298
ABSTRACTS
vaporization has a minimum of 2 kg. at 5° C. or
6°C. and increases slowly to about 2.5-4 kg. at
15°C., with a rapid increase to as much as 7 kg. at
21°C. and a slower further increase to an unknown
limit; these observations have, however, been con-
siderably influenced by the variable plane of nutri-
tion and coat cover of the subjects ; (4) Atmospheric
humidity; although theoretically high humidity
would be expected to depress vapourization, the
limited number of observations made suggested that
humidity has little effect.
When water lost by vaporization is plotted against
total heat emission the curve obtained is roughly
S-shaped, which is predictable also on theoretical
grounds.
Pulse and respiration rates are intimately connected
with the burden of heat disposal by radiation and
evaporation. Records of pulse and respiration
counts in several breeds of cows in relation to milk
production and summer and winter temperatures
show that both rates are capable of great change.
The data when properly interpreted indicate that
both pulse and respiration rates are higher in breeds
of higher average milk yields ; that high respiration
rate is not always associated with higher milk yield,
while higher pulse rate always is. Acceleration of
pulse rate allows dissipation of heat both by radiation
and evaporation whereas acceleration of respiration
helps heat emission by evaporation only. Hence in
high milk secretion, association of low respiration
with high pulse rate would be advantageous in
effecting economy of water for milk production.
Under tropical condition at 36°C., the average
respiration rate per minute of Holstein, cross-bred
and zebu are 107.0, 89.3 and 46.0 respectively. The
deterioraton of European cattle in the tropics is
obviously due to the failure of heat disposal by radia-
tion and the shift of the burden on to water evapora-
tion, resulting not only in the decline in milk yield
but also in the breakdown of constitution. Between
Holstein and zebu, although disposal of heat varies in
mode there appears to be no difference in the capacity
of heat emission. But such is not the case between
show and ordinary dairy cows. In a show cow
producing 3,000 gallons of milk in a lactation, the
heat emission by evaporation entails vaporization of
30-40 kg. of water which is almost double the amount
of an ordinary dairy cow. This large evaporation
seems to suggest important adaptation in respect of
pulse and respiration rates, such as high pulse and
low respiration count. Whatever be the nature of
the adaptation, it is only the type of cow, which is
capable of evaporating large amounts of water, that
is likely to maintain high production in the tropics.
Whether this would be true in practice or not, only
further experimentation can reveal. So far as
ordinary dairy cows are concerned, close shearing and
the provision of shade are the only practical expedi-
ents which can help in maintaining their milk pro-
duction in the tropics.
Since skin happens to be a medium from which
heat emission takes place by evaporation and
radiation, the factors
which
affect
skin
temperature have important significance. Skin tem-
perature rises with the rising plane of nutrition. It
is doubtful whether this is an advantage. In fatten-
ing steers, heat emission and skin temperature seem
to go in the reversed direction with the degree of
utilization of absorbed food. As exposure to sun
raises the skin temperature above that of the body
this should adversely affect the normal mode of heat
disposal.
When the outgo of water through various channels
enumerated above is reckoned against the intake of
both performed and potential water in feeds, a
satisfactory balance can be obtained. A proper
knowledge of various channels of outgo under varied
dietetic and environmental conditions should thus
help in evaluating the water requirement.
The water consumption of sheep, like that of the
cow, varies with the type of ration, plane of nutrition
and external temperature. Pregnancy seems to
impose higher water requirements. Grazing on
fresh pastures may cut the water requirement to nil.
On the average, the requirement is 2 litres water per
kg. dry food consumed.
The recorded data on water requirement of the
horse are meagre. By one estimate, it is 2-3 litres
of water per kg. dry food consumed. The other
estimate gives 35-45 litres daily.
For the growing pig, a water to dry feed ratio of
3 : 1 is considered satisfactory ; at bacon weight,
however, the ratio is narrowed. The consumption of
water by farrowing sows is slightly greater at higher
external temperature. The water requirement of
pregnant and lactating sows has been calculated to
be 8-12 lb. and 40-50 lb. per day respectively.
The water consumption of poultry varies with live
weight, external temperature and egg-production.
In Leghorn hens in lay, the water requirement has
been calculated at 250 gm. daily. A few observa-
tions on water loss in vaporization have been made
on fowls, which seem to agree generally with those
recorded on cattle. [ S. C. R.]
The semen of animals and its use for artificial
insemination. JAMES ANDERSON (1945). Tech-
nical Communication Imperial Bureau of Animal
Breeding and Genetics, Edinburgh
ARTIFICIAL insemination has aroused wide interest in
recent years on account of its enormous possibilities
in the development and improvement of livestock
production. Since the publication by the Imperial
Bureau of Animal Breeding and Genetics, in 1933, of
a review on artificial insemination by Dr Arthur
Walton, a voluminous literature has accumulated on