# Effect of Feed Restriction during Pregnancy on Performance and Productivity of New Zealand White Rabbit Does

Authors: Abeer Nafeaa; Souad Abd Elfattah Ahmed; Said Fat Hallah
Journal: Veterinary Medicine International
 (2011)

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## Abstract

This study aimed to evaluate effect of stage of feed restriction on performance and productivity of pregnant does. New Zealand white female rabbits were randomly divided into three groups. Control group was provided daily with 185 g of food increased to 200 g from the 15th day of gestation.R1 was offered daily a restricted amount of food (60% restriction, 111 g) for the first half of pregnancy and then offered 200 g of food daily till parturition. R2 was provided  with  185 g of food daily through the first half of pregnancy and then offered daily a restricted amount of food (60% restriction, 120 g) for the second half. After parturition, food was provided adlibitum. Maternal body weights, litter size, litter weight, and average body weight of kits at kindling of R1 showed no change, whereas R2 showed significant reduction in the weights of does at the 4th week of pregnancy and at kindling. The birth weight and weaning weight of R2 were significantly reduced. The highest mortality was recorded in kits of R2. No significant differences in blood parameters or serum prolactin were observed. The serum protein was significantly reduced R2.


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## Body

## 1. Introduction

It is a common practice in commercial rabbit production to feed rabbit does to appetite directly after mating and during gestation. The young does fedad  libitum with diets of high energy level often show parturition problems, with the subsequent reduction of the number of newborn  rabbits, linked to excessive fatness [1]. In order to reduce the excessive fatness of young does, restricted feeding during pregnancy is frequently applied to obtain uniformity in their body weights, to avoid fattening and high mortalities around parturition [2], to increase voluntary intake at the beginning of the lactation period, and to allow a long productive life [3]. Also, feed restriction could be exploited in the feeding regimen of rabbits, especially in periods of inadequate supply of concentrates and forages [4]. But, feed restriction for rabbits has to be considered as a stress condition and applied with attention when other stressors occur [5].It is well known that fetal growth is dependent on an adequate supply of oxygen and nutrients crossing the placenta from the mother [6]. Moreover, nutrient supply to embryos and fetuses is exclusively dependent upon the mother [7]. Consequently, as the body size of the does decreases, the litter weight at kindling also reduces [8]. Furthermore, reduction of total caloric intake during pregnancy, eating disorders, and related indicators such as low pregnancy weights of does account for a significant proportion of intrauterine growth retardation [9]. Moreover, factors that perturb fetal substrate supply and are known to be responsible for much fetal growth restriction, such as placental insufficiency or poor maternal nutrition, are implicated in the long-term programming of adult dysfunction and disease [10].  Previous studies concluded that,  after  the  restoration of maternal nutrition over  the second half of gestation, fetal adipose tissue development  is enhanced, which may act to place these individuals  at  increased  risk  of  obesity  in  later  life  [11]. However, details of the influence of restricted feeding of the pregnant does on their blood parameters shortly after parturition and on the performance of their offspring are still obscure.So, the aim of this work is to evaluate the effect of the stage of feed restriction during  pregnancy  on  maternal  body  weights,  weights  of  offspring  at  birth  and weaning as well as  some  hematological and biochemical parameters of the young  does.


## 2. Materials and Methods

### 2.1. Experimental Design

New Zealand white female rabbits (sixty females) of 20 weeks of age (first kindling) and weighed2800±100g were randomly divided into three equal groups: Group 1 (control group): rabbits were provided daily with 185 g of food increased to 200 g from the 15th day of gestation (daily food intake of pregnant does according to [12]); Group 2(R1, early feed restriction): rabbits were offered daily a restricted amount of food (60% restriction, 111 g) for the first half of pregnancy (the first fifteen days) and then  offered  200 g  of  food  daily  till  parturition;  Group  3(R2, late  feed restriction) : rabbits were provided with 185 g of food daily through the first half of pregnancy and  then offered daily a restricted amount of food (60% restriction, 120 g) for the  second  half  of  pregnancy.   Treatments started after natural mating.  After parturition, all does and their young were provided ad libitumamount of feed till weaning.  Rabbits  were  reared  in individual cages (50 cm ×  50 cm × 30 cm)  of galvanized wire net, equipped with an automatic drinker and a manual feeder. Rabbits were provided with a commercial pellet diet, containing 18% crude protein and 2700 Kcal/Kg ration metabolizable energy (ME).  Does  were  submitted  to  a  16-hour photoperiod  daily  and  the  minimum  ambient  temperature  was  set  at  18 ±  2°C. Fourteen days after mating, does were palpated to check pregnancy and nonpregnant does were excluded from the experiment.  Five days before kindling, does were provided an access to nest boxes that were attached to each cage. Does were weighed individually  at  the  start  of  the  experiment  then  every  two  weeks  and  just  after kindling. After kindling, the nest boxes were checked for live and still born kits. For each doe, the living kits were weighed to obtain the total litter weight at birth which were then divided by the number of kits (litter size at birth) to calculate the mean kits weight at birth. Then kits were weighed at 21 days of age and at the day of weaning (the 30th day). Kit’s mortality rate % was recorded for each group from birth till weaning.


### 2.2. Blood Collection

Blood samples were collected from does five days after kindling [13]. The blood samples were collected in the morning (10.00 a.m.) from the ear veins. Two blood samples were taken from each female: one sample was taken into a tube containing EDTA for determination of the hematological parameters and the other was taken without an anticoagulant, centrifuged at 3000 g, and then the serum was collected and stored at −20°C until assayed for prolactin hormone and the total protein concentration.


### 2.3. Hematological and Biochemical Analysis

Packed  cell  volume  (PCV),  red  blood  cell  number  (RBCs), and  hemoglobin concentration  (Hb) were determined using Wintrobe’s microhematocrite, improved Neubauer   hemocytometer,  and cyanomethemoglobin method, respectively. The erythrocytic indices, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC) were calculated according to [14]. Determination of serum prolactin was done according to [15] while determination of total protein concentration was done according to [16].


### 2.4. Statistical Analysis

Data collected were subjected to one-way ANOVA. Differences among means were tested by Duncan’s multiple range test.


## 2.1. Experimental Design

New Zealand white female rabbits (sixty females) of 20 weeks of age (first kindling) and weighed2800±100g were randomly divided into three equal groups: Group 1 (control group): rabbits were provided daily with 185 g of food increased to 200 g from the 15th day of gestation (daily food intake of pregnant does according to [12]); Group 2(R1, early feed restriction): rabbits were offered daily a restricted amount of food (60% restriction, 111 g) for the first half of pregnancy (the first fifteen days) and then  offered  200 g  of  food  daily  till  parturition;  Group  3(R2, late  feed restriction) : rabbits were provided with 185 g of food daily through the first half of pregnancy and  then offered daily a restricted amount of food (60% restriction, 120 g) for the  second  half  of  pregnancy.   Treatments started after natural mating.  After parturition, all does and their young were provided ad libitumamount of feed till weaning.  Rabbits  were  reared  in individual cages (50 cm ×  50 cm × 30 cm)  of galvanized wire net, equipped with an automatic drinker and a manual feeder. Rabbits were provided with a commercial pellet diet, containing 18% crude protein and 2700 Kcal/Kg ration metabolizable energy (ME).  Does  were  submitted  to  a  16-hour photoperiod  daily  and  the  minimum  ambient  temperature  was  set  at  18 ±  2°C. Fourteen days after mating, does were palpated to check pregnancy and nonpregnant does were excluded from the experiment.  Five days before kindling, does were provided an access to nest boxes that were attached to each cage. Does were weighed individually  at  the  start  of  the  experiment  then  every  two  weeks  and  just  after kindling. After kindling, the nest boxes were checked for live and still born kits. For each doe, the living kits were weighed to obtain the total litter weight at birth which were then divided by the number of kits (litter size at birth) to calculate the mean kits weight at birth. Then kits were weighed at 21 days of age and at the day of weaning (the 30th day). Kit’s mortality rate % was recorded for each group from birth till weaning.


## 2.2. Blood Collection

Blood samples were collected from does five days after kindling [13]. The blood samples were collected in the morning (10.00 a.m.) from the ear veins. Two blood samples were taken from each female: one sample was taken into a tube containing EDTA for determination of the hematological parameters and the other was taken without an anticoagulant, centrifuged at 3000 g, and then the serum was collected and stored at −20°C until assayed for prolactin hormone and the total protein concentration.


## 2.3. Hematological and Biochemical Analysis

Packed  cell  volume  (PCV),  red  blood  cell  number  (RBCs), and  hemoglobin concentration  (Hb) were determined using Wintrobe’s microhematocrite, improved Neubauer   hemocytometer,  and cyanomethemoglobin method, respectively. The erythrocytic indices, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC) were calculated according to [14]. Determination of serum prolactin was done according to [15] while determination of total protein concentration was done according to [16].


## 2.4. Statistical Analysis

Data collected were subjected to one-way ANOVA. Differences among means were tested by Duncan’s multiple range test.


## 3. Results and Discussion

Results of the effect of the stage of feed restriction during pregnancy on maternal body weights were presented in Table1.  Feed  restriction  during  the  first  half  of gestation did not affect the maternal body weights, whereas feed restriction during the second half of gestation was accompanied with significant reduction in the weights of does  at  the  4th week  of  pregnancy  and  at  kindling.  This decrease became nonsignificant from the second week after kindling till the end of the experiment. Similar results were recorded by many investigations which found that dams lost a significant amount of body weights throughout the gestation period as a result of undernutrition, but they were able to catch up to the ad libitumgroup by day 10 postnatal [17]. Other research recorded that, after delivery, the control group exhibited higher body weight than the restricted does, but at time of weaning all the mothers had similar live weights [13]. The results of the present study could be attributed to that as the postmiddle period of pregnancy is vulnerable to effects of reduced food consumption in pregnant rabbits [18], food-restricted females mobilized body fat and  reduced their energy  expenditure  for  maintenance  and  activity  especially  when  feed  restriction occurred shortly  before parturition [19]. That could be the cause of the significant reduction observed in the weights  of does subjected to feed restriction during the second  half  of  gestation  from the  4th week  of  pregnancy till  the  kindling.  After kindling, these does were provided ad libitumamount of feed and they were able to catch up to the control group by the 15th day of delivery. That could be because, the animal  under  quantitative  and  qualitative  feed  restriction  exhibited  compensative growth  as a consequence of increased food  intake  after  restricted  feeding  [13]. Consequently, when food was provided ad libitumto the previously restricted does, weight gain was significantly higher than that in the ad libitumgroup [11, 20].Table 1
The effect of the stage of feed restriction during pregnancy on maternal body weights (means ± SE).
ParameterGroupControlR1R2Weight  of  does  at  the start (g)2860.00 ± 77.67a2790.00 ± 165.63a2873.33 ± 38.44aWeight of  does after two weeks (g)3216.67 ± 72.65a2966.67 ± 130.17a3100.00 ± 76.38aWeight   of   does   after four weeks (g)3500.00 ± 57.74a3443.33 ± 34.80a3196.67 ±  68.88bWeight ofdoes at kindling day (g)3140.00 ± 66.58a3083.33 ± 95.28a2783.33 ± 70.55bWeight of does after  six weeks (g)3540.00 ± 95.39a3490.00 ± 66.58a3480.00 ± 58.59aWeight   of   does   after  eight weeks (g)3593.33 ± 63.59a3556.67 ± 177.42a3540.00 ± 63.51aa, bMeans with the different superscripts in the same raw are significantly different (P≤0.05).R1:  early feed restriction.R2:  late feed restriction.The present study revealed that feeding level during gestation period did not affect the litter size at birth (Table2). There were no abortions, external, visceral, or skeletal malformations associated with any of the levels of maternal body weight loss due to feed restriction. Similar results were obtained in rabbits [21] and in rats [17]. However,  previous  studies  investigated  the  effect   of   feeding  level  during  first gestation in  young  does  on  reproductive  performance and recorded  a  reduced number of live born kits as a result of low-feeding level during early gestation [22] and the litter size increased with increased weight of does [23, 24]. Also, feed restriction of  pregnant  does  resulted  in  developmental  abnormalities  expressed  by  abortion, reduced fetal weight, and alterations in ossification [25]. One potential explanation for the results of the present study is that the young rabbit does could maintain normal blood supply to their embryos during this feeding restriction level as indicated by the hematological results which revealed no changes in hematological parameters due to feed restriction (Table 3).Table 2
The  effect  of  the  stage  of  feed  restriction  during  pregnancy  on  litter  performance (means ± SE).
ParameterGroupControlR1R2Litter Size at birth6.00 ± 0.58a5.67 ± 0.33a5.00 ± 0.58aTotal litter weight at birth (g)304.17 ± 8.21a320.00 ± 17.32a236.67 ± 8.82bMean kit  weight at birth (g)51.57 ± 4.60a57.22 ± 6.55a48.22 ± 3.86aMean kit  weight at the 21st   day (g)380.00 ± 11.55b446.67 ± 8.82a308.33 ± 11.67cIndividual weaning body weight (g)471.67 ± 14.81b558.33 ± 16.19a411.67 ± 7.26cMortality rate %4.33 ± 0.67a3.33 ± 0.88a7.00 ± 0.58ba, b, c Means with the different superscripts in the same raw are significantly different  (P≤0.05).R1:  early feed restriction.R2:  late feed restriction.Table 3
The effect of the stage of feed restriction during pregnancy on hematological findings of does at the 5th day post partum (means ± SE).
ParameterGroupControlR1R2RBCs (106/μl)3.64 ± 0.27a3.76 ± 0.32a3.33 ± 0.15aPCV (%)30.65 ± 0.62a29.26 ± 0.59a28.34 ± 0.75aHb (g/dl)9.14 ± 0.54a9.24 ± 0.39a8.31 ± 0.41aMCV (fl)84.79 ± 4.52a78.61 ± 5.21a85.39 ± 2.17aMCH (pg)25.15 ± 0.64a24.74 ± 1.19a24.98 ± 0.12aMCHC (%)29.79 ± 1.36a31.59 ± 1.29a29.30 ± 0.86aProlactin3.85 ± 0.15a4.20 ± 0.15a3.51 ± 0.29aTotal protein (g/dl)5.63 ± 0.15a5.90 ± 0.26a4.92 ± 0.16ba, bMeans with the different superscripts in the same raw are significantly different (P≤0.05).R1:  early feed restriction.R2:  late feed restriction.In the present investigation it was clear that feed restriction during the first half of gestation increased the litter weight at birth and the mean kit weights from birth till weaning as compared to the control group but the differences were nonsignificant at any experimental periods (Table2). These results disagree with the result obtained by a previous study which recorded a significant decrease in  the weights of fetuses carried  by  does  subjected  to  different  degrees  of  feed  restriction  maintained  for various periods during gestation [26, 27]. The obtained results could be ascertained by that, in the first and second weeks after feed restriction, compensatory feed intake occurred and does which ate more than average during the last week of gestation had heavier kits than does eating less than average feed intake [21], and in most instances, the energy level of the diet fed to the does influenced birth weight (higher energy level, greater weight) [2].On  the  other  hand,  feed  restriction  during  the  second  half  of  gestation significantly decreased the litter weight at birth as well as the postnatal pup weights; however, the differences  were  significant only from the 21th day till weaning (Table2).  Similar  results  were  obtained  by some  previous  studies  which  recorded  that offsprings  from  undernourished  group  were  significantly smaller  at  birth and  were significantly  less  active  at  all  ages  independent  of  postnatal  nutrition  [28].  The reduced litter weight at birth of R2   in the  present study could be attributed to the significantly reduced total protein concentration measured in  the serum of the does (Table 3) where it is well known that the maternal body composition and  diet  are thought to affect the fetal development as a result of both direct effects on substrate availability to  the  fetus  and  indirectly through changes  in placental functions  and structure [29].  Furthermore, it was recorded that birth weight of rabbit kits was correlated with daily weight gain and weight at weaning [30]. So the reduction observed in mean kit weights of R2 from birth till weaning could be attributed to the reduced birth weight not to the amount of milk intake (no-significant differences were recorded between control and feed-restricted does in serum prolactin concentrations (Table 3).As regarding the mortality rate % among the offspring from birth till weaning, the pups of feed-restricted does during the second half of gestation showed a significantly higher mortality rate % than the kits of the control does and feed-restricted does during the second half of gestation period (Table2). The result disagreed with the result recorded in a previous research [13] which recorded similar number of rabbits at weaning as well as similar mortality rates for all groups (kits of control does and kits of does under different nutritive levels).  The result recorded in the present study could be attributed to the significantly reduced litter weight (236.67±8.82g) as well as the reduced kit weight (48.22±3.86g) of R2  at birth, whereas within any given rabbit breed there is a close correlation between the weight of offspring at birth and their viability [18]. Furthermore, a previous study [31] concluded that, in the medium-sized  breeds  (including  New  Zealand  white  rabbits),  the  minimum  birth  weight consistent with  the  survival was between 40 and 45 g which was very close to the birth weight of R2  in the present study.The blood parameters and serum prolactin concentrations of the does at the 5th day post partum were shown in Table3; there were no significant differences in RBCs, Hb, PCV, MCV, MCH, or  MCHC values between the control and feed-restricted groups. The obtained results agreed with the results obtained by [32] who concluded that hematological examination of pregnant does revealed variations in several blood parameters only in animals subjected to restricted feeding at 20 g/head/day when blood samples were collected on gestation day 19. Also, there were no significant differences recorded in serum prolactin concentrations between the control and feed-restricted groups.  Similar results were obtained in rat [33], in ewes [11], and in mare [34], whereas, a previous study recorded some specific changes in the endocrine status during food restriction depending on the severity of food restriction and its duration [35].Feed restriction during the first half of gestation did not affect the serum protein level  whereas   feed  restriction  during  the  second  half  of  gestation  significantly decreased  the  total protein  as  compared  with  the  control group  and  this  finding reflected low nutritive conditions due to  restricted feeding as previously reported by [32, 36]. The significantly reduced total protein concentrations measured in serum of feed  restricted  does  at  the  second  half  of  gestation  could  be  the  cause  of  the significantly reduced weights of their litters at birth.


## 4. Conclusion

In order to reduce the excessive fatness of young rabbit does, restricted feeding during  the  first  half  (the  first  two  weeks)  of  gestation  is  recommended  as  feed restriction for 15 days during early gestation does not affect the performance of young does, which had been fed to appetite during rearing.



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*Source: 839737-2011-09-04.xml*