in 

temperature are of great significance in water 

conservation in 2 ways. The increase in body 

temperature means that heat is stored in the body 

instead of being dissipated by evaporation of 

water. The high body temperature means that heat 

gain from the hot environment is reduced because 

the temperature gradient is reduced. The effect of 

the increased body temperature on heat gain from 

the environment has been calculated from data on 

water expenditure. These calculations show that 

under the given conditions the variations in body 

temperature effect considerable economy of water 

expenditure. The evaporative heat regulation in 

the camel seems to rest exclusively on 

evaporation from the skin surface (sweating), and 

there is no apparent increase in respiratory rate or 

panting connected with heat regulation. The 

evaporation from isolated skin areas increased 

linearly with increased heat load. The critical 

temperature at which the increase sets in is around 

35 oC. The fur of the camel is an efficient barrier 

against the heat gain from the environment. 

Schmidt-Nielsen, K. and B. Schmidt-Nielsen, T.R. 

Houpt, and S. Jarnum. 1956. The question of water 

storage in the stomach of the camel. Mammalia 20:1-

15. 

The paper discusses evidence that the camel stores 

water in its stomach. The evidence presented does 

not support the water storage hypothesis. The 

water storage function is generally ascribed to a 

special sac-like structures in the camel’s rumen. 

The contents of these sacs usually is more solid 

than the general rumen contents. The sacs have a 

glandular structure. The fluid present is similar to 

digestive fluids, particularly saliva. It has no 

particular resemblance to drinking water, neither 

in appearance nor in chemical composition. The 

camel usually drinks an amount of water 

sufficient to restore the water content of the body. 

In these experiments, water was not ingested in 

excess of that needed to restore the normal 

composition of the body. After large amounts of 

water had been ingested the fluid in the rumen 

attained its usual composition in about 2 days. 

The rumen of the camel, like that of other 

ruminants, contains a large amount of fluid. 

Schmidt-Nielsen, K., E. C. Crawford, A. E. Newsome, 

K. S. Rawson, and H. T. Hammel. 1967. Metabolic rate 
65 

of camels: effect of body temperature and dehydration. 

American Journal of Physiology 212:341-346. 

The effect of body temperature and hydration 

state on metabolic rate were studied in captive 

camels in Alice Springs, Australia. The metabolic 

rate increased with increasing body temperature as 

expressed by a mean Q10 of 2.06. The metabolic 

rate decreased with increasing dehydration, 

reaching about 77% of the original value at 77% 

of the initial hydrated body rate. The rate of 

respiration increased with rising body temperature 

with a mean Q10 of 10.86. The rate of respiration 

was decreased to 64% of the initial value when 

dehydration had reduced the body mass to 77% of 

the initial weight. 

Schmidt-Nielsen, K., E. C. Crawford, and H. T. 

Hammel. 1981a. Respiratory water loss in camels. 

Proceedings of the Royal Society of London B 211:291-

303. 

Rates of oxygen consumption and respiratory 

water loss were studied in captive camels that 

were exposed to desert heat and water deprivation 

at Alice Springs, Australia. Body temperatures 

were measured using thermocouples and oxygen 

consumption was determined using a facemask. 

We found that changes in body temperature are 

accompanied by considerable changes in 

respiratory water loss. Body temperature 

fluctuations are greatest in dehydrated camels (up 

to 70 oC), and in these the respiratory water loss 

might vary from about 0.06 to 1.2 g min-1. The 

respiratory frequency varied from about 4 to 28 

min-1, while the metabolic rate varied by less than 

two-fold. The lowest values for respiratory water 

loss can be explained by the exhalation of air at 

temperatures far below body temperature, and, in 

addition, removal of water vapor for the exhaled 

air, resulting in exhalation of air at less than 100% 

relative humidity. 

Schmidt-Nielsen, K., R. C. Schroter, A. Shkolnik. 

1981b. Desaturation of exhaled air in camels. 

Proceedings of the Royal Society London. B 211:305-

319. 

We have found that camels can reduce the water 

loss due to evaporation from the respiratory tract 

by decreasing the temperature of the exhaled air 

and by removal of water vapor from this air, 

resulting in the exhalation of air at less than 100% 

relative humidity. Camels were kept under desert 

conditions and deprived of drinking water. In the 

daytime the exhaled air was at or near body core 

temperature, while in the cooler night exhaled air 

was at or near ambient air temperature. In the 

daytime the exhaled air was fully saturated, but at 

night its humidity might fall to approximately 

75% relative humidity. The combination of 

cooling and desaturation can provide a saving of 

water of 60% relative to exhalation of saturated 

air at body temperature. The mechanism 

responsible for cooling of the exhaled air is a 

simple heat exchange between the respiratory air 

and surfaces of the nasal passageways. On 

inhalation these surfaces are cooled by the air 

passing over them, and on exhalation heat from 

the exhaled air is given off to these cooler 

surfaces. The mechanism responsible for 

desaturation of the air appears to depend on the 

hygroscopic properties of the nasal surfaces when 

the camel is dehydrated. The surfaces give off 

water vapor during inhalation and take up water 

from the respiratory air during exhalation. We 

have used a simple mechanical model to 

demonstrate the effectiveness of this mechanism. 

Schoen, A. 1968. Studies on the water balance of the 

East African goat. East African Agriculture and Forestry 

Journal 34:256-262. 

The water balance of East African goats has been 

determined under normal conditions and under 

heat stress and water restriction. Water balance 

was calculated using the measurements of the 

amount of water drank, water content of food, 

water lost in feces and urine, and estimates of 

metabolic water. Water loss through urine, feces, 

and cutaneous evaporation decreased in goats 

under water restriction. Goats under water 

restriction increased urine osmolarity and allowed 

small increases in body temperature. Goats also 

maintained high food intake rates during water 

restriction. 
66 

Schoen, A. 1969. Water conservation and the structure 

of the kidneys in tropical bovids. Journal of Physiology 

204:143-144. 

Water balance and the response to dehydration in 

relation to kidney structure was studied in the 

bushbuck (Tragelaphus scriptus) from moist 

bushland, the Uganda kob (Adenota kob) from dry 

savannah, and the dik-dik (Rhyncotragus kirkii) 

from semi-desert habitats. It was found that when 

animals were dehydrated to 85% of normal body 

mass, the urine output fell from 99.1 ± 8.4 to 69.7 

± 2.0 ml kg0.73 day-1 in the bushbuck, from 46.4 ± 

3.7 to 27.2 ± 1.5 ml kg0.73 day-1 in the kob, and 

from 10.9 ± 0.77 to 1.3 ± 0.04 ml kg0.73 day-1 in 

the dik-dik. Urine osmolalities rose from 936 ± 52 

to 1,369 ± 52 mOsm L-1 in the bushbuck, from 

1,109 ± 16 to 1,594 ± 11 mOsm L-1 in the kob, 

and from 2,235 ± 138 to 4,762 ± 62 mOsm L-1 in 

the dik-dik. Kidney measurements from 6 

individuals from each species showed that the 

medullae occupied a mean of 31% in the 

bushbuck, 38% in the kob, and 47% in the dikdik; these differences were significant. If the 

relative medullary volume is a measure of the 

total length of the loop of Henlé, it may then be 

concluded that the urine concentrating capacity 

available is related to the aridity of the species’ 

habitat. 

Schoen, A. 1971. The effect of heat stress and water 

deprivation on the environmental physiology of 

bushbuck, reedbuck, and Uganda kob. East African 

Agricultural and Forestry Journal 37:1-7. 

Water balance, feed intake, urine osmolarity, and 

sodium and potassium levels in the urine were 

studied in the bushbuck (Tragelaphus scriptus 

dama), reedbuck (Redunca redunca wardi), and 

Uganda kob (Adenota kob thomasi). Animals 

were studied in a climate controlled laboratory 

under normal, heat stress, and dehydrated to levels 

at which their body mass was 85% of normal. 

Under heat stress all animals were able to 

maintain feed intake rates of normal levels. The 

bushbuck and kob showed good evaporative heat 

loss responses, and the reedbuck a poor response 

to heat stress. When dehydrated the urine 

electrolyte concentration increased by about 50% 

and fecal water loss were reduced by about 5% in 

the bushbuck, 27% in the reedbuck, and 38% in 

the kob. Potassium was the predominant cation 

excreted in the urine under all conditions. 

Schoen, A. 1972. Studies on the environmental 

physiology of a semi-desert antelope, the dik-dik. East 

African Agricultural and Forestry Journal 40:325-330. 

The water balance of the dik-dik (Rhyncotragus 

kirkii) was determined under normal and heat 

stress conditions and when the animal was 

dehydrated at a level at which its body weight was 

stabilized at about 85% of normal. The rectal 

temperature, respiration rate, urine osmolarity, 

and sodium and potassium level in urine was 

measured. The heat tolerance of the dik-dik was 

due mainly to a substantial heat storage capacity, 

the body temperature fluctuating over a range of 6 

oC above normal when under heat stress. The dikdik also demonstrated a very fast, shallow panting 

rate under heat stress, which reached nearly 400 

cycles min-1, 12 times the normal rate. When 

dehydrated and without an imposed heat load, the 

dik-dik made large economies in all water loss 

compartments, the urine could be concentrated to 

nearly 5,000 mOsm L-1, and evaporative water 

losses were reduced to about 60% of normal. 

Under heat stress or when dehydrated, fecal water 

losses were reduced from over 70 g 100 g-1 to 

around 55 g 100 g-1 of dry fecal matter. 

Shkolnik, A., A. Borut, and J. Choshniak. 1972. Water 

economy of the Bedouin goat. Symposia of the 

Zoological Society of London 31:229-242. 

The water economy of 5 Sinai Bedouin goats 

(body mass 11 – 22 kg) was studied in a hot room 

at a temperature of 30 oC, 30% relative humidity, 

with and without drinking water. Two black goats 

representing the breed commonly known as 

“mountain goat” were studied under the same 

experimental conditions for the purpose of 

comparison. Mountain goats are common all over 

Israel and thrive in the deserts of its eastern and 

southern regions. After two weeks of water 

deprivation, on a diet of dry hay and barley only, 

the Sinai goats lost about 30% of their body mass, 

but did not lose appetite. At the end of the first 

week under the same conditions, the mountain 
67 

goats lost about 25% of body mass and consumed 

no more food. Both breeds maintained body water 

content during the water deprivation period within 

levels normal to ruminants, and their drinking 

capacity, at the termination of the water 

deprivation period, was very high: 23 - 26% of the 

body mass in mountain goats and 30 - 40% in 

Sinai goats. When normally watered the water 

content in all body compartments was high in both 

breeds. The total water content amounted to 75 - 

78% of body mass and the blood plasma to 6 - 

8%. The Sinai goats, however, were more 

efficient in preserving water. The following 

features found in the Sinai goat may contribute to 

its efficient water economy: low metabolic rate, 

30% lower than the value predicted according to 

body mass; smaller evaporative water loss during 

water deprivation (541 mg water kg-1 hr-1

compared with 710 mg in the mountain goat); dry 

with only 40% water content and urine output per 

kg less than half that found in the mountain goat. 

The daily caloric value of the food consumed per 

day by the Sinai goat was a third of the intake per 

day by a mountain goat and the daily amount of 

water consumed by a Sinai goat was one fourth to 

one sixth the amount needed by a mountain goat 

although there is only a factor of two differences 

between the weights of the breeds. 

Shkolnik, A, E. Maltz, and S. Gordin. 1980. Desert 

conditions and goat milk production. Journal of Dairy 

Science 63:1749-1754. 

The influence of desert conditions on milk 

production was studied in the Black Bedouin goat. 

When goats were watered only once every 2 – 4 

days foraging rates increased. During water 

deprivation, goats lost 25 – 30 % of body mass 

from reductions in total body water and blood 

plasma volume. However, goats maintained 

relatively high milk production rates. Daily yields 

of over 2 kg have been reported for animals 

weighing 15 to 25 kg. Milk composition is similar 

to that of other goat breeds. Milk production 

efficiencies have exceeded 33% of energy 

consumed. Adaptation of the small Black Bedouin 

goat breed to arid desert conditions is also 

discussed. 

Siebert, B. D. and W. V. Macfarlane. 1971. Water 

turnover and renal function of dromedaries in the 

desert. Physiological Zoology 44:225-240. 

Water turnover and renal function of camels was 

studied using titrated water. The body water 

content of camels was similar to that of other 

ruminants; it was 8 – 23% greater in the summer 

than winter. Water turnover in summer was twice 

that observed in winter and was higher in lactating 

than in nonlactating animals. Urine flow of 

hydrated camels in summer decreases rapidly with 

water restriction. Water absorption in the 

reticulorumen is absorbed slowly and is not 

readily excreted by the kidney. During 

dehydration, potassium is excreted while sodium 

tends to be retained in the extracellular fluid and 

is used later to restore fluid volume. Glomerular 

filtration rate in dehydrated camels decreases to 

33% of the rate in hydrated camels resulting in 

very low urine flow rates of 0.5 – 1.5 ml min-1 are 

reached with urine concentrations of 2,000 – 

2,500 mOsm L-1. 

Siebert, B. D. and W. V. Macfarlane. 1975. Dehydration 

in desert cattle and camels. Physiological Zoology 

48:36-48. 

The effect of dehydration on body fluids, water 

turnover rates, fluid volumes, blood parameters, 

water metabolism, and hemolysis of red blood 

cells was studied in cattle and camels. Titrated 

water, blood extraction, collection of urine and 

feces were used in this study. The body mass of 

cattle decline more (6.1% vs. 2.1%) than camels 

when both species were dehydrated. Cattle lost 

twice as much fluid from plasma than camels. 

Urine flow of dehydrated camels was lower and 

less variable than dehydrated cattle. Dehydrated 

cattle also had higher fecal moisture contents than 

dehydrated cattle. 

Silanikove, N. 1985. Effect of dehydration on feed 

intake and dry matter digestibility in desert (Black 

Bedouin) and non-desert (Swiss Saanen) goats fed on 

Lucerne hay. Comparative Biochemistry and 

Physiology 80A:449-452. 
68 

The effect of dehydration on feed intake and dry 

matter digestibility in Black Bedouin and Swiss 

Saanen goats fed on Lucerne hay were studied 

during mid-summer in a captive herd in the 

research zoo at Tel-Aviv University, Israel. Food 

consumption decreased with the lengthening of 

the period of dehydration in both breeds in a 

similar manner. However, the Saanen goats 

reduced their dry matter intake and consequently 

their water intake much more than Bedouin goats. 

The apparent dry matter digestibility increased 

significantly in both breeds during dehydration, 

the response being larger in the Saanen goats. 

Bedouin goats were capable of maintaining during 

3 days of dehydration a level of consumption, 

which is well above their maintenance 

requirements while the Saanen goats consumed 

only the amount of feed, which is needed to 

satisfy their maintenance requirements. 

Singh, N. P., T. More, and K. L. Sahni. 1976. Effect of 

water deprivation on feed intake, nutrient digestibility, 

and nitrogen retention in sheep. Journal of Agricultural 

Science 86:431-433. 

This paper describes the effect of water 

deprivation on nutrient digestibility and nitrogen 

retention in sheep. Thirty-six female sheep were 

divided into 3 groups, a group watered every 24 

hr, a group watered every 48 hr, and a group 

watered every 72 hr. Maximum and minimum 

temperatures ranged between 21 and 24.8 C. The 

water and dry matter intake was 5.5 and 2.6% of 

body mass in the daily watered group, 5.5 and 

2.1% in the group watered every 48 hr, and 4.8 

and 2.2% in the group watered every 72 hr. Dry 

matter intake was significantly reduced when 

females were watered every 48 and 72 hr than in 

sheep watered every 24 hr. However, there was no 

difference in dry matter intake between groups 

watered 48 hr and 72 hr. Digestibility of dry 

matter, crude protein, ether extract, and crude 

fiber was highest in the group watered every 48 

hr. Nitrogen intake was 22.1, 20.1, and 20.4 g 

animal-1 day-1 for the 24, 48, and 72 hr groups, 

respectively. The animals in the three groups lost 

24.2, 20.4, and 26.3% of the total nitrogen intake 

through the feces and 29.1, 23.5, 27.1% through 

the urine. 

Skadhauge, E., E. Clemens and G. M. O. Maloiy. 1980. 

The effect of dehydration on electrolyte concentrations 

and water content along the large intestine of a small 

ruminant: the dik-dik antelope. Journal of Comparative 

Physiology 135B:165-173. 

The concentrations of Na, K, and Cl and the water 

content in the large intestine and rectum of an 

East African ruminant, the dik-dik antelope 

(Rhynchotragus kirkii) was investigated in 

hydrated and dehydrated animals. Intestinal 

contents were removed at 6 sites along the large 

intestine and rectum, and the water fraction and 

the amount of Na, K, and Cl were measured per g 

dry matter. An impermeant water marker showed 

that the dry matter amount was nearly constant 

along the lower gut. Local electrolyte absorption 

rates were determined in the terminal colon using 

a dialysis bag method. Approximately 4/5 of the 

absorption of NaCl and water took place in the 

upper large intestine. Throughout the lower gut 

the Na concentration of the absorbate was close to 

that of plasma. The Na and Cl concentrations of 

the digesta decreased while the K concentration 

rose, but K was still absorbed. Dehydration 

resulted in a reduction of 35% of the water lost 

per gram of dry matter. The water content was 

reduced from the start of the large intestine (by 

13%), but the fractional absorption of salt and 

water in the large intestine and rectum was not 

significantly changed. The local electrolyte 

absorption rates and the electrical potential 

difference were slightly reduced. The Na and K 

concentrations of the absorbate remained nearly 

constant. The water saving during dehydration 

thus seems to proceed without specific 

adjustments of the transport parameters of the 

lower gut. The concentrations of Na and Cl in 

approached those, which in dialysis bag 

experiments, result in zero absorption of NaCl and 

water in the lower gut at different flow rates of 

dry matter. 

Skatan, J. E. and O. Holand. 1989. Water turnover 

during winter in roe deer. International Union Game 

Biologists 19:191 (Abstract). 

Water transfer rate was studied in 9 captive roe 

deer (Capreolus capreolus) by tritium water 

dilution technique. Six roe deer were feed 4 
69 

different diets: marrow stem kale, commercial 

livestock feed, fresh bilberry stems, and grains of 

oat, through sequential periods. Marrow stem kale 

diet gave the highest water transfer rates (259 ml 

kg-0.8 body mass day-1) and oats the lowest (68 ml 

kg-0.8 body mass day-1). In three roe deer fed the 

commercial livestock feed only, the water transfer 

rate and dry matter intake decreased from October 

to December. Ambient temperature was <0 oC. 

From December to February the dry matter intake 

continued to decrease for this group, but the water 

transfer rate remained at the same level. Ambient 

temperatures in this period were >0 oC. This might 

indicate that the water transfer rate depends both 

on ambient temperature and seasonal variations in 

food intake. 

Smith, B. S. and A. R. Sykes. 1974. The effect of route 

of dosing and method of estimation of titrated water 

space on the determination of total body water and the 

prediction of body fat in sheep. Journal of Agricultural 

Science 82:105-112. 

Eight mature female sheep were offered a ration 

that maintained body mass constant during a 20-

week period. During the final 10 weeks a 

comparison was made in each animal of the 

pattern of equilibration and urinary losses of 

titrated water during 8 hr after dosing by four 

different routes. These were intravenous, 

intraperitoneal, intraruminal, and a combination of 

the intraperitoneal and intraruminal routes. 

Titrated water spaces were calculated from (a) the 

8-hr plasma specific activity and (b) by 

extrapolation to zero time of the plasma specific 

activities during the 7 days after injection. At the 

end of the experiment the fat and water contents 

of the bodies of the sheep were determined 

directly. Complete equilibration of titrated water 

between plasma and rumen water was not 

achieved in all animals 8 hr after intravenous or 

intraperitoneal injection but was when the rumen 

was primed by the combination of intraperitoneal 

and intraruminal dosing. After intraruminal dosing 

equilibration was not achieved in any animal 

within 8 hr of dosing. Urinary losses of marker 

were lower after intraruminal dosing but 

otherwise averaged 4 – 5% of the dose L-1 urine. 

This was equivalent to 0.3 – 6.7% of the dose for 

individual sheep. Errors resulting from incomplete 

equilibration and urinary loss of marker did not 

influence the efficiency of prediction of total body 

water from titrated water space. The multiple 

correlation coefficient relating body fat with 

empty body weight and its water content was very 

high (r = 0.99). Errors introduced into this 

relationship by the inclusion of gut water in the 

prediction equations were apparently of a similar 

magnitude to those resulting from the errors in the 

estimation of titrated water space. The 

extrapolation method for the determination of 

titrated water space was shown to have the same 

accuracy as equilibration techniques under these 

controlled dietary 

conditions. 

Sneddon, J. C., J. Van der Walt and G. Mitchell. 1991. 

Water homeostasis in desert-dwelling horse. Journal of 

Applied Physiology 71:112-117. 

This study set out to investigate tolerance of the 

body water pool to short-term water deprivation in 

horses and, in particular, to assess whether feral 

horses from the Namib Desert showed tolerance 

to dehydration superior to Transvaal. Hydration 

status was compared in 6 feral horses from the 

Namib Desert and 6 Boerperd farm horses under 

conditions of normal hydration and after 72 hr of 

dehydration. Under normal hydration, the 2 

groups did not differ significantly in water intake, 

plasma sodium and potassium concentrations, 

plasma osmolality, hemocrit, total plasma protein, 

body water content, or water turnover. The Namib 

horses were significantly smaller and turned over 

5 L less water pre day than the Boerperd during 

normal hydration and turned over 4 L less during 

dehydration. Increases in plasma sodium 

concentration after 72 hr dehydration were greater 

in the Namib horses. It was concluded that horses 

can easily tolerate water deprivation that results in 

12% reduction in body mass. The feral horses of 

the Namib Desert were not significantly different 

per unit mass from domestic horses with regard to 

indexes of total body water content under 

conditions of normal hydration and after 72 hr of 

dehydration. Their smaller size and, hence, lower 

water turnover might be mechanisms they use for 

survival in the Namib Desert. 
70 

Sneddon, J. C., J. Van der Walt and G. Mitchell. 1993. 

Effect of dehydration on the volumes of body fluid 

compartments in horses. Journal of Arid Environments 

24:397-408. 

Maintenance of plasma volume during 

dehydration is essential for survival in mammals. 

Supplemental fluid may be drawn from the 

interstitial, intracellular and transcellular 

(primarily gastrointestinal) compartments. We 

have studied the changes in the volumes of these 

compartments in arid-adapted (Namib) and in 

subtropical farm horses from the Transvaal 

(Boerperd) in response to dehydration, in order to 

identify mechanisms which protect plasma 

volume in these horses. As a fraction of total fluid 

loss, 6% was lost from the plasma, 27% from the 

interstitial space, and 67% from the combined 

intracellular/transcellular space. The Namib 

horses showed a tendency to lose, as a fraction of 

total fluid loss, more fluid from the interstitial 

space (29%) and less from the transcellular space. 

The Namib horses showed a tendency to lose, as a 

fraction of total fluid loss, more fluid from the 

interstitial space (29%) and less from the 

transcellular space (65%) than the Boerperd (21% 

and 73% respectively). The Namib horses 

absorbed intestinal fluid more rapidly than the 

Boerperds, as indexed by a larger difference in 

tritium content of the body water pool, between 

the dehydrated and rehydrated states, over the 

same period of rehydration. This difference was 

not significant (P<0.115). We conclude that hoses 

maintain their plasma volume effectively, as do 

arid-adapted species such as donkeys, camels, 

desert sheep and goats during acute dehydration, 

and that Namib horses tended to be more 

competent in this respect than Boerperd. 

Soldatova, N. V. and A. V. Grazhdankin. 1989. 

Evaporative water losses in goitred gazelle (Gazella 

subgutturosa). Zoologicheskii Zhurnal 68:102-109. (In 

Russian with English summary). 

Coat water-vapor conductance in goitred gazelle 

is similar to that one whose skin does not have 

sweat glands. In young goitred gazelles cutaneous 

evaporation intensity is 12.1 g m2-1 hr-1 on the 

back surface and 8.6 g m2-1 hr-1 on the abdomen. 

In adult females these parameters are 10.0 and 

11.5 g m2-1hr-1 accordingly. Age differences in the 

cutaneous conductance are probably related to a 

different wool structure. With the air temperature 

up to 36 oC and skin temperature up to 39.5 oC 

cutaneous water evaporation goes mainly through 

diffusion and with higher temperatures, 

evaporation through sweat glands dramatically 

increases the water loss. No age differences were 

found in the intensity of pulmonary evaporation. 

With a moderate heat load young goitred gazelles 

lose about 25% of their metabolic thermoproducts 

through the evaporation diffusion and with an 

elevated heat load and panting about 45%. The 

share of pulmonary evaporation in the total 

evaporative water loss is 25 - 50%. Experimental 

findings indicate that goitred gazelles have two 

forms of adaptation bridging mechanisms of 

thermoregulation and water balance regulation. 

One of them allows gazelles to prevent an 

excessive dehydration with a moderate heat load, 

the other provides and effective use of the 

evaporative water loss for body cooling with 

elevation of ambient temperature. 

Soppela, P., M. Nieminen, and S. Saarela. 1992. Water 

intake and its thermal energy cost in reindeer fed lichen 

or various protein rations during winter. Acta 

Physiologica Scandinavica 145:65-73. 

Captive reindeer were fed four different rations 

which supplied equal energy but varying amount 

of crude protein: lichen (3%), mixed hay plus 

lichens (10%) and 2 feed concentrations with 

medium (12%) of high (18%) protein content. 

Kinetics of total body water were measured with 

titrated water from February to March 1985, and 

thermal energy cost of daily water intake was 

estimated. Biological half-time of water was 

shorter, and daily water intake significantly higher 

on the hay plus lichens diet and on the medium- or 

high-protein concentrates diet than on the lichen 

diet during March 1985. Similar differences were 

found between reindeer on medium-protein 

concentrate and on lichens at the end of the 

corresponding feeding period during April 1986. 

Daily water inflow was positively correlated with 

a dietary supply of digestible crude protein (r = 

0.916). Thermal energy costs of daily water intake 

were highest 1.9 MJ 3.7 L-1 in reindeer on highprotein concentrate during March 1985, and 2.0 
71 

MJ 3.9 L-1 in reindeer on medium-protein 

concentrate during April 1986. The reindeer fed 

on lichens had minimal and nearly twice as small 

thermal energy cost of daily water intake (mean 

1.1 MJ 2.1 L-1) as on either of the concentrates. 

Our results show that even a moderate feed 

protein ration can significantly increase free water 

intake and its thermal energy cost in reindeer as 

compared to dominant natural feed (lichens) 

during winter. Careful protein supplementation is 

recommended to support body condition with a 

concomitant addition of easily soluble 

carbohydrates to compensate for increased 

thermal costs of water intake. 

Springell, P. H. 1968. Water content and water turnover 

in beef cattle. Australian Journal of Agricultural 

Research 19:129-144. 

Twenty-four steers, comprising British (Hereford 

and Hereford X Shorthorn), Zebu (Africander), 

and Zebu cross (British X Brahman or Africander) 

breeds, were either maintained on pasture, or 

yarded and fed diets of a low and a high 

nutritional value. Titrated water was injected into 

the animals on 5 occasions at intervals of 3 

months. The body water content and the water 

turnover rate were calculated, and some of the 

sources of variation defined. Observed differences 

in the water content are attributable to nutritional 

factors rather than to breed differences. The mean 

body water content ranged from 615 to 809 ml kg1

 fasting body mass, where higher values were 

associated with a poor diet. The mean half-life of 

titrated water was lower in summer (as low as 58 

hr) than in winter (up to 128 hr) in grazing and 

well-fed yarded steers. On a poor diet, however, 

the half-life in yarded cattle remained high and 

almost constant throughout the year, dropping to 

below 100 hr on only a single occasion. 

Occasionally the half-life was breed dependent, 

but generally no significant differences between 

breeds could be found. While mean turnover rates 

of up to 7.1 ml kg-1 hr-1 were found in better–fed 

cattle in summer, the value in poorly fed animals 

was almost constant throughout the year at about 

3.3 ml kg-1 hr-1. There was, however, a winter 

minimum in the well-fed yarded and grazing 

groups. The turnover rate was influenced by breed 

only to a limited extent. The results are interpreted 

in light of their possible significance in the 

adaptation to a tropical environment, and in 

relation to their value in predicting body 

composition. 

Syrjala, L., J. Salonen, and M. Valtonen. 1980. Water 

and energy intake and nitrogen utilization in reindeer. 

Pages 252-261 in Reimers, E., E. Garre, and 

Skjenneberg, editors, Proceedings of the Second 

International Reindeer/Caribou Symposium, Roros 

Norway. 

The influence of energy intake on nitrogen 

utilization and water requirements in reindeer 

(Rangifer tarandus) was studied over 4 winters 

between 1974 and 1977. Five digestibility and 

nitrogen balance trials were carried out, in 

digestibility cages where all feces and urine were 

collected, using a Latin Square design at air 

temperature of 10 oC. Six different rations were 

offered with mean crude protein concentration 

ranging from 3.3 to 15.3%. The average crude 

protein, metabolizable energy, and total water 

intakes per day were 97 ± 38 g, 2.2 ± 0.5 Mcal, 

and 3,160 ± 1,040 g (mean ± SD), respectively. 

Protein utilization was strongly limited by the 

insufficient energy intake. Total water intake was 

highly positively correlated to the crude protein 

intake (CPI) (r = 0.787, P < 0.001) and urine 

excretion of nitrogen (r = 0.758, P < 0.001). On a 

negative nitrogen balance the water intake still 

increased slightly with extra nitrogen excretion. 

Urine nitrogen concentration on the different 

rations remained almost constant, but the urine 

volume was significantly correlated with total 

urine nitrogen. Total water required by reindeer 

can be calculated from the equation TWI = 21.5 x 

CPI + 1,080. 

Taneja, G. C. 1973. Water economy in sheep. Pages 

95 – 132 in H.F. Maryland, editor Proceedings of wateranimal relations. Twin Falls, Idaho. 

A series of experiments were conducted to find 

out the ill effects of prolonged water deprivation 

and to work out a watering schedule, which 

should save water expenditure and at the same 

time should not affect the animal’s health 

adversely. Sheep deprived of water for 5 days 

during summer lost and average of 25% of body 
72 

weight, rectal temperature rose, respiratory rate 

decreased 20%, and plasma volume decreased 

22%. Ill effects were not observed in sheep when 

at least 75% of normal water intake was 

maintained. In desert areas where Prosopis 

spicigera were in abundance, sheep drew much of 

their water supply by eating the pods of these 

trees, which contained 68% water during summer. 

In these experiments, sheep eating these pods 

lived without water for 12 days and did not show 

any loss in body mass. When sheep were deprived 

of water for 3 days there was a 50% reduction in 

plasma volume. It seems therefore, sheep does not 

have any mechanism of retaining the circulatory 

fluid during dehydration. 

Taylor, C. R. 1968a. Hygroscopic food: A source of 

water for desert antelopes. Nature 219: 181-182. 

Observations of diet selection of the oryx (Oryx 

besia) and Grant’s gazelle (Gazella granti) and 

measurements of ambient temperature and relative 

humidity (RH) were recorded in 1965 on the El 

Barta Plains in the Northern Frontier Province, 

Kenya. Plants eaten by oryx and Grant’s gazelle 

were collected throughout the day. The diet of 

oryx and Grant’s gazelle consisted primarily of 

Disperma sp. Disperma sp. samples were 

collected and dried until a constant weight was 

obtained, they were then placed in 3 

environments: 17 oC, 85% RH; 23 oC, 39% RH; 

and 40 oC, 17% RH and the samples were 

weighed hourly to determine weight gain from 

absorption of moisture from air. Leaves in the 17 

oC environment equilibrated after 10 hr with 42% 

water content, leaves in the 23 oC equilibrated 

after 2 hr with 39% water, and leaves in the 40 oC 

environment equilibrated after 2 hr with 2% 

water. By adjusting their foraging times and 

feeding at night and the early morning, oryx and 

Grant’s gazelle would be able to obtain more 

preformed water from the same plants than if they 

fed at midday. 

Taylor, C. R. 1968b. The minimum water requirements 

of some East African bovids. Symposium of the 

Zoological Society of London 21:195-206. 

Several of the wild East African bovids are 

reported to be capable of surviving in arid regions 

without drinking. Minimum amounts of water 

required by eland (Taurotragus oryx), oryx (Oryx 

besia), and Grant’s gazelle (Gazella granti), 

whose ranges include the hot arid sub-Sahara, are 

compared with the amounts required by buffalo 

(Syncerus caffer), wildebeest (Connocaetes 

taurinus), and Thomson’s gazelle (Gazella 

thomsonii), whose ranges are limited by water 

availability. Frequent droughts have provided a 

severe selection pressure for frugal use of water 

during the relatively short period in which zebu 

cattle have been resident in East Africa. Thus the 

water requirements of these animals provide a 

yardstick for evaluation the rate at which water 

conserving mechanisms evolve, while the water 

requirements of the temperate Hereford steer as a 

baseline against which to judge the efficiency of 

these mechanisms in other species. Studies were 

carried out in a climate-controlled room with an 

intermittent heat load, enabling one to evaluate 

adaptations for dealing with both heat and aridity. 

Oryx, Grant’s gazelle, Thomson’s gazelle, and 

zebu cattle are found to be specialized for 

conserving water and can maintain a constant 

weight on a total water input of approximately 2% 

of their body mass day-1 (in an environment of 22 

oC). Hereford steers require more than twice this 

amount of water. Zebu cattle are more specialized 

physiologically for coping with arid conditions 

than the eland, wildebeest, or buffalo. The eland, 

however, is able to gain independence of surface 

water by behavioral and physiological means 

other than conservation of water. In contrast, the 

Thompson’s gazelle, which requires extremely 

small amounts of water, is unable to inhabit the 

hot arid regions of East Africa for reasons yet to 

be explained. The development of water sparing 

mechanisms is only one aspect of the complex of 

adaptations that determines the limits of a species’ 

range. 

Taylor, C. R. 1969a. The eland and the oryx. Scientific 

American 220:88-95. 

The thermoregulation and water balance were 

studied in the eland (Taurotragus oryx) and the 

oryx (Oryx biesa) in a controlled environment 

with 12 hr of 40 oC and 12 hr of 22 oC. The oryx 
73 

and eland were provided ad libitum water and 

rectal temperatures were measured. Both species 

allowed their body temperatures to rise (7 oC in 

the eland and 6 oC in the oryx) before beginning 

to use evaporative cooling. Both species were then 

dehydrated until their weighed 85% of their 

original weight, then exposed to the same 

conditions. The eland maintained a body 

temperature lower than ambient temperature 

whereas the oryx’s body temperature regularly 

rose above ambient temperatures. The mechanism 

involving counter current heat exchange that 

allows these animals to allow increases in body 

temperature while maintaining brain temperatures 

lower than those of the body. The metabolic rates 

of hydrated and dehydrated eland and oryx were 

also determined. Both species decreased their 

metabolic rates when dehydrated, the oryx more 

than the eland. It was also found that both species 

were able to reduce pulmonary water loss at night 

by extracting more oxygen from each breath and 

breathed more slowly. The feeding habits and diet 

are also discussed relative to plant moisture 

content. 

Taylor, C. R. 1969b. Metabolism, respiratory changes 

and water balance of an antelope, the eland. American 

Journal of Physiology 217:317-320. 

The eland (Taurotragus oryx) and African zebu 

steer were used to assess oxygen consumption, 

respiratory volume, and respiratory water loss in a 

controlled laboratory setting in Muguga, Kenya. 

In experiments at 14 oC, a temperature often 

encountered at night, the oxygen consumption of 

the eland was 19% higher than at 22 oC. 

Ventilation volume, however, was unchanged. 

Furthermore, respiratory evaporation was less, 

since body temperature and therefore the amount 

of water contained in the saturated expired air 

decreased. The African zebu steer also increased 

its oxygen consumption at 14 oC (by 28%), but its 

body temperature was more constant and 

ventilation volume and respiratory water loss 

increased. 

Taylor, C. R. 1970a. Dehydration and heat: effects on 

temperature regulation of East African ungulates. 

American Journal Physiology 219:1136-1139. 

This study investigated the effects of dehydration 

on rectal temperature and evaporative cooling at 

air temperatures up to 50 oC in both desert and 

nondesert species. Six species of East African 

ungulates, Grant’s gazelle (Gazella granti), 

Thomson’s gazelle (G. tompsonii), oryx (Oryx 

beisa), wildebeest (Connocaetes taurinus), zebu 

steer, and African buffalo (Syncerus caffer), were 

selected on the basis of size, habitat, and whether 

they sweated or panted to dissipate excess heat. In 

all species dehydration caused an increase in the 

air temperature at which animals would begin to 

sweat or pant. Steady-state rectal temperatures 

were higher and rates of panting or sweating were 

lower in dehydrated than in hydrated animals. The 

magnitude of these effects was greater in desert 

than in nondesert species. At 45 oC air 

temperature, rectal temperature of the 2 desert 

species, Grant’s gazelle and oryx, exceeded air 

temperature by between 0.5 and 2 oC, and rectal 

temperature of 46.5 oC could be maintained for 6 

hr without observable ill effects. 

Taylor, C. R. 1970b. Strategies of temperature 

regulation: effects on evaporation in East African 

ungulates. American Journal Physiology 219:1131-

1135. 

This study investigated the effects of 

physiological adaptations for temperature 

regulation on water loss in 8 species of African 

ungulates, 3 desert-dwelling species, Grant’s 

gazelle (Gazella granti), eland (Taurotragus 

oryx), and oryx (Oryx beisa), and 3 species that do 

not inhabit arid regions, Thomson’s gazelle (G. 

thomsonii), wildebeest (Connocaetes taurinus), 

and African buffalo (Syncerus caffer), and 2 

species of domestic ungulates, zebu steer, and 

Hereford steer. All species were subjected to 

simulated desert conditions (12 hr at 40 oC) 

alternating with 12 hr at 22 oC in the laboratory. 

Water loss was assessed via a total water balance 

method where the total intake of free water, 

preformed water, and estimates of metabolic 

water was assessed versus the amount lost in feces 

and urine. Under these temperature regimes with 

both ad libitum access to water and water 

restriction 2 strategies were found in desertdwelling species to reduce water loss during 

periods of water restriction. Large ungulates, such 
74 

as the eland have low body temperatures in the 

morning and slowly increase throughout the day; 

this mechanism reduces the need to increase water 

loss for temperature regulation. Conversely, small 

ungulates, such as Grant’s gazelle, allow their 

body temperatures to quickly rise above ambient 

temperatures eliminating the need to pant or sweat 

to reduce heat loads. Intermediate size ungulates 

use a combination of these 2 strategies. 

Taylor, C.R.. 1972. The desert gazelle: A paradox 

resolved. Symposia of the Zoological Society of London 

31:215-227. 

Water physiology of Grant’s (Gazella granti) and 

Thomson’s gazelle (G. thomsonii) were studied in 

metabolic cages. The range of the Grant’s gazelle 

however, extends into the hot, arid regions of East 

Africa while that of the Thomson’s gazelle does 

not. Grant’s gazelle requires about 33.3% more 

water per kg body mass than the Thomson’s 

gazelle in a simulated desert environment (12 hr 

day-1 at 22 oC alternating with 12 hr day-1 at 40 

oC). This paper tries to resolve this apparent 

paradox by investigating the response of the 2 

gazelles to short, but very intense, heat loads. 

Most of the water loss in a simulated desert is 

through evaporation and helps keep the animal 

cool. Intense solar radiation occurs together with 

high air temperatures in the arid regions of Africa. 

During a short period at mid-day, Grant’s gazelle 

might frequently encounter a more severe heat 

load than the air temperature of 40 oC provided in 

the simulated desert. At high ambient air 

temperatures both gazelles dissipate heat 

primarily by panting. When dehydrated neither 

gazelle began to pant until air temperatures 

exceeded 40 oC and steady state rectal temperature 

was higher than air temperature. This effect was 

greater in the desert-dwelling Grant’s gazelle than 

in the Thomson’s gazelle. For example, when air 

temperature was 45 oC body temperature of the 

Grant’s gazelle was as high as 46.5 oC while that 

of the Thomson’s gazelle did not exceed 42.3 oC. 

The higher body temperature and lower 

evaporation of the Grant’s gazelle at air 

temperatures exceeding 40 oC help to resolve the 

apparent paradox between water requirements and 

habitat of the gazelles. 

Taylor, C. R. and C. P. Lyman. 1967. A comparative 

study of the environmental physiology of an East 

African antelope, the eland and the Hereford steer. 

Physiological Zoology 40:280-295. 

The water requirements and physiological 

adaptations to arid environments were studied in 

the eland (Taurotragus oryx) and Hereford steer 

were studied under laboratory conditions. Water 

intake, turnover, evaporative water loss, oxygen 

consumption, respiratory water loss, and 

minimum water requirements were determined at 

22 and 40 oC. Overall average water loss did not 

differ between eland and Hereford steer, however 

the routes of water loss did differ between species. 

Hereford steer had higher fecal water loss than the 

eland. Variations in body temperature were much 

higher in the eland than in the Hereford steer. The 

eland also had a narrower thermoneutral zone than 

the Hereford steer. 

Taylor, C. R. and C. P. Lyman. 1972. Heat storage in 

running antelopes: independence of brain and body 

temperatures. American Journal of Physiology 222:114-

117. 

This study tried to determine how much of this 

heat was stored and to find out if antelopes 

possess unusual physiological mechanisms for 

coping with high body temperatures when 

antelope run at high speeds. Large increases in 

rectal temperature of Thomson’s gazelles (Gazella 

thomsonii, wt 15 kg) were measured during 

running: +3.9 oC after 5 min at 40 km hr-1; +4.6 oC 

after 11 min at 25 km hr-1; and +4.3 oC after 20 

min at 15 km hr-1. Heat storage accounted for 80 - 

98% of the calculated heat production during 

running. Brain temperature rose more slowly than 

rectal or carotid artery temperature. After a 5 min 

run at 40 km hr-1, the brain was 2.7 oC cooler than 

blood in the carotid artery. Blood supplying the 

brain appears to be cooled via a countercurrent 

heat exchange with cool blood draining the nasal 

mucosa (in the carotid rete). Elands (Taurotragus 

oryx, mass 200 kg) sweated profusely and their 

rectal temperature equilibrated after a few minutes 

of running at a slightly higher level: +0.8 oC at 25 

km hr-1; 0.8 oC at 20 km hr-1; +0.7 oC at 15 km 

hr-1; and +0.5 oC at 10 km hr-1. 
75 

Taylor, C. R., C. Spinage, and C. P. Lyman. 1969a. 

Water relations of the waterbuck, an East African 

antelope. American Journal of Physiology 217: 630-

634. 

The water relations of the waterbuck (Kobus 

defassa) was studied in a climate controlled 

laboratory setting. We found that in a moderate 

environment (22 oC) the waterbuck required 25% 

more water than a domestic Hereford steer. At 40 

oC the waterbuck lost water equal to about 12% of 

its body mass in 12 hr. This degree of dehydration 

could not be tolerated for prolonged periods at 40 

oC. When water intake was restricted, fecal water 

loss was reduced, but urine volume and 

evaporation were unchanged. Oxygen 

consumption was not altered by dehydration and 

this helps explain the relatively unchanged water 

loss with the restricted water intake. The 

unusually high water requirement of the 

waterbuck is in accord with its restricted habitat 

near water. 

Taylor, C. R., D. Robertshaw, and R. Holmann. 1969b. 

Thermal panting: a comparison of wildebeest and Zebu 

cattle. American Journal of Physiology 217:907-910. 

Thermal panting of wildebeest (Connochaetes 

taurinus) and Zebu cattle was studied under 

laboratory conditions. At 50 oC both wildebeest 

and zebu cattle maintained their rectal 

temperatures about 10 oC below ambient 

temperature. At higher air temperatures, 

preventing cutaneous evaporation had no 

observable effect on the wildebeest’s ability to 

regulate its temperature whereas it seriously 

impaired the zebu’s ability. The wildebeest 

developed respiratory alkalosis only at air 

temperatures of about 50 oC whereas in the zebu, 

with cutaneous evaporation blocked, this 

happened at about 43 oC. To avoid alkalosis the 

wildebeest could increase its effective dead space 

as it pants. Morphological studies indicate that the 

wildebeest have a larger anatomical dead space, 

larger nasal passages, and larger openings into the 

paranasal sinuses than cattle. Ventilation of the 

paranasal sinuses may contribute to increased 

dead space as the wildebeest pants. 

Taylor, C. R. and G. M. O. Maloiy. 1967. The effects of 

dehydration and heat stress on intake and digestion of 

food in some east African bovids. International 

Congress of Game Biologists 8:324 (Abstract). 

The effect of an intermittent heat load (a daily 

cycle of 12 hours at 22 oC and 12 hours at 40 oC) 

and a 15% level of dehydration, with ad without 

the heat load, on food intake and digestibility of a 

poor quality hay was investigated in the Grant’s 

gazelle (Gazella granti), and oryx (Oryx beisa); 

the arid domestic Turkana goats, fat-tailed sheep, 

and zebu cattle, and the non-arid Thomson’s 

gazelle (G. tompsonii), and wildebeest 

(Connocaetes taurinus). An intermittent heat load 

with water available ad libitum depressed the food 

intake of zebu cattle and Turkana goats more than 

40%. It had no significant effect on intake of any 

of the other species. Dehydration at 22 oC caused 

a depression in food intake of all the species 

investigated. Dehydration together with heat load 

caused no further reduction in food intake of the 

arid Grant’s gazelle and oryx, or in goats but did 

cause a further reduction in the other species. The 

digestibility of food by the Thomson’s gazelle is 

found to be much higher than that of any other 

species. 

Taylor, C. R., R. Dmi’el, A. Shkolnik, D. Baharav, and 

A. Borut. Heat balance of running gazelles: strategies 

for conserving water in the desert. American Journal of 

Physiology 226:439-442. 

The effect of exercise on water balance of 

mountain gazelle (Gazella gazella) was 

determined in the laboratory. Heat lost through 

evaporation, Nonevaporative means, and the 

amount stored as animals rested at various air 

temperatures and ran at various speeds was 

determined. The same proportion of the heat 

production was lost by evaporation at 3 km hr-1 as 

at rest, whereas 30 – 40% more of the heat 

produced while running at 6 – 9.5 km hr-1 was lost 

by evaporation. At speeds exceeding 15 km hr-1, 

most of the heat produced was stored. However, 

when the recovery period after a sprint was 

included (while body temperature returned to 

normal levels), the same proportion of the heat 

production was lost by evaporation as at rest. 

Since gazelles normally either move slowly as 
76 

they graze or sprint to avoid predators, it seems 

reasonable to conclude that exercise would not 

have a major effect on their water balance. 

Thorton, R. F. and H. G. Yates. 1968. Some effects of 

water restriction on apparent digestibility and water 

excretion in cattle. Australian Journal of Agricultural 

Research 19:665-672. 

An experiment is described in which digestibility 

and water excretion was investigated in cattle 

using metabolism crates during periods of 

unrestricted feed and water, of water restriction, 

and of feed restriction. During water restriction, 

increased dry matter and acid detergent fiber 

digestibilities could not be wholly accounted for 

by decreased intake of dry matter. Reduced fecal 

water output was more important than changes in 

urine output in conserving water. It is suggested 

that the hindgut has a regulatory role in the 

observed responses to water restriction. 

Thorton, R. F. and H. G. Yates. 1969. Some effects of 

water restriction on nitrogen metabolism of cattle. 

Australian Journal of Agricultural Research 20:185-189. 

The effect of water restriction on the metabolism 

of nitrogen was studied in cattle using metabolism 

crates. Water restriction was found to decrease 

nitrogen retention in cattle when compared with 

periods of similar digestible energy intake but 

unrestricted water intake. The decreased nitrogen 

retention was associated with increases in fecal 

nitrogen output and urinary excretion. The rise in 

urinary urea nitrogen excretion appeared to be 

mediated through increased plasma urea nitrogen 

concentration. 

Till, A. and A. Downes. 1962. The measurement of total 

body water in sheep. Australian Journal of Agricultural 

Research 13:335-342. 

The measurement of total body water in sheep 

was studied. After intravenous injections of 

titrated water were given to sheep, about 5 hr was 

required for the dose to equilibrate with the total 

body water. A standard procedure for estimating 

the total body water of sheep was adopted, in 

which blood samples were taken 6 and 7 hr after 

an intravenous injection of titrated water. The 

specific activity of the water from the 2 samples 

was measured and the mean value used for the 

calculation of total body water. As a result of a 

study of the errors in this method, it was 

concluded that the value obtained for the total 

body water in about 2% of the body mass higher 

than the true value, and on measuring the rate of 

fall in specific activity of the total body water. 

This specific activity fell exponentially with time, 

with turnover half-times ranging from 3.5 to 16.3 

days for sheep housed indoors. 

Tomkiewicz, S. M. 1979. Heterothermy and water 

turnover in feral burros (Equus asinus) of the desert 

southwest. Masters thesis, Arizona State University, 

Tempe, Arizona, USA. 

Body temperature and subcutaneous temperature 

of 5 free-ranging and 15 captive burros were 

monitored by temperature sensitive implants. 

Body temperature and subcutaneous temperature 

were related to environmental parameters and 

activity. Titrated water turnover rates were 

monitored on 2 free-ranging and 12 captive 

burros. Relationships between season, age, and 

body weight were examined. Burros exhibited a 

pronounced heterothermy (35.0 – 41.6 oC). Mean 

body temperature was lower in free-ranging 

burros than in captive burros. In both free-ranging 

and captive burros, body temperature was 

dependent on time of day and air temperature. 

Males maintained consistently lower body 

temperature (mean 36.5 oC) than females (mean 

38.2 oC) in summer. During summer, burros 

remained quiescent throughout most of the day 

and were active nocturnally. Males engaged in 

more strenuous activities during periods of 

maximum summer heat load than did females. 

Fighting or copulation resulted in a rapid increase 

in body temperature of males (0.1 oC min-1). 

During winter, activities were not restricted 

during the daytime and burros were observed at 

greater distances from permanent water. A sexual 

difference in body temperature did not exist in 

winter. Water turnover rates were higher in 

summer than winter. Absolute water loss 

increased with age and weight during summer and 

winter. Weight specific water loss increased with 
77 

age and weight in summer; however, in winter, 

weight specific water loss was lower in colts than 

in adults. An ecophysiological model was 

developed to explain the breeding biology of feral 

burros in the desert southwest. 

Turner, J. C. 1973. Water, energy, and electrolyte 

balance in the desert bighorn sheep, Ovis canadensis, 

Ph. D. Thesis, University of California, Riverside, 

California, USA. 132 p. 

Bighorn sheep were studied in the Santa Rosa 

Mountains, California. Animals were captured 

and maintained in an enclosure; water and energy 

requirements, seasonal changes in body fluid 

distribution, and effects of water deprivation on 

food consumption, body temperature, excretion, 

and distribution of body fluids were determined. 

Captive animals had daily water requirements 

equivalent to 3 - 4% of their body mass during the 

summer. During winter and spring daily water 

requirements were 1 - 2% of body weight. 

Seasonal investigations of water balance were 

determined by dividing investigations into 3 

periods, 5 days of ad libitum water, 5 days of 

water deprivation, and 5 days of ad libitum water. 

Total body water, extracellular fluid, plasma, 

blood, and rumen volume were measured. 

Measurement of water turnover, weight change 

and body temperature were also made. Rumen 

normally contained 20% of body water. After 2 

days of deprivation, rumen fluid volume 

decreased by 56% and after 5 days decreased by 

80% and supplied 50% of the total water lost by 

bighorn sheep during dehydration. Bighorns were 

capable of surviving water loss equivalent to 20% 

of body mass after 5 days of water deprivation 

during summer. Almost 90% of water loss was 

extracellular fluid; plasma volume was decreased 

by 48% and interstitial volume by 20%. Normal 

interstitial and plasma fluid volumes increased 

during the summer and fall periods. Total body 

water did not increase, but fluid shifts from the 

intracellular fluid space accounted for the increase 

in extracellular fluid. Fecal water content was 

reduced to 4.1 g water kg-1 body mass day-1 after 5 

days of water deprivation. Urinary water loss was 

reduced to 1.5 g water kg-1 body mass day-1 at a 

concentration of 3.9 osm. Under normal 

conditions of water availability, Na was excreted 

in urine at levels below 30 meq L-1, K at 300 meq 

L-1. After water restriction, Na levels in urine 

increased to 170 meq L-1 and K to almost 1,000 

meq L-1. 

Turner, J. C. 1979. Osmotic fragility of desert bighorn 

sheep red blood cells. Comparative Biochemistry and 

Physiology 64A:167-175. 

Desert bighorn sheep (Ovis canadensis 

cremnobates) exposed to 5 days dehydration lost 

17 – 22% of their body mass, which they were 

capable of replacing within 1 hr after water was 

made available. Dehydrated bighorn tolerated a 

48% loss of their initial plasma volume. After less 

than 4 hr postrehydration, more than 50% of the 

lost plasma volume was replaced. The absorption 

of water from the postrehydration rumen occurred 

at moderate rate (1 – 2 L hr-1) with 13% of the 

initial postrehydration fluid volume absorbed 

during the first hr of rehydration. Within 9 hr 

postrehydration, less than 50% of the imbibed 

rumen volume remained. The osmotic fragility of 

the bighorns red blood cells improved with 

increased dehydration. Control values for 50% 

lysis in hyposmotic saline decreased from 77 mM 

NaCl to 68 mM NaCl after 5 days dehydration. 

Plasma concentration increased from 304 mOsm 

L-1 to 345 mOsm L-1 after dehydration and 

became regulated to control levels 4 hr 

postrehydration. Red blood cells osmotic 

concentrations remained constant at an average of 

252 mOsm L-1 during dehydration, rising to 279 

mOsm L-1 1 hr postrehydration and achieved 

control levels 5 hr post rehydration. 

Turner, J. C. 1984. Seasonal variation of red blood cell 

survival in desert bighorn sheep (Ovis canadensis 

cremnobates). Canadian Journal of Zoology 62:1227-

1231. 

The life span of red blood cells (RBCs) in captive 

and free-ranging desert bighorn sheep (Ovis 

canadensis cremnobates) was measured with 

[

32P]diisopropylfluorophosphate. The mean winter 

RBC life-span (156.6 days) was not significantly 

affected by season for captive animals maintained 

on a high nutritional plane and water, ad libitum. 

Free-ranging bighorn demonstrated a significant 
78 

difference between mean winter (155.9 days) and 

summer (209.9 days) RBC survival. Dehydration 

of captive bighorn significantly increased RBC 

survival, closely approximating that found in 

summer free-ranging animals. Desert bighorn 

RBCs exhibited a seasonal facultative response to 

the availability of water. Red blood cell life-span 

was significantly increased from 153.5 to 197.7 

days in animals experiencing extreme 

dehydration. The large spleen, relative to body 

mass, may accommodate extensive fluctuations in 

total RBC volume measured during dehydration 

and rehydration, preventing premature RBC 

degradation and an increased water requirement. 

Updike, D. 1977. Growth, energetics, and water 

balance of California mule deer fawns. M.S. thesis, 

California State University, Fresno, California, USA. 

44p. 

Growth, energetics, and water balance were 

assessed in California mule deer (Odocoileus 

hemionus californicus) fawns. Titrated water was 

used to determine water turnover rate. Mule deer 

fawns lost an average of 624 ml day-1 compared to 

a predicted value of 1,350 ml day-1 based on 

allometric calculations. The water turnover rate of 

California mule deer fawns was not significantly 

different than predicted based on its body mass, 

however it was at the lower end of the 95% 

confidence interval for mammals with similar 

body mass. 

Valtonen, M. H. 1980. Effects of dietary nitrogen and 

sodium chloride content on water intake and urine 

excretion in reindeer. Pages 274-277 in Reimers, E., E. 

Garre, and Skjenneberg, editors, Proceedings of the 

Second International Reindeer/caribou Symposium, 

Roros, Norway. 

The influence of nitrogen and NaCl load on water 

intake and urinary excretion was studied in 

reindeer (Rangifer tarandus) housed in 

temperature controlled stalls and fed low and high 

protein diets with and without a daily supplement 

of 10 g of salt. The effects of lichen diet were also 

studied. Increasing the dietary nitrogen resulted in 

a highly significant increase in water 

consumption, urine flow, and osmolality. 

However, even on high protein diet the urine 

osmolality was only 650 ± 97 mOsm kg-1 water 

(mean ± SD). The effect of supplementary salt on 

water intake was slight. Salt increased the urine 

osmolality on low protein diet, but on high protein 

diet it raised urine flow. Excretion rates of 

nitrogen, sodium, and potassium reflected the 

differences in dietary intake. On lichen diet with 

moisture content of 67% the reindeer did not drink 

any water. The urine osmolality was below that of 

plasma, but urea excretion remained the same low 

level as it did on the low protein diet. The surplus 

water is well excreted by reindeer kidney, but 

increased intake of dietary protein presupposes 

liberal water supply. 

Wesley, D. E. 1971. Energy and water flux in 

pronghorn. Ph.D. dissertation, Colorado State 

University, Fort Collins, Colorado, USA. 93p. 

Energy and water flux were studied in pronghorn 

(Antilocapra americana) using titrated water 

methods. Four trials conducted at 21 oC with 4 

female pronghorn aged 1 – 12 mo. showed that 

average body water decreased from 71.5 to 61.3% 

during this period. Water intake, flux, and 

turnover were higher for 1-month-old pronghorn 

than adult animals. Two-month-old pronghorn 

exposed to 32 oC significantly increased water 

intake, flux and turnover compared to exposure at 

21 oC. Energy metabolism trials conducted at 21 

oC with animals of 4 ages from 2-month to 18 

months indicated that 2-month-old animals 

showed higher energy intake, apparent digestible 

energy, and metabolizable energy (N corrected), 

energy retention, total heat production, and fasting 

metabolic rates than animals older than 7.5 

months of age. 

Wesley, D. E., K. L. Knox, and J. G. Nagy. 1970. 

Energy flux and water kinetics in young pronghorn 

antelope. Journal of Wildlife Management 34:908-912. 

Energy flow trials with 4 pronghorn (Antilocapra 

americana) ranging from 108 to 182 days of age, 

produced results similar to those described for 

other ruminants with the possible exceptions of 

total heat production and fasting metabolic rate. 

The comparatively high heat production may be 
79 

related to the higher metabolism of younger 

animals. Fasting metabolic rates were above the 

interspecies mean of 70 kcal kg0.75 day-1; similar 

results have occurred with other wild ruminants. 

Pronghorn, under the conditions tested, had a 

slightly higher content of body water than 

reported for other ruminants. This is feasible since 

pronghorn probably have a lower fat content than 

do most domestic or laboratory animals. Water 

flux in antelope is similar to that in domestic 

sheep and mule deer (Odocoileus hemionus). 

Noticeable differences existed between water 

kinetics of male and female pronghorn. 

Whisler, S. L. S. and S. L. Lindstedt. 1983. 

Physiological responses to water deprivation in 

pronghorn antelope. Journal of the Colorado-Wyoming 

Academy of Sciences 15:58 (Abstract). 

Pronghorn (Antilocapra americana) are found in 

arid and semi-arid precipitation zones in the 

western United States. As droughts are common 

in these regions, we hypothesized that pronghorn 

possess physiological water conserving 

mechanisms. We measured water loss parameters 

in pronghorn given ad libitum water intake and 

dehydrated pronghorn maintained at 15% weight 

loss. During dehydration, with evaporative water 

losses declining markedly, exhaled air 

temperature was lowered that alone would result 

in a 30% respiratory water savings. Basal 

respiratory rate decreased and panting during 

rumination ceased. During dehydration, food 

intake fell dramatically, lowering urine output. 

Urine urea nitrogen levels elevated slightly 

although total urine osmolality was constant 

(2,000 mOsm kg-1) regardless of hydration state. 

Also unchanged were plasma osmolality and 

hematocrit values. Fecal water loss fell to 10% of 

control values due to a smaller quantity of drier 

food. When faced with water shortage pronghorn 

lower their metabolic rate, thus reducing food 

intake, urine and fecal production, and oxygen 

consumption. This leads to reductions in urine, 

fecal, and evaporative water losses. Reductions in 

exhaled air temperature and fecal moisture also 

contribute to the drastic reduction in water 

turnover in dehydrated antelope. These 

physiological adaptations make pronghorn well 

suited to their dry environment. 

Williams, C. K. and B. Green. 1982. Ingestion rates and 

aspects of water, sodium, and energy metabolism in 

caged swamp buffalo, (Bubalus bubalis) from isotope 

dilution and material balances. Australian Journal of 

Zoology 30:779-790. 

In February 1976, 5 swamp buffalo (Bubalus

bubalis, 1 intact males and 4 steers) were placed 

into separate metabolism cages and fed Lucerne 

chaff, Lucerne pellets and water. Swamp buffalo 

were injected with 22Na in sodium chloride 

solution and titrated water to estimate food intake 

rate using turnover rates of 22Na and 3H. 

Exchanges in dry matter, sodium, water and 

energy were then measured. Tritium equilibrated 

in 6 hr and 22Na in 12 hr. The daily rate of water 

turnover was 34.7 ± 2.3 l, approximately 3 times 

that expected based on body size, reflecting an 

adaptation to tropical swamp habitat. Swamp 

buffalo had a high rate of inhibition, 30.8 ± 2.2 l 

day –1. Daily rates of water loss were partitioned 

as: fecal, 9.99 ± 0.76 l, urinary, 10.4 ± 0.76 l, 

pulmocutaneous, 14.3 ± 1.4 l. Swamp buffalo are 

not likely to be able to satisfy their daily water 

requirements from food alone during the dry 

season in Australia. Daily sodium turnover rate 

was 6.3 ± 0.4 mmol kg-1 W –1. Sodium levels in 

were low (8.3 ± 0.9 mmol kg –1). Apparent 

digestible energy (DE) intake per day for 

maintenance was 651 ± 41 kJ kg-1 W –1. Daily 

rates of evaporative heat loss were high, 481 ± 33 

kJ kg-1 W –0.75, exceeding the non-evaporative 

component of DE, 321 ± 35 kJ kg-1 W –0.75, 

evaporative processes may have contributed to the 

high maintenance DE. 

Williamson, D. T. and E. Delima. 1991. Water intake of 

Arabian gazelles. Journal of Arid Environments 21: 371-

378. 

The free water intake of 2 gazelle species, Gazella 

gazella and G. subgutturosa, was measured for a 

year, during which period shade temperatures 

ranged from a minimum of 1 oC to a maximum of 

49 oC. There was significant individual variation 

in water intake in both species. The relationship 

between temperature and mean water intake was 

non-linear and temperature explained 90 - 98% of 

the variance in mean daily water intake. No 

evidence was found for Arabian gazelles having 
80 

uniquely low water requirements and it was 

therefore inferred that their adaptation to aridity 

includes additional physiological and or 

behavioral mechanisms. The two species met their 

water requirement in different ways, but both 

responded to increased temperatures not only by 

drinking more but also by changing their diet to 

select for food with high moisture content. 

Wilson, A. D. 1970. Water economy and food intake of 

sheep when watered intermittently. Australian Journal 

of Agricultural Research 21:273-281. 

The water economy and food intake of mediumwool Merino, fine-wool Merino, and Border 

Leicester wethers were compared when water was 

made available only every 3 or 4 days. The 

comparisons were made on penned sheep with 2 

diets at both low (max. 12 oC) and high (max 36 

oC) temperatures. The Border Leicester used more 

water than the two groups of Merinos (20 – 40%), 

but they also ate more food per unit of body mass 

(15 – 18%). In proportion to food intake, the 

Border Leicesters and medium-wool Merinos 

drank 6 – 20% more water than fine-wool 

Merinos. It was concluded that although economy 

of water use may assist survival when water is 

unavailable, it appeared to be inversely related to 

food intake and therefore of limited value in 

selecting sheep for arid climates. The Border 

Leicesters lost more water in their feces than the 

Merinos, but similar amounts of water as urine. 

The volume of urine appeared to be related to the 

amounts of potassium and sodium excreted, since 

on the second to fourth day without water the 

concentration of potassium + sodium was 

maintained at 600 – 800 meq L-1 while the 

nitrogen concentration varied from 0.9 to 2.4 g 

100 ml-1. Nitrogen and potassium excretion in 

urine remained relatively constant, but sodium 

excretion varied from around 20meq day-1 on the 

first 1 – 2 days without water to 100 – 120 meq 

day-1 on the final 1 – 2 days. 

Wilson, A. D. 1974. Water consumption and water 

turnover of sheep grazing semi-arid pasture 

communities in New South Wales. Australian Journal of 

Agricultural Research 25:339-347. 

The water consumption and water turnover of 

Merino sheep grazing on 3 natural pastures of 

southwestern New South Wales, Australia were 

recorded throughout 1 year, and supplementary 

data on the water consumption of sheep on some 

pastures were collected for a further 2 - 4 years. 

On Danthonia caespitosa grassland, water was 

consumed for up to 7 months each year over the 

summer months. Maximum intakes were 3.0 - 3.5 

L/sheep/day, but this was reduced for 1-2 weeks 

after rain of less than 25 mm and for longer 

periods after heavier falls. The provision of shade 

reduced water turnover by a maximum of 0.3 - 0.5 

L day-1 on some occasions only, which indicates 

that shade, is of little importance to woolled 

sheep. On the saltbush (Atriplex vesicaria) and 

belah-rosewood (Casuarina cristata – 

Heterodendrum oleifolium) communities, water 

intakes were up to 6-7 L day-1 in summer. In the 

particularly dry summer of 1972 - 72, water 

intakes of the sheep on saltbush rose to 12 L day-1

for several months. The higher water intakes of 

these sheep were attributed mainly to the high 

mineral content of the Atriplex and Bassia spp. 

eaten by them, although the sheep on Danthonia, 

those on the bush communities consumed 

significant amounts of water throughout the 

winter in years of low rainfall. 

Wilson, R. T. 1989. Ecophysiology of the Camelidae 

and desert ruminants. Springer-Verlag, Berlin, 

Germany. 

This book provides a review of the climate, types, 

and locations of deserts of the world. 

Physiological mechanisms of camels, sheep, 

goats, oryx (Oryx beisa), eland (Taurotragus 

oryx), springbok (Antidorcas marsupialis), dorcas 

gazelle (Gazella dorcas), Grant’s gazelle (G. 

granti), Thomson’s gazelle (G. thomsonii), and 

Dik-dik (Rhynchotragus kirki) for 

thermoregulation, water balance, kidney function, 

and nutrition are reviewed. 

Wright, D. E. 1982. Applications of labeled water in 

animals nutrition and physiology. I. Measurement of 

individual intakes of grazing animals. Pages 69-76 in

Use of titrated water in studies of production and 
81 

adaptations in ruminants. International Atomic Energy 

Agency, Vienna, Austria. 

Methods for measuring individual animal intakes 

of food or liquid labeled with tritium or deuterium 

are reviewed. The errors associated with these 

techniques have been measured and the methods 

for estimating individual food, water, or milk 

intakes are discussed. 

Wright, D. E. 1982 Applications of labeled water in 

animal nutrition and physiology. II. Measurement of milk 

intake. Pages 77-88 in Use of titrated water in studies 

of production and adaptations in ruminants. 

International Atomic Energy Agency, Vienna, Austria. 

The application and validity of isotopic water to 

measure the milk intake of suckling lambs and 

calves are discussed. A method using 2 isotopes 

of iodine is described. Partitioning the intake of 

water in the offspring into that from milk and that 

from other sources, using double-labeled 

technique (tritium or deuterium) is also presented. 

Wright, D. E. 1982. Use of labeled water in studies on 

the nutrition and physiology of grazing ruminants in 

New Zealand. Pages 91-102 in Use of titrated water in 

studies of production and adaptations in ruminants. 

International Atomic Energy Agency, Vienna, Austria. 

Application of isotopic water in animal production 

studies of grazing ruminants in New Zealand is 

described. These include the seasonal and 

nutritional effects on water metabolism of dairy 

cattle and meat breeds of sheep, milk intakes of 

calves and lambs, and individual intakes of dietary 

supplements to control diseases. 

Woodall, P. F. and J. D. Skinner. 1993. Dimensions of 

the intestine, diet, and fecal water loss in some African 

antelope. Journal of Zoology 229:457-471. 

Measurements of the intestine of 16 species of 

antelope were allometrically analyzed. Moisture 

content of the digesta showed greatest 

interspecific variation in the spiral and distal 

colon. Small intestine length showed positive 

allometry, its circumference showed negative 

allometry, resulting in a surface area, which was 

isometric or related to metabolic rate. Dimensions 

of the villi were non-allometric. Grazers had 

lower surface areas of the small intestine than 

intermediates/concentrate selectors owing to 

smaller circumferences. In the large intestine, the 

dimensions of the distal colon showed the greatest 

interspecific variation. Lengths of the large 

intestine showed positive allometry except for the 

caecum, which was isometric. Circumferences 

and areas of the large intestine were isometric or 

related to metabolic rate. Species producing dry 

dung had larger lengths and areas of the large 

intestine but smaller circumferences of the 

proximal and spiral colon and showed greater 

drying of digesta per unit area than those 

producing wetter dung. Grazers had smaller 

lengths, circumferences, and areas of the large 

intestine than intermediates/concentrate selectors. 

Woodall, P. F., V. J. Wilson, and P. M. Johnson. 1999. 

Size and moisture content of fecal pellets of small 

African antelope and Australian macropods. African 

Journal of Ecology 37:471-474. 

The authors compare the fecal moisture content of 

eight species of small African antelope and 12 

species of Australian macropod representing 

species with habitats that range from arid to 

mesic. Antelope had fecal moisture contents 

between 50 – 58% and macropods had fecal 

moisture contents between 61 – 80%. All antelope 

species had similar fecal moisture contents, 

whereas macropod species from arid 

environments had lower fecal moisture contents 

than those from more mesic environments. 

Yagil, R. 1985. The desert camel: comparative 

physiological adaptation. Karger, New York, New York, 

USA. 

The overall physiology of the camel is described. 

Thermoregulation and metabolism, urea 

metabolism, respiration and acid base balance, 

cardiovascular system and plasma, endocrine 

system, lactation, and reproduction are reviewed. 
82 

Yagil, R. and G. M. Berlyne. 1976. Sodium and 

potassium metabolism in the dehydrated and 

rehydrated Bedouin camel. Journal of Applied 

Physiology 41:457-461. 

The effects of 10 days dehydration and rapid 

rehydration on the sodium and potassium 

metabolism in the one-humped camel were 

examined. The research was carried out during 2 

periods in the summer, a cool and hot period. In 

the hot period the effects of dehydration were 

found to be more severe. The potassium 

metabolism was more affected than that of the 

sodium. The concentrations of potassium in the 

urine declined while those of sodium increased. 

There were also marked changes in the filtered 

loads, excreted loads, and reabsorption of the two 

cations. Following rehydration significant changes 

in the cation metabolism were recorded within 15 

- 45 min. It is suggested that antidiuretic hormone 

and not aldosterone caused the changes in the 

two-cation metabolism. 

Yagil, R. and G. M. Berlyne. 1977. Glucose loading and 

dehydration in the camel. Journal of Applied Physiology 

42:690-693. 

Five female Bedouin camels were subjected to 

large infusions of glucose, both when water was 

readily available and following 10 days of water 

deprivation. When camels were hydrated the extra 

glucose was readily given off in the urine with 

only a slight increase in blood levels. Following 

dehydration, the blood glucose levels increased 

greatly while the urinary excretion was limited. 

Dehydration led to decreased blood insulin levels, 

while glucose infusion led to increased levels. The 

data showed that the acclimatization of the camel 

to dehydration is not only a question of long-term 

adaptation to desert conditions but that even 

following acute nonphysiological stress, i.e., 

glucosuria, excess loss of body water was 

prevented. 

Yagil, R. and G. M. Berlyne. 1977. Renal handling of 

creatine in various stages of hydration in the camel. 

Comparative Biochemistry and Physiology 56A:15-18. 

The renal creatine handling of camels was 

examined when the animals were hydrated, 

dehydrated, and rehydrated. A rise in the creatine 

and inulin clearance ratios was found following 

dehydration and a decrease following rehydration. 

When exposed to heat and also when dehydrated, 

the camels had gross changes in renal creatine 

handling with a tendency to tubular secretion. It is 

concluded that endogenous creatine 

determinations are no measure of glomerular 

filtration rate in the camel. 

Yagil, R. and G. M. Berlyne. 1978. Glomerular filtration 

rate and urine concentration in the dromedary camel in 

dehydration. Renal Physiology 1:104-112. 

The glomerular filtration rate, effective renal 

plasma flow, urine osmolality, urine flow rate, 

urea extraction, osmolar clearance, and free water 

reabsorption were measured in 5 female camels in 

control conditions and also after 10 days 

dehydration in both early and mid-summer. There 

was a loss of 23% in mean body mass and a fall of 

75% in glomerular filtration rate in severe 

dehydration, with a parallel reduction in the 

effective renal plasma flow and in urine flow rate. 

Urine osmolality reached a maximum of 1,466 

mOsm kg-1 in severe dehydration of mid-summer, 

the highest individual osmolality being 2,372 

mOsm kg-1. Osmolar clearance, free water 

absorption, and urinary urea excretion were lower 

in dehydration. Urea/inulin clearance ratio was 

significantly lower in dehydration. Sodium 

excretion did not change in dehydration. 

Fractional reabsorption of urea was higher in 

dehydration, reaching a maximum value of 74% 

of the filtered load. The fall in urinary urea 

concentration was one of the factors contributing 

to the poor concentrating ability of the severely 

dehydrated camel kidney, probably caused by the 

fall in glomerular filtration rate and increase in 

tubular reabsorption of urea, rather than by protein 

deprivation. 

Yagil, R., H. Amir, Y. Abu-Rabiya, and Z. Etzion. 1986. 

Dilution of milk: a physiological adaptation of mammals 

to water stress? Journal of Arid Environments 11:243-

247. 
83 

A study was carried out on the effect of 

dehydration on the milk water content of humans 

and cows. Milk from Bedouin women was 

examined in winter and in summer, when urine 

analysis confirmed that the mothers were lacking 

drinking water. The milk content of cows not 

getting enough to drink because of a mechanical 

fault in the watering system, was compared with 

cows getting water ad libitum. There was a 

dilution of the milk, in both partially dehydrated 

Bedouin women and the partially dehydrated 

cows. It is surmised that dilution of milk, when 

drinking water is scarce is a physiological 

phenomenon for the survival of the young in arid 

areas. It is postulated that there is an endocrine 

regulation system for the dilution of milk; the 

hormones governing milk secretion – prolactin – 

oxytocin – act like the hormones responsible for 

water homeostasis (ADH and aldosterone). Water 

is therefore withdrawn from the intestine and 

kidneys and secreted into the milk. 

Yagil, R., U. A. Sod-Moriah, and N. Meyerstein. 1974. 

Dehydration and camel blood I: red blood cell survival 

in the one-humped camel, Camelus dromedarius. 

American Journal of Physiology 226:298.300. 

Half-life and survival time of camel red blood 

cells were determined by labeling with 51Cr. The 

determinations were made on 3 separate 

occasions, the first in summer, and then in wither 

with water ad libitum followed by a summer of 

chronic dehydration. The shortest red blood cell 

survival time was recorded in winter, and the 

longest survival and half-life times were recorded 

under chronic dehydration n the summer. Normal 

summer determinations with water ad libitum 

were similar to those found in other ruminants. 

The lengthening of the red blood cell life span 

during dehydration may contribute to the ability 

of the camel to preserve water. 

Yagil, R., U. A. Sod-Moriah, and N. Meyerstein. 1974. 

Dehydration and camel blood II: shape, size, and 

concentration of red blood cells. American Journal of 

Physiology 226:301-304. 

This experiment examined the changes that occur 

in the red blood cells during hydration, 

dehydration, and intervals after rehydration. With 

dehydration the cell size diminishes but the shape 

does not change. These changes were confirmed 

in hypertonic saline solutions. Only in 20% saline 

solution was beveling of the membrane observed. 

After repaid rehydration the cells increased in 

size, as was found in hypotonic saline solutions. 

Hemolysis was observed in 0.2% saline. The 

hematocrit, number of cells, and hemoglobin 

content also changed during the various states of 

hydration. It is concluded that the red blood cell 

plays an important role in the ability of the camel 

to survive extreme environmental conditions. 

Yagil, R., U. A. Sod-Moriah, and N. Meyerstein. 1974. 

Dehydration and camel blood III: osmotic fragility, 

specific gravity, and osmolality. American Journal of 

Physiology 226:305-308. 

Camel blood was examined to determine whether 

dehydration and rapid rehydration affect the 

osmotic fragility of the red blood cells. The 

critical hemolytic volume, specific gravity, and 

osmolality were also determined. It was found that 

the red blood cells of the dehydrated camel are 

more resistant to hypotonic saline solutions than 

those of a hydrated camel. The fragility changes 

together with the state of hydration. Changes are 

also found in critical hemolytic volume, density, 

and osmolality. It is concluded that despite 

changes in the red blood cell, it remains functional 

in extreme environmental conditions. This fact 

contributes to the camel’s ability to withstand 

prolonged dehydration and rapid rehydration. 

Yagil, R. and Z. Etzion. 1979. The role of antidiuretic 

hormone and aldosterone in the dehydrated and 

rehydrated camel. Comparative Biochemistry and 

Physiology 63A:275-278. 

The role of antidiuretic hormone and aldosterone 

in the dehydrated and rehydrated camel was 

studied in 6 female camels maintained outdoors in 

pens. Aldosterone secretion was higher in 

normally watered camels in summer than in 

winter. Aldosterone and antidiuretic hormone 

secretion increased following dehydration. It is 

suggested that the antidiuretic hormone besides its 

water reabsorptive functions in the kidney, 
84 

initiates aldosterone secretion. The aldosterone 

then works primarily on the colon causing 

absorption of salt and water. When camels were 

rehydrated the aldosterone and antidiuretic 

hormone secretion diminished, but to prevent 

hemodilution great amounts of aldosterone were 

secreted 24 hr following drinking. 

Yagil, R. and Z. Etzion. 1980a. Effect of drought 

condition on the quality of camel milk. Journal of Dairy 

Research 47:159-166. 

Ten-day periods of water restriction flowed by 2 

hr ad libitum water caused changes in camel milk. 

The changes were different from those reported in 

other mammals. At the end of each dehydration 

period there were increased water percentages in 

the milk when compared with milk in hydrated 

camels. The content of fat, lactose, and protein 

declined. Concentrations of Na, K, phosphate, and 

chloride in milk increased while Ca and Mg 

concentration declined. The urea concentration of 

the milk was unchanged. The young suckling 

calves showed no signs of stress during the 

dehydration periods. It was concluded that the 

milk of dehydrated camels is an excellent human 

food in arid areas, as the water and salt content are 

high while the nutritive value remains good. 

Yagil, R. and Z. Etzion. 1980b. Milk yield of camels 

(Camelus dromedarius) in drought areas. Comparative 

Biochemistry and Physiology 67A:207-209. 

The milk yield was determined in camels in the 

heat of summer when drinking water was 

restricted to once per week for 2 hr. The amount 

of milk was determined by dilution of tritium in 

the calves. A steady amount of 6 L day-1 camel-1

was produced. The calves had no other source of 

water except their mother’s milk. It is concluded 

that the capability of the camel to produce milk of 

good composition and quantity for human 

consumption when water is severely restricted is 

of extreme importance. 

Yagil, R., Z. Etzion, and G. M. Berlyne. 1975. Acid-base 

parameters in the dehydrated camel. Tijdschrift voor 

Diergeneeskunde 100:1105-1108. 

The effect of prolonged (10 days) dehydration on 

acid-base parameters of camel was examined. The 

pH and PCO2 levels rose significantly in the 

course of dehydration. This state was comparable 

with compensated non-respiratory alkalosis found 

in other animals. The plasma sodium, and 

magnesium levels rose significantly also. The 

plasma oxygen and calcium levels declined 

significantly. There was no significant change in 

potassium and phosphate levels. It is concluded 

that the changes found in acid-base status 

following dehydration are further evidence of 

water preservation mechanisms in the dehydrated 

camel. 

Yagil, R., Z. Etzion, and J. Ganani. 1978. Camel thyroid 

metabolism: effect of season and dehydration. Journal 

of Applied Physiology 45:540-544. 

The thyroid function of normally hydrated and 

dehydrated camels was examined in winter, 

spring, and summer. The thyroid was stimulated 

in summer when water was available, but 

inhibited flowing dehydration. It is concluded that 

the decline in thyroid function, as gauged by 

hormone secretion during dehydration in the 

summer, aids in preservation of body water by 

decreasing pulmonary water loss and dropping 

basic metabolism. 

Yesberg, N. E., M. Henderson, and O. E. Budtz-Olsen. 

1973. Hydration and vasopressin effects on glomerular 

filtration rate in sheep. Australian Journal of 

Experimental Biology and Medical Science 51:191-197. 

Hydration of sheep has been shown to result in a 

diuresis, which is accompanied by a significant 

increase in glomerular filtration rate. Antidiuretic 

hormone has also been shown to cause an increase 

in glomerular filtration rate, observable only in 

those sheep where the initial glomerular filtration 

rate has not been raised by prior hydration. It is 

suggested that antidiuretic hormone has a two-fold 

effect on water excretion; an increase in water loss 

through its glomerular filtration rate-augmenting 

effect and a decrease in water loss through its 

ability to increase tubular water reabsorption. The 

diuretic effect of antidiuretic hormone frequently 

observed in non-hydrated sheep, where 
85 

glomerular filtration rate initially is low and 

tubular water reabsorption high, is probably due to 

a relatively large change in the former and a 

minor change in the latter of these two effects. 

Yousef, M. K., D. B. Dill, and M. G. Mayes. 1970. Shifts 

in body fluids during dehydration in the burro, Equus 

asinus. Journal of Applied Physiology 29:345-349. 

The mechanisms underlying the dehydration 

tolerance in the burro were studied. A study was 

conducted using 2 burros to partition body fluid 

compartments before and after dehydration. 

Dehydration for 48 hr including a 10-h walk 

reduced body mass about 18%. Intracellular fluid 

volume decreased from 77.9 to 82.9 L, 

extracellular fluid volume, from 53.2 to 45.8 L, 

and plasma volume, only from 9.0 to 8.4 L. The 

ability of the burro to conserve blood volume and 

presumably to maintain circulatory adequacy 

gives a likely explanation of its well being even 

after 20% dehydration. The difference in water 

loss between 2 nonexercising burros is found to be 

behavioral and partly related to the time spent in 

the sun. Rehydration was rapid and overhydration 

did not occur. Water content of dehydrated burros 

was similar to that of desert antelopes but greater 

than values reported on the camel. 

Zervanos, S. M. 2002. Renal structural adaptations 

among three species of peccary. Southwestern 

Naturalist 47:527-531. 

Several morphological characteristics of the 

kidney were studied to determine the degree of 

interspecific and intraspecific adaptation that 

might occur within 3 species of peccary from arid, 

semi-arid, and moist habitats. Paired kidney 

samples were collected from collared (Tayassu 

tajacu), Chacoan (Catagonus wagneri), and whitelipped (T. pecari) peccaries from habitats varying 

in water availability. Two indexes for renal 

concentrating ability, the relative medullary 

thickness and relative medullary area, exhibited 

higher values for animals from arid and semi-arid 

habitats than for those from moist habitats. 

Relative kidney mass also was higher for collared 

peccaries from dry environments. It was 

concluded that renal structures are flexible in 

response to environment variation, and the 

differences observed were related to the 

adaptability of renal concentrating structures. 

Zervanos, S. M. and G. I. Day. 1977. Water and energy 

requirements of captive and free-living collared 

peccaries. Journal of Wildlife Management 41:527-532. 

In 1974 – 1976, water and energy requirements of 

captive collared peccaries (Dicotyles tajacu) at the 

Phoenix Zoo, Phoenix, Arizona and free-living 

wild peccaries at the Three-bar Wildlife Area, 

Gila County, Arizona were studied. Titrated water 

was used to determine water turnover in both 

captive and free-living collared peccaries. 

Hydrated captive peccaries turned over 1.58 L of 

water day-1, whereas turnover rates for the 

dehydrated captive group were only 0.55 L day-1. 

Free-living peccaries under field conditions lost 

1.35 L water day-1 in summer and 1.17 L day-1 in 

winter. A seasonal determination of field energy 

requirements was made using the water loss value 

for free-living peccaries. To meet daily field 

energy requirements in summer a peccary ate 1.54 

kg (wet mass) of cactus, while in winter a peccary 

are 1.47 kg. The energy assimilated from this 

amount of cactus was determined to be 825.7 kcal 

day-1 and 897.5 kcal day-1, respectively. 

Zervanos, S. M. and J. A. Kauffman. 1981. Water and 

salt balance of free-ranging ponies on Assateague 

Island. Proceedings of the Pakistan Academy of 

Sciences 55:35-36. 

Field collections and observations were conducted 

to evaluate some of the physiological and 

ecological parameters affecting salt and water 

balance of free-ranging feral ponies inhabiting 

Assateague Island National Seashore, Maryland in 

June 1978 to July 1980. A total of 592 hours of 

direct field observation and sample collection was 

accumulated. The ponies' major avenue of water 

gain was in preformed water contained in the 

grasses consumed. This amounted to 65.5 ml kg-1 

day-1. The major avenue of water loss was 

evaporative with an estimated loss of 69.0 ml kg-1 

day-1. Total water balance amounted to 110.8 ml 

kg-1 day-1. It was calculated that the ponies 

consumed 288.8 mg kg-1 body mass of sodium 
86 

and 282.2 mg kg-1 Cl day-1 by grazing on marsh 

cord grass. The major avenue of loss of these ions 

was through urine production. Urine 

concentrations averaged 204.8 neq L-1 for sodium 

and 248.6 neq L-1 for Cl. Comparing these values 

with other equids indicates that the ponies have 

not acquired any special adaptation to conserve 

water, even with their high salt diets. 

Zervanos, S. M. and S. Naveh. 1988. Renal structural 

flexibility in response to environmental water stress in 

feral hogs. Journal of Experimental Zoology 247:285-

288. 

Several morphological characteristics of the 

kidney were studied at the Pennsylvania State 

University Swine Research Laboratory at 

University Park, Pennsylvania, to determine the 

degree of acclimatization that may occur in 3 

groups of feral hogs live-captured in different 

environments. Two groups of hogs were living in 

the wild, while another was raised in captivity for 

3 generations and was directly descended from 1 

of the wild-living groups. The 2 groups of wild 

hogs were living under 2 different types of water 

stress conditions. One group experienced periodic 

drought, and the other ate a high salt diet. The 

captive hogs were given food and water ad 

libitum. The captive-raised hogs had significantly 

lower relative medullary thickness (RMT) and 

relative medullary area (RMA) values (RMT of 

2.35; RMA of 0.35) than either group of hogs 

living in the wild (RMT of 2.70 and 2.69; RMA of 

0.41 and 0.44). Because the feral hogs living in 

the wild were exposed to a higher degree of water 

stress than the captive-raised hogs, it was 

concluded that the differences in observed kidney 

structure were due to acclimatization. 

Marsupial Mammals 

Barboza, P. S. 1993. Effects of restricted water intake 

on digestion, urea recycling and renal function in 

wombats (Marsupialia: vombatidae) from contrasting 

habitats. Australian Journal of Zoology 41:527-536. 

The effects of restricted water intake on digestion, 

urea recycling and renal function in wombats 

(Marsupialia: Vombatidae) from contrasting 

habitats. Responses to limited water availability 

were studied in two species of wombats from 

mesic (Vombatus ursinus) or xeric (Lasiorhinus 

latifrons) habitats. Four Vombatus and three 

Lasiorhinus were fed a low-quality straw-based 

diet containing 0.6% nitrogen and 68% neutral 

detergent fiber (dry-matter basis). Restriction to 

50% of ad libitum intakes of drinking water 

reduced dry-matter intakes by 30% but did not 

alter digestibilities of fiber or nitrogen. Nitrogen 

balances were negative and similar between 

species and water intakes. Urea pool size (14Curea) increased during water restriction but ureaentry rates and the proportion of urea recycled to 

the gut were similar between water intakes (78-

89%). Titrated water was given to wombats in 

single intramuscular or intraperitoneal doses. 

Times to equilibrium of tritium in urinary water 

were large and variable (45 ± 36 hr). Urinary 

tritium concentrations often declined erratically 

after equilibrium, and were 14 ± 14% lower than 

the tritium concentration in the blood. The 

irregular kinetics for titrated water suggest that the 

water-dilution method requires validation for the 

wombats. Urinary and fecal water losses were 

reduced by 60% during water restriction. Water 

was mainly lost in the feces, which were drier in 

Lasiorhinus (41% dry matter) than in Vombatus

(31%). As blood hematocrit and plasma 

osmolality were similar between water intakes, 

extracellular spaces were apparently maintained 

during water restriction. Glomerular filtration 

rates (creatinine clearance) were low (12 ml min-1) 

and similar between water intakes. Therefore, 

more concentrated urine was produced by tubular 

reabsorption in water-restricted wombats. 

Lasiorhinus had greater urinary osmolalities and 

urine: plasma rations of creatinine, which 

reflected a greater urine-concentrating ability than 

Vombatus. Apparent water intakes and the ability 

to reduce urinary and fecal water losses in the 

wombats are similar to those of kangaroos. The 

contrasting abilities of Vombatus and Lasiorhinus

to minimize both these water losses are directly 

related to their separate distributions. 

Blaney, C. E., T. J. Dawson, H. C. K. McCarron, R. 

Buffenstein, and A. K. Krockenberger. 2000. Water 

metabolism and renal function and structure in eastern 

grey kangaroos (Macropus giganteus): responses to 
87 

water deprivation. Australian Journal of Zoology 

48:335-345. 

The effect of water deprivation on water 

metabolism and renal function in eastern grey 

kangaroos (Macropus giganteus) were studied 

using titrated water and compared to those of the 

red kangaroo (M. rufus) which inhabits more arid 

habitats than the eastern grey kangaroo. Freeranging animals were captured so that blood could 

be drawn and titrated water injected then released. 

Indices of relative medullary thickness and 

medullary to cortical ratio, derived from kidney 

morphology are indicators of renal concentrating 

ability. In M. giganteus both of these values were 

lower than in M. rufus; 5.24 ± 0.15 (mean ± SE) 

for M. giganteus and 6.00 ± 0.10 for M. rufus.

Maximal measured urine concentrations were 

2,444 ± 59 (M. giganteus) and 3,135 ± 165 mOsm 

kg-1 (M. rufus), with individual concentrations 

being 2,752 and 4,054 mOsm kg-1. Kidney 

function in hydrated and dehydrated M. giganteus

was assessed via glomerular filtration rates, urine 

flow rate, and concentration index. As measured 

by these parameters, M. giganteus had renal 

water-conserving capacities similar to or superior 

to, those of many comparable-sized arid-zoneinhabiting placental mammals, but below those of 

M. rufus. Water metabolism, as measured by 

water turnover, showed a similar pattern. 

Bradshaw, S. D., K. D. Morris, and F. J Bradshaw. 

2001. Water and electrolyte homeostasis and kidney 

function of desert-dwelling marsupial wallabies in 

Western Australia. Journal of Comparative Physiology 

171B: 23-32. 

Prolonged drought, necessitating conservation of 

water, is one of the major environmental 

challenges faced by many Australian marsupials. 

Radioactive isotopes of water and sodium were 

used to assess the ability of 2 species of marsupial 

wallabies to maintain water and electrolyte 

balance during periods of extreme water 

deprivation in the arid Pilbara region of Western 

Australia in 1987 and 1988. The spectacled harewallaby, (Lagorchestes conspicillatus) has the 

lowest mass-specific rate of water turnover at 27.5 

ml kg-0.82 day-1 yet reported for any mammal and 

was 2 to 3 orders of magnitude lower than that of 

the Rothschild's rock-wallaby, (Petrogale 

rothsdchild). Studies of renal function show that 

the hare-wallaby conserves water by producing 

highly concentrated urine under the influence of 

lysine vasopressin (LVP), the anti-diuretic 

hormone in macropodid marsupials. In contrast, 

rock-wallabies show unusual renal responses to 

water deprivation, with no change in LVP levels 

and a limited response to water deprivation 

involving a reduction in renal plasma flow and 

glomerular filtration rate, with no significant 

change in tubular function. Both species are able 

to maintain water and electrolyte homeostasis 

during periods of drought, highlighting the 

efficacy of their differing adaptive solutions to the 

problem of water scarcity, although the harewallaby is superior to the rock-wallaby in this 

respect. Rock wallabies appear to rely primarily 

on behavioral rather than physiological responses 

for their survival in the Pilbara and appear to be 

more vulnerable to extinction in the event of 

significant habitat modification. The secure nature 

of their rock habitat, however, means that they 

have suffered less than hare-wallabies in the 

recent past. 

Buffenstein, R., H. C. K. McCarron, and T. J. Dawson. 

2001. Erythrocyte osmotic fragility of red (Macropus 

rufus) and grey (Macropus fuliginosus and Macropus 

giganteus) kangaroos and free-ranging sheep of the 

arid regions of Australia. Journal of Comparative 

Physiology 171B:41-47. 

The mean corpuscular fragility (MCF) of 

erythrocytes may reflect phylogenetic 

characteristics as well as an animal's ability to 

respond to the osmotic challenges associated with 

cyclic dehydration and rehydration. This type of 

ecophysiological stress is commonly encountered 

by animals living in arid regions and low MCF 

may contribute to their ability to survive and 

thrive in these xeric habitats. The eastern grey 

kangaroo has only in recent times extended its 

range into the arid zone, and is considered a more 

mesic inhabitant than the red kangaroo. We 

therefore compared the ability of eastern grey 

kangaroos and red kangaroos to handle prolonged 

periods of water restriction, as well as the MCF of 

the erythrocytes of free-ranging red, eastern grey 

and western grey kangaroos found at the Fowlers 
88 

Gap field station, New South Wales, Australia. In 

addition, the MCF of free ranging sheep 

inhabiting the same pastures were used as an 

experimental control; they are phylogenetically 

unrelated yet are subject to the same 

acclimatization stresses. While red kangaroos 

exhibited greater tolerance of dehydration 

compared to eastern grey kangaroos, the MCF of 

all 3 kangaroos species was similar and more 

resilient to osmotic stresses (MCF, 130 mOsm kg1

) than erythrocytes of sheep (MCF, 220 mOsm 

kg-1). The MCF did not change with water 

restriction, however, the erythrocytes of long-term 

captive populations fed a comparatively better 

quality diet were more resistant to osmotic shock 

than the free-ranging animals. Phylogenetic 

commonality rather than ecophysiological 

responses to life in the arid zone appeared to 

influence MCF. The MCF values of sheep 

corresponded to that of other ovines; similarly the 

MCF of kangaroos concurred regardless of their 

preferred habitats, ecological history and 

differential success in the arid zone. 

Dawson, T. J., M. J. S. Denny, E. M. Russell, and B. 

Ellis. 1975. Water usage and diet preferences of freeranging kangaroos, sheep, and feral goats in the 

Australian arid zone during summer. Journal of Zoology 

177:1-23. 

In much of the arid rangelands of Australia the 

common large mammalian herbivores are the 

native marsupials, the red kangaroo (Megaleia 

fufa) and the Euro (Macropus robustus), and the 

introduced eutherian species, the domestic sheep 

and the feral goat. In the north west of New South 

Wales a study was carried out to examine the 

patterns of water usage during summer of these 

species when they were free ranging in the same 

area. Drinking frequencies, water turnovers, 

electrolyte concentrations and diet preferences 

were determined and information on movements 

and dispersal from watering points. The 

marsupials had a much lower water usage than 

either of the eutherians. The titrated water 

turnover of the goats was three times and that of 

the sheep four times the value obtained for 

kangaroos. While much of the difference between 

the marsupials and eutherians appeared to be due 

to fundamental physiological differences the high 

water usage of sheep was in part related to the 

high intake of halophytic plants in their diets. The 

water turnovers of the red kangaroos and Euros 

were not found to be different. Drinking studies 

and urine osmolalities suggested, however, that 

the open plains-dwelling red kangaroos had a 

higher water requirement than the hill inhabiting 

Euro. The principle components of the diets of the 

red kangaroo were grasses; of the Euro, grasses 

and shrubs; of goats, trees and shrubs; of sheep 

halophytic shrubs. 

Denny, M. J. S. and T. J. Dawson. 1972. Water 

metabolism of kangaroos. Australian Mammalogy 1:66-

67 (Abstract). 

Studies on the total body water and water turnover 

in several species of macropodid are described 

using a method incorporating a radioactive 

hydrogen isotope to label the water molecule. The 

methods are described including the estimation of 

the equilibrium time for large kangaroos. Results 

of yard studies on 5 species of macropodid show 

that water turnover during winter is less than that 

found in eutherians and that the total body water 

values are generally higher. A description of a 

technique used to study water metabolism of 

kangaroos in the field is given. 

Denny, M. J. S. and T. J. Dawson. 1973. A field 

technique for studying water metabolism of large 

marsupials. Journal of Wildlife Management 37:574-

578. 

A study was undertaken on the euro (Macropus 

robustus), a large arid zone kangaroo to develop 

techniques for the investigation of the water 

metabolism of large free-living mammals. A twosample method using titrated water is described. 

This method requires the capture of an 

experimental animal at least twice over a period of 

2 weeks, but gives reliable values for total body 

water content and water turnover rates. 

Denny M. J. S. and T. J. Dawson. 1975. Effects of 

dehydration on body-water distribution in desert 

kangaroos. American Journal of Physiology 229:251-

254. 
89 

Thermoregulatory studies have been carried out 

on 2 species of desert kangaroos, the red 

kangaroo, (Megaleia rufa), and the euro or hill 

kangaroo, (Macropus robustus). These animals, 

like other marsupials, differ markedly from 

eutherian mammals in several aspects of 

temperature regulation. The basis of these 

differences is the lower metabolic rate of 

marsupials, the level of metabolism in marsupials 

being 30 – 35% below that of eutherians of 

similar size. At low air temperatures the 

kangaroos compensated for their low level of 

metabolism by having a high total body (core to 

fur tip) insulation. As expected from the 

environment in which they live both the red 

kangaroo and the euro have good 

thermoregulatory abilities at high ambient 

temperatures. The low level of metabolism may 

be advantageous under these conditions because 

less metabolic heat has to be dissipated by the 

evaporation of water. Panting appears to be a 

major avenue of evaporative heat loss in both 

species. However, preliminary studies suggest that 

sweating also may be important in the red 

kangaroo. A difference in the modes of 

evaporative heat loss would be consistent with the 

microhabitat selection of the two kangaroos. On 

hot summer days the red kangaroo is found 

residing in the sparse shade of small desert trees. 

The euros, however, are found around rocky 

outcrops in caves and under rock ledges. The 

greater reliance of the euro on respiratory water 

loss can be appreciated since in small caves air 

movement is low and humidity may be high. 

Freudenberger, D. O. and I. D. Hume. 1993. Effects of 

water restriction on digestive function in two 

macropodid marsupials from divergent habitats and the 

feral goat. Journal of Comparative Physiology 

163B:247-257. 

The effects of water restriction on digestive 

function in the euro (Macropus robustus 

erubescens) found in the arid zone of inland 

Australia, the eastern wallaroo (M.r. robustus) 

from more mesic regions of the eastern Australia, 

and the feral goat found throughout the range of 

M. robustus, were compared to examine some 

physiological adaptations required by herbivores 

for the exploitation of arid environments. Eight 

animals of each species were held in individual 

metabolism cages in temperature-moderated 

rooms and given a chopped hay diet ad libitum. 

Half the animals were restricted to 40 ml water kg0.80 day-1. This was 40%, 32%, and 57% of 

voluntary drinking water intake in the euro, 

wallaroo and goat, respectively. All species 

responded to water restriction by reducing fecal, 

urinary and evaporative water losses in 

association with reductions in feed intake. All 

animals increased urine osmolality and electrolyte 

concentrations but not to maximal levels, while 

packed-cell volume and plasma osmolality and 

electrolyte concentrations were unaffected by 

water restriction. The euro displayed a suite of 

characteristics that separated it from the wallaroo 

in terms of physiological adaptation, including 

lower voluntary water intake, an increase in fiber 

digestibility and maintenance of nitrogen balance 

during water restriction, and lower fecal water 

efflux associated with a consistently lower fecal 

water content (54% versus 59% water in the 

wallaroo during water restriction, P < 0.05). The 

euro's colon was 37% longer (P < 0.01) than that 

of the wallaroo. The goat had the lowest fecal 

water efflux (P < 0.05) and the longest colon (P < 

0.001). Water restriction did not affect water 

content in digesta, nor short-chain fatty acid 

concentrations or production rates in vitro. Total 

body water, as a proportion of body mass, was 

depressed (P< 0.05) in the macropodids, but not in 

the goat. The reduction in dietary nitrogen intake, 

which accompanied water restriction, was 

partially compensated by an increase in urea 

degradation in the gut from 68% to 76% of urea 

synthesis water-restricted macropodids. These 

responses to water restriction are discusses in 

relation to those reported in other macropodid and 

ruminant species. 

Hume, I. D. 1982. Water metabolism in Australian 

marsupials. Pages 195-206 in Use of titrated water in 

studies of production and adaptations in ruminants. 

International Atomic Energy Agency, Vienna, Austria. 

Several studies are discussed in which titrated 

water has been used to investigate water 

metabolism in Australian marsupials, particularly 

arid-zone species. Equilibration of injected titrated 

water in large kangaroos was slower than in 
90 

smaller marsupials and similar to that in 

ruminants and camels, presumably because of the 

high gut water space of all large forestomach 

fermenters. Loss of titrated water in urine, and 

insensible water during equilibration was also 

similar to that in ruminants. Total body water was 

similar whether estimated by equilibration or 

extrapolation. Total body water of small 

marsupial species (16 g to 6.5 kg body mass) was 

usually in the range found for small eutherian 

mammals (56 to 68% of body mass). However, in 

the larger kangaroos total body water ranged from 

73 to 78% of body mass, possibly due to the low 

body fat content and the high ratio of gut contents 

to total body mass of kangaroos. In general, the 

water turnover rate of marsupials is about 30% 

below that of eutherians; this has been related to 

their lower metabolic rate. Nevertheless, 

significant differences in water turnover have 

been found between some species. It has been 

suggested that there may be a correlation between 

water turnover rates measured under ad libitum 

water availability and the aridity of the animal’s 

habitat. However, this is not always so; 

differences in behavior and in the water content of 

the natural diet explain why some marsupials with 

high ad libitum water turnovers can survive in 

desert environments. The physiological state of 

the animals (e.g., lactation) has also been shown 

to affect water turnover, both in the laboratory and 

in the field. 

Kennedy, P. M. and G. E. Heinsohn. 1974. Water 

metabolism of two marsupials--the brush-tailed 

possum, Trichosurus vulpecula and the rock-wallaby, 

Petrogale inornata in the wild. Comparative 

Biochemistry and Physiology 47A:829-834. 

Water metabolism of the brush-tailed possum 

(Trichosurus vulpecula) and the rock-wallaby 

(Petrogale inornata) in the free-living, wild 

animals captured from 1970 – 1972 in the Hervey 

Range, Australia was studied using titrated water. 

The water turnovers of wild brush-tailed possums 

and plain rock-wallabies living in the same 

environment were determined at intervals 

throughout 2 years. The water turnover of nonlactating animals of both species did not vary 

significantly with season and averaged 89.3 ml kg1 day-1 for the possums and 80.7 ml kg-1 day-1 for 

the rock-wallabies. Lactating females had an 

increased water turnover and higher titrated water 

space than non-lactating animals. The daily water 

turnover of rock-wallabies in cages was 112 ml 

kg-1 in the presence of drinking water, and 80.8 ml 

kg-1 without drinking water. 

McCarron, H. C. K., R. Buffenstein, F. D. Fanning, T. J. 

Dawson. 2001. Free-ranging heart rate, body 

temperature and energy metabolism in eastern grey 

kangaroos (Macropus giganteus) and red kangaroos 

(Macropus rufus) in the arid regions of south east 

Australia. Journal of Comparative Physiology 171B: 

401-411. 

Eastern grey kangaroos (Macropus giganteus) are 

generally regarded as mesic inhabitants. Even 

though access to drinking water in permanent 

stock watering troughs is commonly available, 

these animals are still found in only low densities 

in arid pastoral areas. We hypothesized that the 

differential success of red (Macropus rufus) and 

grey kangaroos in the arid zone may be due to 

higher energy requirements of M. giganteus with a 

concomitant need for increased food rather than 

limitations imposed by inadequate water access. 

We test this by indirectly measuring energy 

expenditure through the monitoring of heart rate 

by radiotelemetry in semi-free ranging eastern 

grey and red kangaroos at the University of New 

South Wales arid zone research station at Fowlers 

Gap, New South Wales, Australia. Radiotelemetry 

measurements of heart rate were calibrated against 

oxygen consumption of animals maintained in an 

8-ha enclosure in the arid zone of southeast 

Australia. Heart rate provided a reliable estimate 

of oxygen consumption. This well-correlated 

relationship was curvilinear and was established 

for each individual. Behavioral observations 

revealed that both kangaroo species spent most of 

the day in low energy demanding activities. M. 

rufus were most active at night while M. 

giganteus were more active in the early mornings 

and late afternoons. Like other marsupials, both 

species had low field metabolic rates (FMRs). 

However, M. giganteus in keeping with their 

mesic history had higher FMRs than the more 

arid-adapted M. rufus, particularly during water 

restriction. Body temperature telemeters revealed 

a further species difference in that under hot 
91 

conditions when water is freely available, M. 

rufus exhibits a higher and more labile daytime 

body temperature than M. giganteus. During the 

hottest part of the day M. giganteus maintain body 

temperature, relying upon increased evaporative 

cooling mechanisms, such as licking. Indeed, only 

when access to drinking water was restricted was 

thermolability evident in M. giganteus. 

Differences in behavior and concomitant energy 

expenditure may thus contribute substantially to 

the divergent distribution and abundance of the 2 

kangaroo species. 

Nagy, K. A., C. Meienberger, S. D. Bradshaw, and R. 

D. Wooller. 1995. Field metabolic rate of a small 

marsupial mammal, the honey possum (Tarsipes 

rostratus). Journal of Mammalogy 76:862-866. 

Doubly-labeled-water measurements of field 

metabolic rates and water influx rates in freeranging honey possums (mean mass = 9.9 g) 

during late winter of 1986 in Western Australia 

indicated that these nectarivores had lower daily 

energy expenditures than did insectivorous, 

dasyurid marsupials of similar body mass. Honey 

possums are capable of using torpor, and some 

individuals apparently did so during this study. 

Honey possums have an unusually high basal 

metabolic rate, and their field metabolic rate is ca. 

2.7 times the basal rate, which is much lower than 

the 4.6 - 4.9 times the basal rate in small 

insectivorous marsupials. Nevertheless, the daily 

cost of living we measured for honey possums is 

75% greater than for eutherian mammals of 

similar body mass. Small marsupials in general 

have much higher energy and food requirements 

in the field than do small eutherian mammals. 

Nagy, K. A. and G. C. Suckling. 1985. Field energetics 

and water balance of sugar gliders, Petaurus breviceps

(Marsupialia: Petauridae). Australian Journal of Zoology 

33:683-691. 

Field energetics and water balance of sugar 

gliders (Petaurus breviceps) were studied near 

South Gippsland, Australia. Doubly labeled water 

measurements in free-ranging sugar gliders (121 

g) indicated that field metabolic rates (FMRs) 

averaged 62.5 L CO2 kg-1 day-1, which is 

equivalent to 169 kJ animal-1 day-1 (3.8 times basal 

metabolic rate). The females, most of which had 

small pouch young, weighed significantly less 

than males (112 v. 135 g), but mass specific 

FMRs did not differ significantly between sexes. 

Rates of water influx (mass-specific) also did not 

differ between sexes, and averaged 208 

ml/kg/day. The diet consisted of about two-thirds 

acacia gum, one-third mixed arthropods, and 

traces of bark (on a dry mass basis). Percentage 

apparent assimilation of dietary substances was 

88% for dry matter, 89% for energy, 86% for 

nitrogen and 61% for water. Gliders consumed 

11.2 g dry matter of food per animal each day. 

The diet contained 44% water (fresh mass basis), 

and provided about half of the water gliders 

obtained. The other half presumably was ingested 

as rainwater. In comparison with the ecologically 

similar Leadbeater's possums (129 g), sugar 

gliders had much lower metabolic rates while 

active outside their nests (17.4 v. 31.4 kJ hr-1 for 

possums), primarily because possums spent 

energy for activity 2.5 times faster than did sugar 

gliders. This suggests that gliding affords sugar 

gliders a considerable energetic saving, but 

portion of time abroad spent foraging and resting, 

and distribution, abundance and predictability of 

food resources may also account for this 

difference. 

Nagy, K. A., R. S. Seymour, A. K. Lee, and R. 

Braithwaite. 1978. Energy and water budgets in freeliving (Antechinus stuartii) (Marsupialia: Dasyuridae). 

Journal of Mammalogy 59:60-68. 

Rates of water flux and CO2 production were 

measured in the Brown Antechinus (Antechinus 

stuartii) in the field in 1974 - 1975 near 

Healsuilie, Australia, using doubly labeled water. 

Itemized dry matter, energy, and water budgets 

were determined for captive animals, and were 

used to estimate feeding rate and energy and water 

fluxes in free-living animals. In winter, steady 

state, field A. stuartii ingested 807 kcal kg-1 day-1

and metabolized 670 kcal kg-1 day-1. They 

consumed about 60% of their body mass in 

arthropods each day. There were no significant 

differences between metabolic rates of 

nonbreeding adult (July) males and females and 

breeding (August) females; satisfactory data for 
92 

breeding males were not obtained. Energy 

expenditures of A. stuartii were similar to those of 

several free-living, small eutherians, after 

accounting for differences in ambient temperature 

and body size. However, this comparison is 

complicated by the use of burrows and occurrence 

of torpor in some of these mammals. The 

energetic impact of A. stuartii in temperate 

evergreen forest lies between 60 and 370 kcal kg-1 

day-1. These rates are similar to those obtained for 

small eutherian insectivores in other communities. 

Water fluxes did not differ between males and 

females in the field, but mean flux rate in steadystate, adult A. stuartii in August (734 ml kg-1 day1

) was higher than in July (539 ml kg-1 day-1), 

apparently because they ingested rain water that 

fell abundantly in August. Laboratory results 

indicate that field animals obtain much more 

water than they need to maintain water balance. 

Nagy, K. A., S. D. Bradshaw, and B. T. Clay. 1991. 

Field metabolic rate, water flux, and food requirements 

of short-nosed bandicoots, Isoodon obesulus

(Marsupialia: Peramelidae). Australian Journal of 

Zoology 39:299-305. 

Field metabolic rates (FMRs) and water influx 

rates of free-living short-nosed bandicoots 

(Isoodon obesulus) were measured via the doubly 

labeled water technique on the Harry Waring 

Marsupial Reserve, Australia, from 14 - 20 April 

1980. Bandicoots ranging in body mass from 775 

to 1,825 g (mean = 1,230 g) had FMRs averaging 

0.908 ml CO2 g-1 hr-1, or 644 kJ day. This is about 

2.7 times predicted basal metabolic rate. Water 

influx rates during the summer measurement 

period were comparatively low, averaging 88.8 ml 

kg-1 day-1, or 103 ml day-1 for a 1,230 g animal. 

Feeding rate (dry matter intake) was estimated to 

be 45 g day-1, assuming that the food was half 

invertebrates and half plant tissues (dry matter 

intake). Preformed and metabolically produced 

water from the food can completely account for 

total water intake, indicating that bandicoots did 

not drink the rainwater or pond water that was 

available. The study population (estimated density 

= 0.63 bandicoots/ha) consumed food at a rate of 

about 62 g fresh matter ha-1 day-1 (equivalent to 27 

g dry matter or 605 kJ ha-1 day-1), which is similar 

to the food requirements of populations of small 

eutherian and marsupial insectivores in other 

habitats. 

Small Eutherian Mammals 

Alkon, P. U., A. A. Degen, A. Cohen, and H. Pollak. 

1986. Seasonal energy requirements and water intakes 

of Indian crested porcupine (Hystrix indica) in captivity. 

Journal of Mammalogy 67:333-342. 

Four adult male Indian Crested Porcupines 

(Hystrix indica), held in covered outdoor 

enclosures in the Negev Desert, Israel during the 

summer 1981 and winter 1982, were offered ad 

libitum water and a dry rodent ration (16.5% 

protein; 9% fiber; 19.2 kJ g-1 dry matter) at four 

nutritional planes (100%, 80%, 60%, and 49% of 

ad libitum intake) during consecutive 10-day 

feeding trials in summer (July - August) and 

winter (January - February). Water intakes were 

significantly higher in summer (137 ± 60 ml kg-1 

day-1; mean ± SD) than winter (53 ± 7 ml kg-1 day1

). There were no seasonal differences in ad 

libitum food intake, in dry matter digestibility 

(annual mean = 76.5%), or in gross energy 

digestibility (80.9%). Moreover, maintenance 

energy requirements (estimated from body mass 

changes) were similar in both seasons, and 

averaged 220 kJ kg-1 day-1. These results, 

supported by limited data from free-ranging H. 

indica, indicate that Hystrix porcupines are 

capable of substantial formation and mobilization 

of fat reserves. This is a useful adaptation in 

seasonally fluctuating arid environments. Large 

inverse changes in the proportional composition 

of body water and body solids are likely such that 

body mass is an inadequate index to body 

condition. 

Arad, Z. and C. Korine. 1993. Effect of water restriction 

on energy and water balance and osmoregulation of the 

fruit bat (Rousettus aegyptiacus). Journal of 

Comparative Physiology 163B:401-405. 

The energy, water balance, and osmoregulation of 

the fruit bat (Rousettus aegyptiacus) were studied 

during normal hydration and during water 

restriction (oven-dried apple diet) in the 

laboratory at the Israel Institute of Technology, 
93 

Haifa, Israel. The water input and output were 

balanced during both normal hydration and water 

restriction. The kidney of the fruit bat is well 

adapted to handle the water load from its fruit diet 

by excreting large volumes (14% of the body 

mass per day) of dilute urine (113 ± 25 mOsm kg1

 water) as well as reducing urine volume (-95%) 

and increasing urine concentration (555 ± 280 

mOsm kg-1 water) during water restriction. The 

hemocrit, plasma hemoglobin, and total protein 

concentrations did not increase during water 

restriction and heat exposure, suggesting the 

conservation of plasma volume. Gross energy 

intake was not affected by water restriction. 

However, digested energy intake and digestibility 

were significantly reduced. The effective 

regulation of energy and water budgets during 

water restriction suggests that the fruit bat can 

cope with seasonal climatic changes and with 

variable fruit supply during various seasons. 

Baverstock, P. R. and C. H. S. Watts. 1975. Water 

balance of small lactating rodents--I. ad libitum water 

intakes and effects of water restriction on growth of 

young. Comparative Biochemistry and Physiology 

50A:819-825. 

Ad libitum water consumption of lactating and 

non-lactating females of the xeric-adapted rodents 

(Notomys alexis, N. cervinus, N. mitchellii, 

Pseudomys australis, and Mus musculus) was 

studied in the laboratory. The increase in ad 

libitum water consumption during lactation was 

surprisingly small, particularly at small litter sizes. 

The effects of restricting the water intake of the 

lactating female on growth of the young were 

studied in N. alexis and M. musculus. In both 

species, lactation was sustained during water 

restriction but at reduced levels. The young were 

able to survive the reduced milk intake, but grew 

at a depressed rate. 

Baverstock, P. R., L. Spencer, and C. Pollard. 1976. 

Water balance of small lactating rodents--II. 

Concentration and composition of milk of females on ad 

libitum and restricted water intakes. Comparative 

Biochemistry and Physiology 53A:47-52. 

The concentration and composition of the milk of 

lactating rodents (Notomys alexis, N. mitchellii, N. 

cervinus, Pseudomys australis, and Mus 

musculus) on ad libitum and restricted water 

intakes was determined. Australian desert mice 

and laboratory house mice produced milk at 

concentrations above the average eutherian level. 

The major solid constituent of milk in all species 

was fat. During lactation, percent fat increased, 

but sugar and protein did not change. Water 

restriction tends to increase solid concentration in 

N. cervinus, P. australis, and M. musculus, with 

the increase being entirely due to fat. Milk 

concentration does not appear to be important in 

the water-balance of lactation of Australian desert 

rodents. 

Bell, G. P., G. A. Bartholomew, and K. A. Nagy. 1986. 

The roles of energetics, water economy, foraging 

behavior, and geothermal refugia in the distribution of 

the bat, Macrotus californicus. Journal of Comparative 

Physiology 156B:441-450. 

Energy metabolism, thermoregulation, and water 

flux of (Macrotus californicus) the most northerly 

representative of the Phyllostomidae, were studied 

in 1983 - 1984 in the laboratory at the University 

of California, Los Angeles, using standard 

methods, and energy metabolism and water fluxes 

were studied in the field using the doubly labeled 

water method together with a time budget. Daily 

energy expenditures of free-living bats averaged 

22.8 kJ during the winter study period. 

Approximately 60% of this was allocated to 

resting metabolism costs while in the primary 

roosts (22hr day-1). Macrotus californicus is 

unable to use torpor. The thermoneutral zone 

(TNZ) in this species is narrow (33 to 40 oC) and 

metabolic rate increased rapidly as ambient 

temperature decreased below the TNZ. Basal 

metabolic rate was 1.25 ml O2 g-1 hr-1, or 24 J g-1 

hr-1. Total thermal conductance below the TNZ 

was 1.8 mW g-1 oC, similar to values measured for 

other bats. Evaporative water loss showed a 

hyperbolic increase with increasing ambient 

temperature, and was approximately 1% of total 

body mass hr-1 in the TNZ. The success of these 

bats as year round residents in the deserts in the 

southwestern United States is probably not due to 

special physiological adaptations, but to roosting 
94 

and foraging behavior. They use geothermallyheated winter roost sites (stable year-round 

temperatures of approximately 29 oC), which 

minimize energy expenditures, and they have an 

energetically frugal pattern of foraging that relies 

on visual prey location. These seem to be the two 

major factors that have allowed M. californicus to 

invade the temperate zone. 

Bintz, G. L. and W. W. Macken. 1980. The effect of 

water availability on tissue catabolism during starvation 

in Richardson’s ground squirrels. Comparative 

Biochemistry and Physiology 65A:181-186. 

Richardson’s ground squirrels were starved for 6 

days with no water or with limited water to 

compare the effect of these stresses on nitrogen 

catabolism and excretion. Starved ground 

squirrels fed 5.0 g of celery daily for five days 

catabolized 16% of the carcass mass, whereas 

starved ground squirrels with no water catabolized 

25% of the carcass mass and excreted 57% more 

nitrogen in the urine. The availability of water had 

a protein sparing effect during starvation, despite 

the fact that animals of both groups derived more 

than four-fifths of their energy requirements from 

adipose tissue. Ground squirrels did not appear to 

retain large amounts of catabolized nitrogen 

during starvation to reduce urinary water loss. 

Buffenstein, R. 1985. The effect of a high fiber diet on 

energy and water balance in two Namib Desert rodents. 

Journal of Comparative Physiology 155B:211-218. 

The effect of dietary fiber content on food 

consumption, digestive ability, and water balance 

was studied in the rock rat (Aethomys 

namaquensis) and pygmy gerbil (Gerbillurus 

paeba) in the Namibian Desert. In addition 

changes in these factors were monitored when 

water was withheld. Daily energy expenditure 

(DEE) for A. namaquensis remained fairly 

constant and similar to that predicted by mass 

despite changes in food and water regimes. The 

DEE of G. paeba was more variable. On a millet 

(low-fiber) diet with ad libitum water DEE was 

35% higher than the expected value. This 

increased still further within the first week of 

water deprivation before dropping back to prewater deprivational levels once mass had 

stabilized. On the high fiber diet, the DEE of G. 

paeba was similar to that predicted by mass when 

water was freely available. This was reduced by 

half when the animals were water stressed, 

suggesting that G. paeba might employ torpor 

under these circumstances. Water balance was 

assessed by measuring water intake and loss. 

Fecal water content when maintained on a millet 

diet was similar in both species, irrespective of 

whether water was freely available or withheld. 

However, urine concentrations and estimated 

evaporative water losses were higher in G. paeba. 

Observed differences in water loss are largely a 

function of variables related to weight specific 

metabolic rate. Differential water losses were 

offset by differences in metabolic water 

production, enabling both species to attain a 

positive water balance and survive indefinitely on 

a millet diet. When provided with a more fibrous 

diet, low assimilation efficiency and the resulting 

increase in fecal production, coupled with 

increased fecal water content, increased fecal 

water loss to such an extent that it precluded the 

maintenance of a positive water balance in either 

species. Despite increased urine concentration and 

a decline in evaporative water loss, both species 

rapidly succumbed to chronic water deprivation. 

Chevalier, C. D. 1989. Field energetics and water 

balance of desert-dwelling ringtail cats, Bassariscus 

astutus (Carnivora: procyonidae). American Zoologist 

29:8A. 

Field metabolic rates (FMR), water flux rates 

(WFR), and total body water (TBW) were 

estimated using doubly labeled water (tritium and 

oxygen-18) for non-reproductive, adult ringtail 

cats during late summer in the Sonoran Desert, 

central Arizona. Male and female ringtail cats 

differed in mass (males 838.1g, SE = 11.919; 

females, 656.3 g, SE = 22.844; P = 0.02) and in 

TBW:Mb ratio (males 0.697, SE = 0.025; females 

0.781 g, SE 0= 0.006, P = 0.02; combined: .739 g, 

SE = 0.020). No other differences between sexes 

were detectable, and no character scaled with 

mass. The data for sexes were combined for 

further analyses. Field metabolic rates averaged 

19.49 (SE = 1.278) L CO2 day-1 (approximately 

472 kJ day-1). This value approximated 81% of 
95 

predicted FMR for desert eutherians, and 2.69 

times minimum resting metabolism. Ringtail cats 

experienced no significant mass change and water 

intake, which was only slightly greater than water 

loss was 141% of predicted field WFR for desert 

eutherians and 153% of predicted standard WFR 

for arid-dwelling mammals. 

Culebras, J. M., G. F. Fitzpatrick, M. F. Brennan, C. M. 

Boyden, and F. D. Moore. 1977. Total body water and 

the exchangeable hydrogen II. A review of comparative 

data from animals based on isotope dilution and 

desiccation, with a report of new data from the rat. 

American Journal of Physiology 232:R60-65. 

Total body water determined by tritium space 

could be factitiously elevated by exchangeable H+

contained within water-soluble chemical 

configurations. Should this nonaqueous 

exchangeable H+

 total body water measurement 

by titrated water dilution would display a 

systematic upward and nonrandom error. Total 

body water was measured by titrated water 

dilution and subsequently by total body 

desiccation in 21 rats (Rattus norvegicus). Total 

body water was 71.4 ± 2.4% by titrated water 

dilution and 70.2 ± 1.5% by body desiccation. 

Analysis of variance of total body water vs. body 

weight showed a highly significant correlation 

both with desiccation and dilution. Covariance 

analysis of both methods showed no difference in 

slope. There was a difference in variance and 

means. Tritium space is 1.2% of body mass larger 

than total body water measured by desiccation. 

Total body water measured by titrated water 

dilution is accurate to within < 2% error. 

Deavers, D. R. and J. W. Hudson. 1979. Water 

metabolism and estimated field water budgets in two 

rodents (Clethrionomys gapperi and Peromyscus 

leucopus) and an insectivore (Blarina brevicauda) 

inhabiting the same mesic environment. Physiological 

Zoology 52:37-152. 

Water metabolism and field water budgets were 

estimated in 2 rodents (Clethrionomys gapperi

and Peromyscus leucopus) and an insectivore 

(Blarina brevicauda) captured in Tompkins 

County, New York. At an ambient temperature of 

20 oC shrews and voles lose water at about twice 

the rate predicted from body mass, while the 

white-footed mouse loses about one-third more 

water per day than predicted. Cold exposure (5 

oC) caused significant increases in water loss in 

the three species, and this increase was due to 

increased fecal and urinary losses while 

evaporative loss was not significantly changed; 

during cold exposure P. leucopus lost much less 

water than shrews and voles. When drinking water 

was reduced to the minimum requirements at both 

5 oC and 20 oC, the three species showed marked 

reductions in urinary, fecal, and evaporative 

losses. Minimum water requirements of P. 

leucopus were much lower than those of shrews or 

voles. On minimum water regimes urine 

concentration was significantly higher in P. 

leucopus (2,953 mOsm L-1) than in shrews (1,802 

mOsm L-1) or voles (1,758 mOsm L-1), and ability 

to concentrate urine in these three as well as 

numerous other mammals correlated well with 

relative medullary thickness of the kidneys. Water 

budgets for the three species were calculated 

based on energy requirements; the protein, salt 

and water intake resulting from feeding and 

obligatory water loss. These calculations revealed: 

(1) shrews and voles, despite their high water 

requirements, are in effect forced to consume 

large quantities of low-caloric and high watercontent food with consequent intake of large 

quantities of preformed water and probably 

remain in water balance throughout the year; (2) 

P. leucopus may need to supplement their diet 

with small amounts of drinking water in the 

winter, but their summer diet probably supplies 

sufficient water. 

Degen A A. 1997. Ecophysiology of Small Desert 

Mammals. Springer-Verlag, Berlin, Germany, 296p. 

This book reviews the ecophysiology of small 

desert mammals including issues related to body 

size and allometry, heat transfer and body 

temperature, behavioral adaptations, water 

requirements and water balance, energy 

requirements and energy flux, and reproduction 
96 

Degen, A. A. and M. Kam. 1992. Water intake in two 

coexisting desert rodents, Acomys cahirinus and 

Gerbillus dasyurus. Journal of Mammalogy 73:201-206. 

The common spiny mouse (Acomys cahirinus) 

and Wagner's gerbil (Gerbillus dasyurus), are 

omnivorous Old World rodents that coexist in 

rocky habitats in the deserts of Israel. They differ 

in their diets in that A. cahirinus consumes 

proportionately more snails and animal matter 

than G. dasyurus and G. dasyurus consumes 

proportionately more seeds than A. cahirinus. 

Rodents were offered seeds and either water ad 

libitum, ca. 50% of ad libitum. Total water intake, 

or denied water. Both species were able to 

maintain steady state body mass on both ad 

libitum and 50% ad libitum water. Furthermore, 

both species lost body mass when denied water. 

However, the daily rate of loss of body mass of G. 

dasyurus was slower than that of A. cahirinus

both in absolute (0.72 and 1.72 g) and in relative 

(10.9 and 21.9% body mass g–0.54) terms. Dry 

matter digestibility and metabolizable energy 

from seeds were similar between species on the ad 

libitum and 50% ad libitum water treatments and 

both species combined averaged 90.9% of dry 

matter and 88.8% of gross energy, respectively. 

These values were similar to those found for 

granivorous rodents in general. 

Downs, C. T. and M. R. Perrin. 1990. The effect of diet 

on water and energy turnover rates of four Gerbillurus 

species in captivity. Journal of Zoology 222:215-233. 

The effects of diets differing in energy and water 

content on the energy turnover rates and water 

flux of four Gerbillurus species live-trapped 

during 1986 and 1987in South West 

Africa/Namibia and the Cape Province, South 

Africa were examined in the laboratory. 

Gerbillurus tytonis, a dune species, had higher 

than predicted daily energy expenditure (DEE) 

and high water turnover rates (WTR) for a small 

desert mammal. The large G. setzeri, which 

occurs on gravel plains, has slightly lower than 

predicted DEE and WTR than the other gerbil 

species studied. The Gerbillurus species examined 

have DEE and WTR that are affected by the 

protein content and potential water yield of food 

eaten. The importance of diet selection for water 

and energy budgets are discussed as adaptive 

strategies employed for survival and reproduction 

within the southern African arid zone. 

Duxbury, K. J. and M. R. Perrin. 1992. Thermal biology 

and water turnover rate in the Cape gerbil, Tatera afra

(Gerbillidae). Journal of Thermal Biology 17:199-208. 

Oxygen consumption (VO2), thermal conductance 

(Cd and Cmin), body temperature (Tb) and 

evaporative water loss (EWL) of the Cape gerbil 

(Tatera afra) were measured in the laboratory at 

in the laboratory at the University of Natal, South 

Africa, at ambient temperatures (Ta) between 5 

and 35° C. T. afra is not well adapted to high Ta. 

Above 30° C, hyperthermia occurs, despite 

elevated Cd, Cmin and EWL. Peripheral 

vasodilation, salivation and urination are shortterm responses that contribute to delaying the 

onset of hyperthermia. The water turnover rate 

(WTR) is higher (48%) in the field than in the 

laboratory owing to activity associated with 

foraging behavior, predator avoidance and 

socialization. The relatively mild and mesic 

environment permits a higher WTR than in arid 

zone gerbils. Basal metabolic rate (BMR) is 

higher (49%) than the average value for other 

cricetid rodents. It is hypothesized that this is 

associated with herbivory and a relatively low Ta. 

Farrell, B. C. and D. P. Christian. 1987. Energy and 

water requirements of lactation in the North American 

porcupine, Erethizon dorsatum. Comparative 

Biochemistry and Physiology 88A:695-700. 

Energy and water requirements of lactation in the 

North American porcupine (Erethizon dorsatum) 

were studied at the University of Minnesota, 

Duluth. Energy and water requirements of 

lactating porcupines were compared with results 

of previous studies on energetics of reproduction 

in small-bodied rodents. Mass-specific food and 

water intake of control and lactating porcupines 

was examined throughout the 68 - 78 days of 

lactation. Water intake of lactating females was 

16% higher than that of non-lactating animals. 

Digestive efficiency of porcupines fed 

commercial rabbit chow was 54 - 60%; there was 

no significant difference in efficiency between 
97 

lactating and non-lactating animals. Total mean 

energetic intake throughout lactation was only 

17% greater than that of non-lactating animals. 

Reproductive rate and costs of lactation in 

porcupines are considerably less than in other 

rodents and other comparably sized mammals, but 

the amount of energy allocated to each offspring 

is quite high. The reproductive pattern of 

porcupines is associated with low juvenile 

mortality and long adult lifespan (both of which 

reflect the porcupine's protective morphology), 

and may be related to the quality of winter diets. 

Gettinger, R. D. 1984. Energy and water metabolism of 

free-ranging pocket gophers, Thomomys bottae. 

Ecology 65:740-751. 

Seasonal influences on the patterns of energy and 

water metabolism by free-ranging pocket gophers, 

(Thomomys bottae), were investigated using 3

H2

18O procedures. Metabolic rates of adult, 

nonreproductive gophers did not differ 

significantly in summer, winter, or spring (CO2, 

2.34 ml g-1 hr-1; 1416 kJ kg-1 day-1). Efficiency of 

energy assimilation (54%) by gophers consuming 

natural diets in the laboratory did not differ 

between summer and winter, even though 

composition of the diet changes seasonally. 

Calculated feeding rates (dry food, 119 g kg-1 day1

), also did not differ with season. Harvesting rates 

were more than two times feeding rates. 

Construction of energy budgets revealed that if 

annual vegetation is abundant, precluding the 

necessity for gophers to burrow extensively for 

food, energy is not limited in any season. Gophers 

remained in water balance (influx = efflux) in all 

seasons. However, influx was significantly greater 

during spring (518 ml kg-1 day-1) than during 

summer or winter (256 ml kg-1 day-1). In freeranging gophers, water influx was three to six 

times the minimum water flux of gophers than 

were maintained on water-restricted diets in the 

laboratory. In spite of their existence in arid 

macroenvironments, gophers appear to be "waterdependent." Diet selection and occupation of 

humid burrow systems appear to be prerequisites 

for existence in such habitats. 

Grenot, C. J. 1989. Ecophysiological characteristics of 

small mammals in arid zones (North America, Australia, 

Namibia, Sahara). Mammalia 53:478. (Abstract). 

A variety of physiological and behavioral 

solutions are employed by small mammals to 

challenge the desert environment. A comparative 

study of the ecophysiological responses to water 

stress was carried out with species from different 

arid regions. Various rodents conserve water and 

energy effectively, obtain adequate water, and 

energy throughout the year without drinking, by 

varying their diet appropriately among seed, 

vegetation and arthropods. Despite their 

taxonomic differences, ecophysical similarities 

can occur in various small mammals form 

different intercontinental arid regions. A rich 

diversity of desert adaptations remains to be 

found. It seems that each species copes differently 

in response to the highly variable and 

unpredictable climatic conditions. The plasticity 

of mammal physiology and behavior has been 

underestimated and future studies have to be 

pursued for each species, with the same 

methodology and careful control. 

Hayes, J. P., C. A. Bible, and J. D. Boone. 1998. 

Repeatability of mammalian physiology: evaporative 

water loss and oxygen consumption of Dipodomys 

merriami. Journal of Mammalogy 79:475-485. 

Phenotypic measurements (e.g., body mass, 

metabolic rate) made at 1 point in time are often 

assumed to represent measurements made at other 

times. However, if traits are not repeatable over 

time, inferences about ecological, environmental, 

or other correlates of the trait could be misleading. 

We found that evaporative water loss, oxygen 

consumption, resting metabolic rate, and their 

residuals from body mass were significantly 

repeatable (intraclass correlations generally > 0.6) 

in Merriam’s kangaroo rats (Dipodomys 

merriami). Nevertheless, our data, plus a review 

of the scant data on repeatability of mammalian 

physiological traits, show that repeatability 

typically is less than perfect (i.e., <1). 

Consequently, investigators studying 

physiological performance of mammals should 

not assume that the traits they study are good 

indicators of performance at other points in time. 
98 

Hewitt, S., J. F. Wheldrake, and R. V. Baudinette. 1981. 

Water balance and renal function in the Australian 

desert rodent Notomys alexis: the effect of diet on water 

turnover rate, glomerular filtration rate, renal plasma 

flow and renal blood flow. Comparative Biochemistry 

and Physiology 68A:405-410. 

Water balance and renal function were studied in 

the Australian desert rodent (Notomys alexis) at 

Flinders University, Australia. Water turnover 

rate, glomerular filtration rate and renal plasma 

and blood flow rates have been measured in 

individuals of the Australian desert rodent under 

conditions of acute and chronic water deprivation 

and high nitrogen diet. When these parameters are 

compared with values predicted allometrically the 

extreme ability of the species to conserve water is 

apparent only in those groups subjected to water 

stress. While a reversible reduction in renal 

function is evident upon water deprivation, the 

major function in water conservation under these 

conditions is the renal reabsorption of water at a 

post-filtration stage. 

Holleman, D. F. and R. A. Dieterich. 1973. Body water 

content and turnover in several species of rodents as 

evaluated by the titrated water method. Journal of 

Mammalogy 54:456-465. 

Body water content and turnover were determined 

for deer mouse (Peromyscus maniculatus), 

meadow vole (Microtus pennsylvanicus), tundra 

vole (M. oeconomus), insular vole (M. 

abbreviatus), vesper mouse (Calomys ducilla), 

collared lemming (Dicrostonyx groenlandicus), 

Egyptian spiny mouse (Acomys cahirinus), gerbil 

(Meriones unguiculatus), Norway rat (Rattus 

norvegicus), chinchilla (Chinchilla laniger), 

Guinea pig (Cavia porcellus), and muskrat 

(Odonata zibithicus) using the titrated water 

method. All experimental rodents were 

maintained under similar laboratory conditions. 

Measurements of body water content indicated 

wide variability in the degree of body fatness. 

Mean values of body fat as a percentage of body 

mass ranged from 3.0 to 38.8% for the 12 species. 

The equation, WTR = n (LBM)b

, was used to 

relate water transfer rate (WTR) to lean body 

mass (LBM). The overall exponent (b) for the 12 

species of rodents equaled 0.78 ± 0.044 (SD) and 

represents the interspecies estimate. The exponent 

computed for three species of the genus Microtus

equaled 0.69 ± 0.093. Specific water transfer rates 

ranged from 0.34 to 1.76 ml g-0.69 day-1. In 

general, water transfer rates ere correlated with 

water availability in the natural habitat of each 

species. Species inhabiting moist areas had higher 

specific water transfer rates while species 

inhabiting arid regions had lower specific water 

transfer rates. 

Horowitz, M. and J. H. Adler. 1983. Plasma volume 

regulation during heat stress: albumin synthesis vs. 

capillary permeability. A comparison between desert 

and non-desert species. Comparative Biochemistry and 

Physiology 75A:105-110. 

Plasma albumin synthesis was measured in rats 

(Rattus norvegicus) and sand rats (Psammomys 

obesus) during heat acclimation (34 oC) and 

following thermal dehydration (37 oC) in a 

laboratory using 3

H l-leucine as a tracer. In rats, 

heat acclimation resulted in 48% reduction in 

albumin synthesis. In sand rats, synthesis 

increased by 160%. Both species achieved a new 

stabilization of the synthetic system on the fifth 

day of acclimation. Following thermal 

dehydration albumin synthesis increased in rats 

and decreased in sand rats. Acclimation did not 

alter this response. In our dehydrating system 

plasma volume was maintained via maintenance 

of adequate albumin mass. In rats, albumin 

synthesis apparently contributes to this process. In 

sand rats, vascular permeability rather than 

albumin synthesis plays this role. 

Kam, M. and A. A. Degen 1992. Effect of air 

temperature on energy and water balance of 

Psammomys obesus. Journal of Mammalogy 73:207-

214. 

Fat sand rats (Psammomys obesus) are diurnal, 

desert-dwelling gerbillid rodents that can survive 

while consuming solely the saltbush (Atriplex 

halimus), a chenopod high in electrolytes. To 

reduce electrolyte intake, fat sand rats scrape off 

the outer layers of leaves with their teeth before 

consuming them. We measured energy and water 

balances of fat sand rats offered A. halimus and 
99 

maintained at 15, 21, and 34 oC. They maintained 

body mass at 21 oC, gained body mass at 34 oC, 

but lost body mass at 15 oC. The dry matter intake 

was not significantly different among treatments, 

but dry matter digestibility and metabolizable 

energy of A. halimus was higher for fat sand rats 

at 34 oC than at 15 and 21 oC. Fat sand rats at 34 

oC produced the most concentrated urine and 

scraped off the most leaf material. As a result 

these fat sand rats secreted the lowest volume of 

urine, thus providing them with water required for 

evaporative cooling. 

Kitahara, E. 1993. Relationships between habitat and 

renal function in water conservation in the Anderson's 

red-backed vole, Eothenomys andersoni on the Kii 

Peninsula, Japan. Japan. Forestry and Forest Products 

Research Institute Bulletin No 364:115-124. 

The present study on the distribution and renal 

structure of E. andersoni on the Kii Peninsula 

revealed the following: 1) the distribution of E. 

andersoni was vertically broad and horizontally 

limited to a certain range in a part of Nara, Mie 

and Wakayama Prefectures; 2) the distribution 

was strongly influenced by the amount of annual 

rainfall in the areas of Kii Peninsula, Japan, from 

1985 - 1990. E. andersoni alone occurred in areas 

whose annual rainfall exceeded 3,000 mm and 

coexisted with E. smithii in areas of about of 

about 2,500 to 3,000 mm, while only E. smithii

was caught in areas with a rainfall of less than 

2,000mm; and 3) there were significant 

differences (P<0.05) in the thickness (PMT) and 

area of the renal medulla measured at the 

midsagittal section between E. andersoni (PMT 

73.1 ± 2.3, PMA 41.3 ± 3.6, n = 6) and E. smithii

(PMT 77.7 ± 4.6, PMA 48.4 ± 4.9, n = 9); 

consequently E. andersoni had the weaker kidney 

against water shortage stress in comparison with 

E. smithii. 

Korine, C. and Z. Arad. 1993. Effect of water restriction 

on temperature regulation of the fruit-bat Rousettus 

aegyptiacus. Journal of Thermal Biology 18:61-69. 

The thermoregulatory responses of the fruit-bat 

(Rousettus aegyptiacus) were studied over a wide 

range of ambient temperature during normal 

hydration and during water restriction in Hiafa, 

Israel. The thermoneutral zone of the normally 

hydrated fruit-bat ranged between 31 - 36 oC. 

Oxygen consumption in this range averaged 0.95 

± 0.15 ml g-1 hr-1. Evaporative water loss and 

respiration frequency during normal hydration 

increased as power functions of ambient 

temperature and were significantly correlated (P < 

0.02). The normally-hydrated, heat exposed fruitbat effectively regulated its body temperature and 

dissipated the total metabolic heat production by 

evaporative cooling. In bats fed on oven-dried 

apples (water restriction), body mass decreased by 

20.72 ± 2.78%. Oxygen consumption between 32 

- 36 oC increased significantly and body 

temperature was relatively high. Evaporative 

water loss decreased significantly, except at 36 oC 

where evaporative water loss was not significantly 

different from that during normal hydration, 

suggesting the preference for body temperature 

regulation at the cost of increased water loss. At 

this ambient temperature, dry thermal 

conductance increased significantly compared to 

normal hydration, facilitating non-evaporative 

heat loss. We conclude that the Israeli population 

of Rousettus aegyptiacus is adapted to the 

relatively warm climate and can cope with 

decreased water content in its exclusive fruit diet 

and effectively regulate its body temperature and 

metabolic rate. 

Lindstedt, S. L. 1980. Energetics and water economy of 

the smallest desert mammal. Physiological Zoology 

53:82-97. 

The physiological and ecological coupling of the 

desert shrew (Notiosorex crawford) to its 

environment has been examined in wild captured 

shrews from Cochise and Pima counties, Arizona. 

Mean standard metabolism between 32 and 36 oC 

equaled 17.12 W/kg. Below 32 oC metabolic rate 

increased linearly to a high of 79 W/kg at 10 C. 

The heat transfer coefficient was 3.05 W kg-1 oC-1

below 32 oC. At 37 oC air temperature, heat lost 

by the evaporation of water equaled one-half of 

the total metabolic heat production. The kidney 

medullary thickness of the desert shrew is high, 

suggesting a considerable urine concentrating 

ability and only scant urinary water losses. By 

thus minimizing urinary and respiratory water 
100 

losses, the desert shrew can maintain water 

balance without drinking even when some water 

is required for thermoregulation. The climate 

space of the desert shrew was determined and 

found to differ from that of the masked shrew. 

The desert shrew can tolerate higher temperatures 

than can the masked shrew in full sunlight (23 vs. 

6 oC) in its nest (38 vs. 24 oC) and under the night 

sky (42 vs. 35 oC). Energy metabolism, water loss, 

and daytime activity are all lower in the desert 

shrew than in other shrew species. 

MacMillen, R. E. 1983. Water regulation in 

Peromyscus. Journal of Mammalogy 64:38-47. 

New-World mice of the genus Peromyscus are 

nearly ubiquitous, and their omnivorous diets are 

accompanied by intermediate efficiency in water 

regulation when compared to dry-food or moistfood specialists among rodents. In virtually all 

aspects of water economy thus far studied (mass 

and urinary responses to water deprivation and 

saline drinking solutions, rates of evaporative 

water loss), the performances of Peromyscus are 

modest, with the single exception of P. crinitus; 

this is a small desert rodent species that is nearly 

independent of dietary preformed water. Among 

Peromyscus there is considerable interspecific 

variability in efficiency of water regulation, and 

nearly as great intraspecific variability within west 

coast races of P. maniculatus. This variability 

appears to be related to food habits and/or habitat 

climate, but the specific roles of these factors have 

yet to be elucidated. The most striking adaptation 

to drought among Peromyscus is the use of torpor 

and summer dormancy by P. eremicus, enabling 

prolonged escape from demanding surface 

conditions of water stress. These thermoregulatory 

adjustments may be common among aridinhabiting Peromyscus and contribute 

substantially to their powers of water regulation. 

Mangione, A. M., D. Dearing, and W. Karasov. 1998. A 

plant secondary metabolite increases minimum water 

requirements of desert woodrats. American Zoologist 

38:114A. Final Program and Abstracts of the Annual 

Meeting of the Society for Integrative and Comparative 

Biology, Denver, Colorado, January 6-10, 1999 

(Abstract) 

The effects of plant secondary metabolites on 

water balance has received little attention. Desert 

woodrats (Neotoma lepida) fed a diet with 

phenolic resin extracted from creosote bush 

(Larrea tridentata) increased their ad libitum 

water intake (3 – 12 ml day-1) depending on diet 

resin concentration. This increase, if obligatory, 

would reflect at least a doubling of the minimum 

preformed water requirement of desert woodrats. 

The hypothesis that creosote bush phenolic resin 

would increase the minimum water requirements 

of woodrats was tested. In two experiments the 

minimum water requirement of woodrats fed dry 

diet (alfalfa pellets) with and without resin added 

was examined. Drinking water was offered in 

decreasing amounts until woodrats could just 

maintain constant body mass. In both experiments 

the minimum drinking water of woodrats fed resin 

was significantly higher than controls by about 

15% (ca. 1 ml day-1). Several potential causes of 

increased water loss associated with the increase 

in preformed water requirements were tested. 

Fecal water loss rate was significantly higher in 

woodrats eating resin. Neither water content of the 

urine, urine water loss rate, nor evaporative water 

loss rate was significantly affected by resin. 

McManus, J. J. 1974. Bioenergetics and water 

requirements of the redback vole, Clethrionomys 

gapperi. Journal of Mammalogy 55:30-44. 

The effects of temperature on food consumption, 

assimilation efficiency, oxygen uptake, and water 

requirements of the redback vole (Clethrionomys 

gapperi) were studied in a laboratory at Cornell 

University, Ithaca, New York. Gross and net 

caloric intakes varied inversely with temperature 

and the relationships were geometric rather than 

linear. Assimilation efficiency was maximal at 25 

oC (78.9%) and lowest at 10 oC (72.2%). 

Manometric measurements of oxygen 

consumption indicated a resting metabolic rate of 

31.4 ml O2 g-1 hr-1, a thermoneutral zone from 25 

to 28 oC, and a thermal conductance of 0.255 ml 

O2 g-1 hr-1 oC-1. Water consumption increased with 

temperatures above and below 15 oC. Minimum 

water requirements, including free water, food 

moisture, and metabolic water, were 0.64 g water 

g-1 day-1 at 15 oC. These date are compared to 

those of other small mammals. 
101 

Muller, E. F. 1979. Energy metabolism, 

thermoregulation and water budget in the slow loris 

(Nycticebus coucang, Boddaert 1785). Comparative 

Biochemistry and Physiology 64A:109-119. 

Energy metabolism, thermoregulation and water 

budget was studied in captive slow loris 

(Nycticebus coucang) in a laboratory setting. At 

ambient temperatures from 5 - 37 oC the mean 

rectal temperature varied from 32.2 - 38.5 oC. The 

thermoneutral zone extended from 25 - 33 oC, the 

basal metabolic rate (0.229 - 0.244 ml O2 g-1 hr-1) 

being only 40% of the mammalian standard. An 

excellent thermal insulation provided by the thick 

fur and a counter current heat-exchange in the 

limbs could be demonstrated. Thermoregulatory 

responses at ambient temperatures above 35 oC 

were insufficient, mainly due to restricted 

capacities for evaporative cooling. The daily fresh 

water consumption was very low (9 ml water day1

). The slow loris kidney is able to produce a 

rather highly concentrated urine (3,000 mOsm kg1

 water). The results were used to establish a daily 

energy budget under thermoneutral conditions. 

Mutze, G. J., B. Green and K. Newgrain. 1991. Water 

flux and energy use in wild house mice (Mus 

domesticus) and the impact of seasonal aridity on 

breeding and population levels. Oecologia 88:529-538. 

Water turnover rate (WTR), urine concentration 

and field metabolic rate (FMR) were examined in 

house mice, Mus domesticus, permanently 

inhabiting roadside verge areas and seasonally 

invading crops in semi-arid wheatlands in South 

Australia. FMR was approximately proportional 

to body mass 0.5 and mean values varied from 4.8 

ml CO2 g-1 hr-1 (2.9 kJ g-1 day-1) in autumn and 

winter, to 7.0 ml CO2 g-1 hr-1 (4.2 kJ g-1 day-1) in 

maturing crops during spring. WTR was 

independent of body mass, indicating that larger 

mice were selecting a diet containing moister 

foods. WTR was low in summer and high in 

winter, and in mice from crops varied from 165 

ml L-1 body water day-1 (122 ml kg-1 day-1) to 

1,000 ml L-1 day-1 (725 ml kg-1 day-1). Seasonal 

changes in WTR were less extreme on the 

roadside, where a greater diversity of food was 

available. In the crops, breeding occurred 

throughout the summer during two of three years, 

but the population increased only in the one 

summer when mice had marginally higher WTR. 

On the roadside, breeding and population growth 

were continuous during summer, except in a 

drought year. Average urine concentration was 

inversely related to WTR, and varied form 2.0 to 

4.8 osm L-1. The data indicate that the water 

conserving abilities of mice equal those of many 

desert rodents. The water conserving abilities of 

mice living in crops during summer were fully 

extended, and in some year aridity limited 

breeding success and population levels. The 

degree of moisture stress to which mice are 

exposed during summer appears to depend not 

only on rainfall but also on other factors such as 

availability of food and shelter, and the level of 

weed infestation in crops. 

Nagy, K. A. 1994. Seasonal water, energy and food use 

by free-living, arid-habitat mammals. Australian Journal 

of Zoology 42: 55-63. 

In arid ecosystems, the dry season is probably an 

especially challenging time for animals to find 

adequate food and water resources. Both stressful 

and benevolent times of the year can be identified 

by measuring rates of water and energy use (with 

doubly labeled water), diet and behavior 

throughout a year in free-ranging animals. 

Seasonal water, energy and food use were studied 

in free-living jackrabbits (Lepus californicus), 

Merriam’s kangaroo rats (Dipodomys merriami), 

and antelope ground squirrels 

(Ammospermophilus leucurus) in the Mojave 

Desert, California, and springbok, antelope 

(Antidorcas marsupialis) in the Kalahari 

Gemsbok National Park in Southern Africa. 

Jackrabbits are strict herbivores, and most Mojave 

Desert individuals have no access to drinking 

water, and depend on their food for their water. 

When vegetation dries up during the summer 

drought, most jackrabbits apparently die of 

dehydration and malnutrition, but populations are 

replenished by bountiful reproduction after winter 

rains. However, springbok antelope, also strict 

herbivores, can maintain water and energy 

balance throughout the year in the Kalahari in 

southern Africa by drinking water is available, 

but, if not, they obtain enough water from dietary 

plants, probably by feeding before dawn, when 
102 

food items have taken up water from the humid 

air. Antelope ground squirrels are omnivorous in 

the Mojave Desert, and are active diurnally. They 

have lower water and energy requirements than 

non-desert mammals of the same body mass, like 

many desert mammals, but their ability to find 

succulent plant or animal foods in all seasons 

appears to be their primary survival tool. On the 

other hand, Merriam's kangaroo rats are 

essentially nocturnal, and were thought to be strict 

granivores that never drank. A recent study, done 

throughout a year in the Mojave Desert, confirms 

their lack of drinking, but revelas that they eat 

much green vegetation in late winter and spring, 

probably in connection with reproduction. They 

obtain additional water throughout the year by 

caching dry seeds in humid burrows, where seeds 

take up water hydroscopically before being eaten. 

Although springbok, antelope ground squirrels 

and Merriam's kangaroo rats were in negative 

energy and water balance at times during the year, 

only jackrabbits were severely stressed by the dry 

season. Each species has a unique suite of desert 

survival mechanisms. Future research should 

include carnivores as well as arid-habitat 

marsupials. 

Nagy, K. A. and M. J. Gruchacz. 1994. Seasonal water 

and energy metabolism of the desert-dwelling kangaroo 

rat (Dipodomys merriami). Physiological Zoology 

67:1461-1478. 

Free-living Merriam’s kangaroo rats (Dipodomys 

merriami) were studied in the Mojave Desert, 

California in 1988 – 1989; kangaroo rats did not 

drink, even when abundant rainwater was 

available for short periods in winter and summer, 

but they still obtained much more water than 

expected from a diet of dry seeds alone. Yearround measurements of water influx rates and 

field metabolic rates (via doubly labeled water), 

diet composition (stomach content analysis), and 

body mass changes were used to evaluate water 

and energy balance during each month of the year. 

From late spring (May) through midwinter 

(December), kangaroo rats ate primarily the seeds 

of creosote bush (Larrea tridentata) and were able 

to maintain water and energy balance on this diet 

even during summer drought. Dry seeds collected 

at the surface apparently were cached in burrows 

where hydroscopic uptake of water from humid 

air increased the succulence of seeds before 

ingestion. In late winter and early spring, 

kangaroo rats obtained abundant water and energy 

from their diet of green vegetation (90% dry 

mass) and arthropods (10%). Only in late April 

and early May did these animals lose body mass, 

but that was primarily due to reproductive effort 

(lactation) by females. Thus, at no time of year 

were kangaroo rats distressed by their 

comparatively dry, hot, and barren desert habitat. 

Field metabolic rates were highest in winter, 

which suggests that these animals did not use 

torpor or hibernation. On an annual basis, an 

individual free-living kangaroo rat (mean body 

mass 33.9 g) consumed nearly 1 kg (dry matter) of 

food, and population (density, 17.5 animals ha-1) 

consumed over 17 kg ha-1. This is a small fraction 

of net primary productivity but can be a large 

proportion of seed production. 

Nagy, K. A., V. H. Shoemaker, and W. R. Costa. 1976. 

Water, electrolyte, and nitrogen budgets of jackrabbits 

(Lepus californicus) in the Mojave Desert. Physiological 

Zoology 49:351-363. 

Seasonal changes in water flux rates and diet 

(stomach content analysis) were determined in 

jackrabbits (Lepus californicus) kept in 0.4 ha 

field enclosures that contained natural Mojave 

Desert vegetation in San Bernardino County, 

California. The water, electrolyte, and nitrogen 

contents of food plants were measured at different 

seasons. Itemized water, electrolyte, and nitrogen 

budgets in jackrabbits were obtained by 

measuring food utilization in caged animals fed 

natural diets. Field jackrabbits maintained body 

mass and obtained excess water while eating 

succulent annual plants in spring, but in summer 

and winter animals could not maintain mass or 

water balance while eating the drier vegetation 

present during those seasons. Diet utilization 

studies indicated that (1) jackrabbits could not 

maintain nitrogen balance on the winter diet, (2) 

ion regulation was no problem in spring or 

summer, and (3) jackrabbits can produce fairly 

concentrated urine (2.5 - 3.6 osm), very dry feces 

(38% water), and can reduce evaporative water 

loss about 70% when water is restricted. Despite 

these mechanisms for conserving water, 
103 

jackrabbits in the field have relatively high water 

requirements. We estimate that in summer a 

jackrabbit would require about 120 ml water kg-1 

day-1 to maintain water balance, and that its diet 

must contain no less than 68% water in order to 

meet this requirement. As long as food plants 

contain sufficient water, their digestibility, 

nitrogen, and electrolyte content will probably 

also be suitable. 

Reese, J. B. and H. Hines. 1978. Effects of dehydration 

on metabolic rate and fluid distribution in the jackrabbit, 

(Lepus californicus). Physiological Zoology 51:155-165. 

Jackrabbits (Lepus californicus) captured in 

Oklahoma and New Mexico were used to study 

the effects of dehydration on metabolic rate and 

fluid distribution in a laboratory setting at the 

University of Oklahoma. Chronic water restriction 

resulted in a 30% decrease in metabolic rate and 

an over 50% decrease in evaporative loss in 

jackrabbits with no change in body temperature. 

Thus, evaporative cooling as a means of 

maintaining body temperature was minimized. 

Accommodation to measuring technique may 

account for part of the decrease in O2

consumption. Fractional water content increased, 

and solids decreased associated with a 10.6% 

weight loss due to a chronic restriction, whereas 

plasma and extracellular volume decreased in 

proportion to weight loss. The biological half-life 

of water was increased from 5.8 to 11.6 days 

while water exchange decreased from 13.0% to 

5.9% of the body water per day. In acutely 

dehydrated jackrabbits (3 - 5 days without water 

at 25 oC), all body fluid compartments lost equal 

proportions (10.7%) with no change in metabolic 

rate. Similarly, oxygen consumption was 

unaffected, and plasma volume decreased in 

proportion to weight loss (5.5%) in jackrabbits 

acutely dehydrated in hyperthermic conditions (12 

- 14 hr at 35 - 40 oC). The jackrabbit is similar to 

several other desert species in that it minimizes 

the loss of plasma volume when exposed to 

several other desert species in that it minimizes 

the loss of plasma volume when exposed to 

dehydration. Evan’s Blue space of 8.6% of body 

mass was shown to be a 36% overestimation of 

plasma volume as measured with iodinated (125I) 

albumin (6.3% of body mass). 

Reid, E. D. and R. J. Brooks. 1994. Effect of water on 

retention time and food consumption in deer mice. 

Canadian Journal of Zoology 72:1711-1714. 

Experiments were conducted to assess the effect 

of water on food consumption and retention time 

in deer mice (Peromyscus maniculatus). We 

tested whether increased intake of water, 

preformed in food or free drinking water, affects 

mean retention time and consumption of food. 

Mean retention times for diets of sunflower seeds 

(Helianthus annuus), commercial rat chow, and 

insect-seed mixtures were estimated by using 2-

mm red thread markers. For all diets, mean 

retention times decreased more rapidly with 

increased water content for sunflower seeds than 

for rat chow, suggesting that food type also may 

be important. Granivorous rodents may consume 

wet food items during periods of low water 

availability to increase energy intake rather than 

to satisfy water requirements. 

Rhodes, D. H. and M. Richmond. 1987. Water 

metabolism in free-ranging pine voles (Microtus 

pinetorum). Comparative Biochemistry and Physiology 

86A:213-215. 

Water metabolism in free-ranging pine voles 

(Microtus pinetorum) was studied in 1981-1982 in 

New Paltz, New York. Rates of body water 

turnover in free-ranging pine voles exceeded those 

reported for a large number of similarly sized 

mammals. Concentration of urine obtained from 

free-ranging pine voles were significantly lower 

than values published for other free-ranging 

mammals and also for laboratory-maintained 

members of this species. Rates of body water 

turnover in this species were not correlated with 

seasonal changes in soil temperatures. 

Richards, G. C. 1979. Variation in water turnover by 

wild rabbits, Oryctolagus cuniculus, in an arid 

environment, due to season, age group and 

reproductive condition. Australian Wildlife Research 

6:289-296. 

Rates of water turnover were measured in freeliving rabbits (Oryctolagus cuniculus) during a 

period of wide variation of climate and water 
104 

availability in New South Wales, Australia. Mean 

rate of water turnover was positively correlated 

with the hydration of the pasture (r = 0.987). 

Mean turnover rates per day ranged from 214.3 ml 

kg-1 in cool, wet conditions to 55.4 ml kg-1 in a 

moderate summer drought. The lowest individual 

rate was 46.1 ml kg-1 day-1. The rate of water 

turnover in young rabbits (1-2 months old) was 

significantly higher than that of adults measured 

at the same time; this may contribute to the low 

survival of young rabbits in dry seasons. A 

comparison of the rates of water turnover from 

lactating rabbits in wet and dry season shows that 

the estimated milk production under dry pasture 

conditions is below that required to maintain a 

litter of young. 

Sasidharan, T. O., S. P. Goyal, P. Chand, and P. K. 

Ghosh. 1990. The effects of water deprivation and salt 

load on water conservation efficiency in two Indian 

desert gerbils. Journal of Comparative Physiology 

160B:413-422. 

The effects of water deprivation and 

intraperitoneal salt loading on urine volume and 

on various urinary constituents have been 

examined in 2 gerbil species of the Rajasthan 

Desert, the Indian desert gerbil (Meriones 

hurrianae) and the Indian gerbil (Tatera indica 

indica Hardwicke). During summer, hydrated T. 

indica excreted 0.782 ml urine 100g-1 day-1, which 

was about 60.5% higher than the volume of urine 

excreted by hydrated M. hurrianae (0.487 ml 

100g-1 day-1). During winter, both species excreted 

around 1.5 ml urine 100g-1 day-1. The 

experimental treatments caused reductions in 

urine volume in M. hurrianae from 40 to 76% 

during summer and from 35 to 71% in winter. 

Similar treatments in T. indica caused reductions 

in urine volume of 50 - 82% in summer and 5-

60% in winter. The mean increase in urine 

osmolarity following various salt loading 

treatments in T. indica ranged form 3,800 to 5,761 

mOsm and from 4,034 to 6,255 mOsm during 

summer and winter, respectively. The mean 

values of urine osmolarity for hydrated T. indica

were 2,831 and 3,189 mOsm during summer and 

winter, respectively. In M. hurrianae salt loading 

treatments caused increases of urine osmolarity 

between 3,381 and 5,646 mOsm and between 

4,032 and 5,434 mOsm during summer and 

winter, respectively, over the values recorded for 

hydrated animals (summer = 3,292; winter = 

3,294 mOsm). A maximum urine osmolarity of 

around 7,000 mOsm was found in both species 

when subjected to 2% salt loading treatment. The 

treatments used in this study increased urinary 

urea level in both T. indica (3,039 – 4,056 mM) 

and in M. hurrianae (1,900 - 2,180 mM) 

compared to the level in their respective hydrated 

controls (T. indica = 1,628 mM; M. hurrianae = 

1,372 mM). The results indicate that T. indica

may be better adapted to produce more 

concentrated urine than M. hurrianae. 

Seymour, R. S., P. C. Withers, and W. W. Weathers. 

1998. Energetics of burrowing, running, and free-living 

in the Namib Desert golden mole (Eremitalpa 

namibensis). Journal of Zoology, 244:107-117. 

The Namib Desert garden mole (Eremitalpa 

granti namibensis) is a small (ca. 20g), blind, 

sand-swimming, chrysochlorid insectivore that 

inhabits the sand dunes of one of the driest and 

least productive areas of the world. Its food, 

largely termites, is sparse and occurs in widely 

distributed patches, and free water is unavailable. 

The moles forage by running on the surface and 

burrowing below the sand. Moles were livecaptured at the Kuiseb River, Namibia in 1996. 

We estimated their daily energy expenditure in the 

field to be 11.8 kJ day-1 by constructing a 

"distance-energy budget" based on measurements 

of tracks in the sand and the energy cost of 

running (4.2 kJ day-1), burrowing (3.2 kJ day-1), 

and resting (4.4 kJ day-1). We also measured field 

metabolic rate (12.5 kJ day-1) and water turnover 

(2.3 ml day-1) independently with doubly-labeled 

water. The resting metabolic rate (0.5 ml O2 g hr-1

at 35 oC) is about a fifth of that predicted for a 

normal insectivorous mammal, and the daily field 

energy expenditure and water turnover are about a 

half. The low daily energy expenditure stems 

mainly from the low resting metabolic rate, which 

is associated with low body temperatures and 

metabolic depression. Moles save more energy 

during foraging by running on the surface of the 

sand, rather than burrowing under it. The gross 

energy cost of sand-swimming (80 J m-1) is 26 

times more expensive than running on the surface 
105 

(3.0 J m-1), but is less than a tenth of the energy 

required by mammals that tunnel through compact 

soil. Nevertheless, it would be energetically 

impossible for the moles to obtain enough food by 

foraging only underground at our study site. The 

mean track length was 1.4 km, but only 16 m of it 

was below the surface. There is evidence that the 

track length and fraction underground depend on 

food abundance, which is influenced by rainfall. 

Schmidt-Nielsen, B. and K. Schmidt-Nielsen. 1950. 

Pulmonary water loss in desert rodents. American 

Journal of Physiology 162:31-36. 

Water evaporation was measured in Merriam 

kangaroo rat (Dipodomys merriami), banner-tailed 

kangaroo rat (D. spectabilis), pocket mouse

(Perognathus sp.), Norway rat (Rattus 

norvegicus), Syrian golden hamster (Cricetus 

aureus), canyon mouse (Peromyscuc crinitus),

and house mouse (Mus musculus). Evaporation 

from the lungs was 0.54, 0.57, 0.50, 0.94, 0.85, 

0.59, and 0.54 mg water ml-1 O2 in Merriam 

kangaroo rat, Banner-tailed kangaroo rat, pocket 

mouse, Norway rat, house mouse, Syrian golden 

hamster, and canyon mouse, respectively. In 

desert rodents, hamsters, and wild mice 

pulmonary evaporation was considerable less than 

in Norway rats and house mice and is likely an 

adaptation to maintaining water balance. 

Schmidt-Nielsen, B. and K. Schmidt-Nielsen. 1957. A 

complete account of the water metabolism in kangaroo 

rates and experimental verification. Journal of Cellular 

and Comparative Physiology 38:165-181. 

A complete account of the water intake and water 

output of Merriam’s kangaroo rats (Dipodoyms 

merriami) maintained on a dry grain diet is 

presented. Calculations are based on data of 

evaporative water loss and urine concentration 

presented in previous publications and on 

additional data on water loss through and moisture 

determinations in pearled barley fed to the 

animals. Kangaroo rats are in positive water 

balance when fed a diet of dry pearled barley 

without drinking water at all atmospheric 

humidities above 2.2 mg water L-1 air (10% 

relative humidity at 25 oC). Kangaroo rats could 

not maintain body mass below atmospheric 

humidities of 2.5 mg water L-1 air. White rats 

(Rattus norvegicus) fed the same diet were in 

negative water balance and were unable to 

maintain body mass at all atmospheric humidities 

below 21 mg water L-1 air. 

Stalling, D. T. and H. Haines. 1982. Effect of 

dehydration on water-turnover rates and hematocrits in 

the rice rat, Oryzomys palustris. Comparative 

Biochemistry and Physiology 72A:301-306. 

Effect of dehydration on water-turnover rates and 

hematocrits was studied in the rice rat (Oryzomys 

palustris). Water turnover rate (WTR) was 

determined in rice rats, using titrated water, under 

conditions of ad libitum water (hydrated), water 

restriction (dehydrated), and restoration of ad 

libitum water (rehydrated). Hydrated WTR's were 

similar to other mesic rodents, but water 

restriction revealed this species inability to 

conserve water. WTR's of hydrated, dehydrated, 

and rehydrated animals in ml kg-0.82 day-1 was 

140.3, 94.9 and 158.1 respectively. Hematocrit 

decreased during dehydration, possibly due to red 

cell loss. Hematocrit in rice rats was high as 

compared to cricetid rodents (50 vs. 44% in 

similarly sized cricetids) and this was evaluated as 

an adaptive feature. 

Stallone, J. N. 1979. Seasonal changes in the water 

metabolism of woodrats. Oecologia 38:203-216. 

Seasonal changes in the water metabolism of 

dusky-footed (Neotoma fuscipes) and desert 

woodrats (N. lepida) was studied in San Diego 

County, California in 1972 - 1973. The effects of 

seasonal aridity upon the water conserving 

abilities of these species were assessed through 

measurements of water conserving abilities and 

kidney structure of animals captured in summer 

and winter, and through measurements of animals' 

abilities to acclimate to differing water 

availabilities in the laboratory. Urine 

concentrating ability was the water conserving 

mechanism most responsive to changes in the 

availability of water. Summer and summeracclimated N. fuscipes (431.7 and 459.4 meq Cl L1

) demonstrated urine Cl concentrating abilities 
106 

substantially greater than those of winter and 

winter-acclimated N. fuscipes (245.7 and 337.4 

meq Cl L-1). Summer, winter-acclimated, and 

winter N. lepida exhibited urine Cl concentrations 

equivalent to those of winter N. fuscipes; summeracclimated N. lepida exhibited markedly greater 

values (466.7 meq Cl L-1) equivalent to those of 

summer and summer-acclimated N. fuscipes. 

Measurement of relative thickness of renal cortex 

and medulla yielded no significant differences 

among the experimental groups of N. fuscipes and 

N. lepida, thus suggesting that both species 

possess equal abilities to concentrate urine. These 

data are confirmed by urine concentrations of 

summer-acclimated animals of both species. 

Water conserving abilities of both species 

correlate well with climatic and dietary plant 

water content data. Thus, during the dry, warm 

summer months (when plant moisture is reduced) 

N. fuscipes conserves water mainly through 

increased urine concentration. The laboratory 

acclimation data and differences between summer 

and winter animals strongly suggest that N. 

fuscipes undergoes an acclimatization to the 

seasonal aridity which increases gradually during 

summer and peaks in late summer, thus enabling 

this water-dependent species to exist on reduced 

water requirements. The uniformly low water 

conserving abilities of winter-acclimated, winter, 

and summer N. lepida physiologically verify the 

previous reports that this species satisfies its water 

requirements through utilization of succulent 

cactus, thereby avoiding the stress of summer 

aridity in its habitat. The fact that both species 

exhibit equal capacities to conserve water 

indicates that the much greater geographic 

distribution of N. lepida is not the result of 

differences in physiological water conserving 

abilities, but instead may be the result of specific 

physiological adaptation by N. lepida to 

utilization of cactus and other plants containing 

noxious or toxic compounds. 

Tracy, R. L. and G. E. Walsberg. 2000. Unappreciated 

tolerance to high ambient temperatures in a widely 

distributed desert rodent, Dipodomys merriami. 

Physiological and Biochemical Zoology 73:809-818. 

A long-held assertion has been that nocturnality is 

an escape mechanism for many nocturnal desert 

rodents because of limited tolerances to heat. To 

test this claim, we used a treadmill to examine the 

tolerances to high ambient temperatures (Tas) of 1 

subspecies of desert rodent, Merriam's kangaroo 

rat, (Dipodomys merriami merriami) from 

contrasting environments in Yuma and Gila 

counties, Arizona, and in the laboratory at 

Arizona State University, Tempe, Arizona. We 

simultaneously measured body temperature (Tb), 

evaporative water loss, and metabolic rates at an 

ecologically relevant speed (0.6 km hr-1) at 

different ambient temperatures (Ta = 25 - 42.5 oC). 

We hypothesized that kangaroo rats from a more 

xeric site would have greater abilities to remain 

active and maintain stable Tb than those from a 

more mesic site, but mesic and xeric-site animals 

had comparable tolerances and were active until 

Tb = 42 oC. At Ta = 42.5 oC, however, Tb of mesicsite animals increased more quickly than in xericsite animals. Although most animals could not run 

more than 18 min at Ta = 42.5 oC, most could run 

at Ta = 40 oC for at least 30 min. Benefits of 

nocturnality for this species may reside more in 

purposes of water conservation and avoidance of 

predation and less on the direct regulation of Tb as 

Tb is more labile than commonly thought. 

Turlejska, E. and J. Lyszczarz. 1986. Dehydration does 

not influence the summer versus winter thermal 

adaptation changes in rabbits (Oryctolagus cuniculus) 

living in natural photoperiod. Journal of Thermal Biology 

11:41-45. 

Resting metabolic rate of laboratory rabbits kept 

indoors is susceptible to seasonal fluctuations and 

is higher than in summer. Thermoneutral zone of 

rabbits under these conditions may shift 

downwards in winter and upwards in summer. 

Both of these adjustments in thermoregulation 

seem to be related to the seasonally changing 

photoperiod. Dehydration did not influence these 

thermoregulatory adaptive changes. 

Vorhies, C. T. 1945. Water requirements of desert 

animals in the southwest. Technical Bulletin 107. 

University of Arizona, Agricultural Experiment Station, 

Tucson, Arizona, USA. 
107 

Abiotic characteristics (e.g. temperature, relative 

humidity) of microclimates used by and food 

habits of banner-tailed kangaroo rat (Dipodomys 

spectabilis), wood rat (Neotoma albigula), roundtailed ground squirrel (Citellus tereticaudus), and 

jackrabbits (Lepus spp.) were studied on the Santa 

Rita Experimental Range, Arizona in relation to 

water conservation and heat balance. Comparisons 

are also made between the microclimate 

conditions of mesquite (Prosopis velutina) and the 

surrounding desert. 

Willems, N. J. and K. B. Armitage. 1975. 

Thermoregulation and water requirements of semiarid 

and montane populations of the least chipmunk, 

(Eutamias minimus)--ii. Water balance. Comparative 

biochemistry and physiology 52A:109-120. 

Acclimation of semiarid and montane populations 

of the least chipmunk (Eutamias minimus) at a 

high ambient temperature was studied. 

Acclimatization at 34 oC results in a reduction of 

metabolism, body temperature (Tb), and 

evaporative heat loss (EHL) and an increase in dry 

heat conductance as compared to values reported 

for chipmunks acclimatized at 22 oC. At high 

ambient temperatures, the semiarid population, as 

compared to the montane population, maintains a 

lower Tb under all conditions examined. The 

lower Tb occurs because of a higher EHL when 

water is available and because of reduced 

metabolism when dehydrated. Adaptation of E. 

minimus to the semiarid habitat has involved 

changes in response to acute and chronic heat and 

water stress, which increase the time the 

chipmunks, can survive exposures to high ambient 

temperature, regardless of water availability. 

Withers, P. C. 1963. Effect of diet and assimilation 

efficiency on water balance for two desert rodents. 

Journal of Arid Environments 5:375-384. 

Differences in preformed water content and 

digestive assimilation efficiency of three diets, 

millet seed, soy bean and bran had profound 

effects on energy balance and water balance in 

two species of North American desert rodents, 

Peromyscus maniculatus and Perognathus parvus

captured in central and eastern Oregon in 1980. 

Digestive assimilation efficiency was over 90% 

for millet, 85% for soybean and 65% for bran. 

The assimilation efficiency was correlated with 

the fiber content of the diet. The daily energy 

assimilated by animals with ad libitum water was 

similar for the three diets. Both species survived 

chronic water deprivation when consuming seed, 

but not when consuming soybean or bran. 

Tolerance to water deprivation was inversely 

related to assimilation efficiency. This is 

attributed to the high fecal water loss of mice 

consuming soybean or bran, since fecal water loss 

is inversely proportional to assimilation 

efficiency. A low digestive assimilation efficiency 

automatically precludes the concomitant 

maintenance of positive water and energy balance 

for animals without available drinking water. 

Yahav, S., S. Simson, and E. Nevo. 1989. Total body 

water and adaptive water turnover rate in four 

chromosomal species of subterranean mole rats of the 

Spalax ehrenbergi superspecies in Israel. Journal of 

Zoology 218:461-469. 

Total body water (TBW) and water turnover rate 

(WTR) were measured in 24 subterranean mole 

rats comprising 4 populations, each belonging to a 

different chromosomal species of the (Spalax 

ehrenbergi) superspecies in Israel. The 4 species 

range in different climates: humid-cool percentage 

of body mass, measured by titrated water (HTO), 

was 72.4% ± 4.7, significantly (P < 0.05) higher 

than the similar estimates of 61.7% ± 7.2, and 

59.4% ± 5.3, respectively. A comparison of HTO 

space, as a percentage of TBW, closely 

approximated TBW, ranging from 97% to 108%. 

WTR was high, 218.1 and 230.9 ml kg-0.75 day-1 in 

the mesic populations of. By contrast, WTR 

estimates were significantly lower, (P < 0.001), 

150.2 and 148.9 ml kg-0.75 day-1 in the xeric 

populations, respectively. The biological half-life 

time was similar and faster, 32.7 and 27.9 hours in 

the mesic populations, as compared with slower, 

47.9 and 40.8 hours in the xeric populations. 

Urine osmolality (737 ± 45 mmol kg-1) in the most 

xeric northern Negev steppe populations was 

significantly (P < 0.001) higher than in the other 

species. We conclude that adaptive radiation in 

the Spalax ehrenbergi superspecies involves 

speciation in semiarid and arid climates by the 
108 

physiological adaptations of kidney water 

conservation, along with multiple morphological, 

physiological and behavioral syndromes of 

climatic adaptations to increasing aridity. 

Yousef, M. K., H. D. Johnson, W. G. Bradley, and S. M. 

Seif. 1974. Titrated water-turnover rate in rodents: 

desert and mountain. Physiological Zoology 47:153-

162. 

Water-turnover rate in were studied in rodents 

desert and mountain environments suing titrated 

water. Eight species of rodents were studied; 

species arranged in increasing order of daily water 

turnover rates are: Dipodomys deserti, D. 

merriami, D. microps, Spermophilus tereticaudus, 

Ammospermophilus leucurus, Neotoma lepida, 

Spermophilus lateralis, and Eutamius palmeri, 

were studied. Influences of phylogeny, ecologic 

distribution, diet, behavior, and metabolic rate on 

water turnover rates are discussed. 

Zhi-long, L., L. Zhong-min, and S. Ru-yong. 1992. 

Seasonal water turnover rates of free-living Brandt’s 

voles Microtus brandti. Physiological Zoology 65:215-

225. 

Seasonal changes in water turnover rates were 

determined in free-living Brandt’s voles (Microtus 

brandti) of arid steppes of inner Mongolia using 

isotopically labeled water method. The water flux 

of laboratory-maintained Brandt’s voles was also 

measured. Voles remained in water balance in all 

seasons. Water influx of free-living voles was 

lowest in April (180 ml kg-1 day-1) and highest 

during June and August (270 ml kg-1 day-1 and 280 

ml kg-1 day-1, respectively). The pattern of 

seasonal changes of water turnover rates of freeliving Brandt’s voles was similar to that of other 

herbivores. Water influx during October (217 ml 

kg-1 day-1) was higher than that during April. 

Foraging and burrow digging activity are 

suggested as reasons for this increase. Also, the 

months of March and April may be the waterstressed period. 

Techniques and Methodology 

Holleman, D. F., R. G. White, and J. R. Luick. 1982. 

Application of the isotopic water method for measuring 

total body water, body composition, and body water 

turnover. Pages 9-32 in Use of titrated water in studies 

of production and adaptations in ruminants. 

International Atomic Energy Agency, Vienna, Austria. 

The theory and application of the isotopic water 

method in body water and body composition 

studies are discussed, including the underlying 

assumptions and the effects of inaccuracies and 

the problems of recycling. The application of the 

method for estimating intake of water and water 

additives is outlined. 

Knox, K. L., A. Chappell, J. A. Gibbs, D. N. Hyder, and 

R. E. Bement. 1970. Sampling methods for water 

kinetics. Journal of Dairy Science 53:1279-1282. 

In a Holstein steer, jugular blood, saliva, 24-hour 

urine collection, urine by palpation, and respiredwater were compared to determine their reliability 

and convenience for tritium assay in water kinetic 

studies. No significant differences in rate of 

tritium dilution occurred among the various 

procedures. However, the collection and assay of 

respired-water was the most convenient method. 

Further comparison of jugular blood and respiredwater collected from 12 lambs revealed no 

significant difference in tritium dilution. 

Lifson, N. and R. McClintock. 1966. Theory of use of 

the turnover rates of body water for measuring energy 

and material balance. Journal of Theoretical Biology 

12:46-74. 

The theory is developed for the use of the 

isotopically determined turnover rates of the 

hydrogen and oxygen of body water for 

measurement of total energy and material balance 

of an animal. After a consideration of several 

simplifying assumptions, a summary is given of 

tests of the extent to which theoretical 

expectations are realized. The results of these 

appear to be in general accord with theoretical 

expectations. 
109 

Nagy, K. A. 1975. Water and energy budgets of freeliving animals: Measurement using isotopically labeled 

water. Pages 227-245 in N. F. Hadley, editor, 

Environmental physiology of desert organisms. 

Dowden, Hutchinson, and Ross, Inc. Stroudsburg, 

Pennsylvania, USA. 

This book chapter reviews techniques used to 

measure water, energy, and material fluxes in 

free-living animals using isotopically labeled 

water. It briefly covers methodologies, water and 

energy budgets, water flux calculations, metabolic 

rate calculations, isotope assays, and potential 

sources of error. It also contains a discussion of 

results of labeled water studies with reference to a 

study conducted on chuckwalla (Sauromalus 

obesus). 

Nagy, K. A. 1980. CO2 production in animals: analysis 

of potential errors in the doubly labeled water method. 

American Journal of Physiology 238:R466-473. 

Laboratory validation studies indicate that doubly 

labeled water measurements of CO2 production 

are accurate to within ± 8% in 9 species of 

mammals and reptiles, a bird, and an insect. 

However, in field studies, errors can be much 

larger under certain circumstances. Isotopic 

fraction of labeled water can cause large errors in 

animals whose evaporative water loss comprises a 

major proportion of total water efflux. Input of 

CO2 across lungs and skin caused errors 

exceeding +80% in kangaroo rats exposed to air 

containing 3.4% unlabeled CO2. Analytical errors 

of ±1% in isotope concentration can cause 

calculated rates of CO2 production to contain 

errors exceeding ± 70% in some circumstances. 

These are 1) when little decline in isotope 

concentrations has occurred during the 

measurement period, 2) when final isotope 

concentrations closely approach background 

levels, and 3) when the rate of water flux in an 

animal is high relative to its rate of CO2

production. The following sources of error are 

probably negligible in most situations: 1) use of 

an equation that does not correspond to the 

patterns of change in total body water, 2) 

variations in rates of water or CO2 flux through 

time, 3) use of 2

H2

18O dilution space as a measure 

of body water volume, 4) exchange of 18O 

between water and organic compounds in animals 

(including excrement), 5) incomplete mixing of 

isotopes in the animal, and 6) input of unlabeled 

water via lungs and skin. Errors in field 

measurements of CO2 production can be related to 

acceptable levels (<10%) by appropriate selection 

of study subjects and recapture intervals. 

Nagy, K. A. and C. C. Peterson. 1988. Scaling of water 

flux rates in animals. University of California Press, 

Berkeley, California, USA. 172p. 

Studies of water flux rates measured using titrated 

or deuterated water in eutherian and marsupial 

mammals, birds, reptiles, fishes, arthropods, and 

mollusks were summarized and analyzed 

allometrically. Water flux is strongly correlated 

with body mass within taxa and scales differently 

in captive vs. free-living animal, among animals 

in different taxa, and among animals having 

different habitats and diets. This indicates that 

ecological conclusions based on laboratory studies 

of captive animals are suspect. Water fluxes are 

highest in water-breathing animals, intermediate 

in air-breathing endotherms, and lowest in airbreathing ectotherms. Analyses of the water 

economy index (amount of water used per unit 

energy metabolized, as determined using doubly 

labeled water in free-living animals) indicate that 

the low water fluxes of air-breathing ectotherms 

(compared to endotherms) are primarily due to 

their low metabolic rates, rather than to 

supposedly more effective water economies. 

Desert ectotherms and endotherms have lower 

water fluxes and water economy index values than 

their nondesert relatives, reflecting the importance 

of physiological, behavioral, and morphological 

adaptations for achieving water balance in desert 

animals living under natural conditions. 

Nagy, K. A. and D. P. Costa. 1980. Water flux in 

animals: analysis of potential errors in the titrated water 

method. American Journal of Physiology 238:R454-

465. 

Laboratory studies indicate that titrated water 

measurements of water flux are accurate to within 

-7 to + 4% in mammals, but errors are larger in 

some reptiles. However, under conditions that can 
110 

occur in field studies, errors may be much greater. 

Influx of environmental water vapor via lungs and 

skin can cause errors exceeding ± 50% in some 

circumstances. If water flux rates in an animal 

vary through time, errors approach 15% in 

extreme situations, but are near ± 3% in more 

typical circumstances. Errors due to fractional 

evaporation of titrated water may approach ±9%. 

This error probably varies between species. Use of 

an inappropriate equation for calculating water 

flux from isotope data can cause errors exceeding 

±100%. The following sources of error are either 

negligible or avoidable: use of isotope dilution 

space as a measure of body water volume, loss of 

nonaqueous tritium bound to excreta, binding of 

tritium with nonaqueous substances in the body, 

radiation toxicity effects, and small analytical 

errors in isotope measurements. Water flux rates 

measured with titrated water may be expected to 

be within ±10% of actual flux rates in most 

situations. 

Robertshaw, D. 1982. Potential errors in the technique 

for estimating total body water and water turnover using 

titrated water. Pages 33-42 in Use of titrated water in 

studies of production and adaptations in ruminants. 

International Atomic Energy Agency, Vienna, Austria. 

If the assumption is made that the body is unable 

to differentiate between water and titrated water, 

the dilution of administered titrated water should 

give a measure of the total body water and its 

subsequent rate of dilution will measure total 

water intake, or output if the water pool size 

remains constant. In general, estimates of body 

water content from the dilution of titrated water 

overestimates body water measured directly by 

desiccation. Likewise, water turnover measured 

from the rate of dilution will be overestimated. 

The reasons for this error are not known but 

several factors may contribute. Loss of titrated 

water during equilibration will result in either an 

overestimate or underestimate of body water when 

water losses during equilibration are, respectively, 

greater or less than the specific activity of the 

final equilibration value. Incorporation of the 

isotope into non-aqueous compounds is thought to 

account for part of the error. Fractionation of 

titrated water in the water of evaporative water 

loss also induces an error and is due, in part, to the 

ability of the skin to selectively retain titrated 

water and, in part, to the lower vapor pressure of 

titrated water when compared to water. 

Fractionation of the isotope will lead to an 

underestimate of body water and water turnover 

rate. Evidence exists that there is an exchange of 

water from the air with that of the body at the skin 

and respiratory mucosal surfaces, and that the 

magnitude of the error is directly proportional to 

the ambient humidity. This is probably the major 

source of error. 

Speakman, J. R. 1997. Doubly labeled water: theory 

and practice. Chapman and Hall, London, United 

Kingdom. 399 p. 

This book reviews the energetics, theory, 

biochemical basis, isotope turnover in the body, 

assumptions for use, practice, methodology, and 

considerations, and analysis of the use of doubly 

labeled water in physiological research both in the 

laboratory and in field situations. 

General Desert Ecophysiology 

Adolph, E. F. 1947. Water metabolism. Annual Review 

of Physiology 9:381-408. 

The review summarizes published information on 

water metabolism from 1945 to 1946. 

Topics reviewed include water turnover, water 

excesses, dehydrations, water uptake, 

nonexcretory water loss, excretion of water, 

neurohypophyisis and water diuresis, and 

water content and redistributions. 

Chew, R. 1961. The water metabolism of desertinhabiting vertebrates. Biological Review 36:1-31. 

This review summarizes the water metabolism of 

desert-inhabiting vertebrates, including 

amphibians, reptiles, birds, and mammals. 

Behavioral adaptations, resistance to water loss 

and water uptake through the skin, kidney and 

bladder function, tolerance to dehydration and 

total physiological response of amphibians. 

Cutaneous and urine water loss and uricotelism 

and ureotelism are reviewed for reptiles. 
111 

Evaporative water loss, water balance, 

thermoregulation, drinking, kidney and cloaca 

function, and behavioral mechanisms of birds are 

also reviewed. For desert dwelling mammals, 

water intake, water loss, and kidney function are 

reviewed. 

McArthur, A. J. and J. A. Clark. 1988. Body temperature 

of homeotherms and the conservation of energy and 

water. Journal of Thermal Biology 13:9-13. 

This paper considers the reasons for the narrow 

range of body temperatures of homeotherms. 

Analysis of heat and water balance suggests that 

the observed range is consistent with the 

conservation of energy in the cold and water in 

heat. Poorly insulated “homeotherms” can 

economize on both water and energy needs if they 

accept a thermolabile body temperature. 

Schmidt-Nielsen, K. and B. Schmidt-Nielsen. 1952. 

Water metabolism of mammals. Physiological Review 

32:135-166. 

The physiological problems associated with 

obtaining enough water for normal functioning of 

the body and heat regulation are reviewed in 

desert mammals with emphasis on the kangaroo 

rats (Dipodomys spp.). Water balance, intake, and 

output in kangaroo rats are discussed including 

mechanisms associated with kidneys, and 

evaporation. The review also discusses mammals 

that do not use water for regulation of heat as well 

as those that regularly use water in heat 

regulation. The review of mammals that use water 

in heat regulation includes: man, dog, cattle, 

sheep, donkey, and the camel. 

Schmidt-Nielsen, B. and K. Schmidt-Nielsen. 1961. 

Structure and concentrating mechanism in the 

mammalian kidney. American Journal of Physiology 

200:1119-1124. 

In a number of mammalian kidneys a close 

correlation was found between renal medullary 

thickness and ability to concentrate electrolytes in 

the urine, indicating that both outer and inner zone 

of the medulla act as a countercurrent multiplier 

system. Further evidence for this assumption was 

furnished through studies of the distribution of 

urea and electrolytes in different kidney types 

during antidiuresis. The beaver with 100% shortlooped nephrons, the rabbit with 44% long-looped 

nephrons, and the desert rodent Psammomys with 

100% long-looped nephrons were studied. In all 3 

kidney types sodium and urea concentrations 

increased to approximately the same level in the 

outer zone of the medulla. In the rabbit and 

Psammomys kidneys a considerable increase in 

sodium concentration was found through the inner 

zone of the medulla. This can best be explained if 

we assume that the sodium pump, which has been 

demonstrated in the thick ascending limb of the 

loop of Henlé, functions in a similar manner in the 

thin limb. 

Yousef, M. K. 1971. Titrated water turnover rate in 

desert mammals. Pages 333-341 in A. A. Moghissi and 

M. W Carter, editors, Tritium. Messenger Graphics, 

Phoenix, Arizona, USA. 

Water turnover rates of large and small desert 

adapted mammals are compared using titrated 

water. Small mammals have faster water turnover 

rates in proportion to body mass. Relative 

proportions of body water content and body solids 

content are compared among large mammals. It is 

concluded that water turnover rates exhibit 

interspecific differences on the basis of water use 

for thermoregulation, reabsorption, and water loss 

through urine and feces.