Indian J. Anim. Res., 40 (1): 9-14, 2006 GENETIC AND NON GENETIC FACTORS AFFECTING THE LITTER TRAITS OF BROILER RABBITS* B. Ekambaram, V. Prabhakar Rao, A. Sreerama Murthy 1, A. Satyanarayana 2 and B. Ramesh Gupta Department of Animal Genetics and Breeding, College of Veterinary Science, Rajendranagar, Hyderabad - 500 030, India ABSTRACT The data on pre-weaning and post weaning litter weights and litter size at birth and weaning age of 4 weeks of 512 bunnies born in 109 kindlings of New Zealand White (NN), Soviet Chinchilla (SS), Grey Giant (GG) and Flemish Giant (FF) were analyzed. Genetic group had significant effect on litter weights at 1, 2, 3, 8, 10 and 12 weeks of age. Litter size influenced the pre-weaning and post weaning litter weights significantly, while the month of birth affected the litter weights of bunnies from 3 to 12 weeks of age. The effect of sex of bunny was not significant. The milk yield up to 18 days in NN, SS, GG and FF does averaged 1267.34±23.78, 1043.67±23.95, 1534.34±56.34 and 1423.67±118.44 g, respectively. The phenotypic correlations among the pre-weaning and post weaning litter weights were positive and ranged from moderate to high in magnitude. The R 2 - values of the multiple regression equations developed to predict the weaning weight of bunnies based on the litter size at birth, milk yield during first week of lactation and dam weight of kindling ranged from 58 to 72 per cent. INTRODUCTION The litter traits such as the litter size and litter weights in litter bearing animals like rabbits are important economic traits in profitable broiler rabbit rearing. The preweaning litter weights reflect the doe s productivity, which in turn depends upon the nursing ability and milking capacity of the doe. The total market weight of the litter is strongly correlated with the milk production potential of the doe. Therefore, the present investigation was undertaken to study the influence of genetic and non-genetic factors on the preweaning and post weaning litter traits of New Zealand White (NN), Soviet Chinchilla (SS), Grey Giant (GG) and Flemish Giant (FF) rabbits reared under farm conditions. MATERIAL AND METHODS The data on pre-weaning (at birth, 1, 2, 3 and 4 weeks of age) and post weaning (at 6, 8, 10 and 12 weeks of age) litter weights and litter size at birth and weaning (4 weeks of age) of 512 bunnies born in 109 kindlings of NN (37), SS (29), GG (29) and FF (14) in the Rabbit Production for Meat Scheme, from February 1996 to September 1996 were utilized in the present study. The bunnies were reared in iron mesh cages along with their dams from birth to 4 weeks of age and then the weaning was done by separating the young ones from their mothers. At weaning, the bunnies were sexed, ear-tagged and reared in groups of six, in the cages having a floor space of six square foot. The milk yield of a sample of 3 does from each of the four breeds was recorded from kindling to 18 days of lactation. The milk yield was measured as the difference in body weight of the bunnies before and after suckling their mothers for about 5 minutes, once in the morning and in evening. After suckling, these bunnies were maintained in the nest boxes away from the does cages. The influence of genetic group, litter size at birth and weaning, month of birth and regression * Part of M.V.Sc. Thesis of the first author submitted to the Acharya N G Ranga Agricultural University, Hyderabad. Present address: 1 Principal Scientist (Retd.), AICRP on Poultry Breeding, Rajendranagar, Hyderabad 500 030. 2 University Computer Centre, Acharya N G Ranga Agricultural University, Rajendranagar, Hyderabad 500 030.
10 INDIAN JOURNAL OF ANIMAL RESEARCH of litter weights on dams weight at kindling on the pre-weaning litter weights and the influence of genetic group, litter size birth and weaning, month of birth and sex of bunny on post weaning litter weights were studied by employing the least squares technique (Harvey, 1979). The phenotypic correlations were estimated within the genetic group based on the data adjusted for the effects of litter size at birth, month of kindling and sex of bunny. RESULTS AND DISCUSSION The least squares means (g) according to the genetic groups, litter size and sex for the pre-weaning and post weaning litter weights are presented in Tables 1 and 2, respectively. The least squares analysis of variance has revealed that the genetic group of bunny had significantly affected the litter weight at 1, 2, 3, 8, 10 and 12 weeks of age, which reflected the differential milking capacity and mothering ability of the does belonging to different genetic groups. Significant effect of genetic groups on litter weights was also reported by Krogmeier and Dzapo (1991) in New Zealand White and their crosses, while Kosko (1979) observed non-significant effect of genetic group on litter weights in purebred and crossbred rabbits. The litters of GG genetic group were the heaviest from birth to 8 weeks of age and those of FF were the highest at 10 and 12 weeks of age. The litter weights of NN and SS breeds, which were lower at preweaning period continued to have lower litter weights in the post weaning period. The effect of litter size at birth was significant (P<0.01) on litter weights at all the pre-weaning ages studied, whereas the litter size at weaning significantly (P<0.01) influenced the litter weights throughout the post-weaning period. Significant effect of litter size on litter weights was also observed in NN rabbits (El-Sheikh and El-Bayomi, 1994) and 3-way cross broiler rabbits (Reddy et al. 2003). The least squares means of pre-weaning and post weaning litter weights increased with the increase of the litter size at birth and litter size at weaning, respectively. A similar trend in the pre-weaning litter weights was reported by Reddy et al. (2000). The results of least squares analysis of variance indicated that the month of birth of bunnies affected the litter weights during later stages (3 and 4 weeks of age) and through out the post weaning period, which was in agreement with the reports made on NN bunnies by Mc Nitt and Moody (1990) and in Californian rabbits by Poornima et al. (2002). Bunnies born in March attained the highest litter weights at 3 and 4 weeks of age, while those born in the month of June had the highest litter weights from 8 to 12 weeks of age. These findings were similar to the report of Ayyat et al. (1995). The effect of regression of preweaning litter weight on the does weight at kindling was positive and significant at one week age only, which indicated the possibility of attaining higher litter weights at one week age by improving the weight of the does at kindling. The influence of sex of bunny on post weaning litter weights was not significant throughout the post weaning period (Table 2), which indicated that males had no significant advantage over the females in their post weaning litter weights and sex of bunny need not be considered as a source of variation in the selection programmes aiming to improve the post weaning litter weights in broiler rabbits. The overall mean lactation milk yield of the does up to 18 days of lactation was 1317.25±62.60 g with the mean milk yields of 1267.34±23.78, 1043.67±23.95, 1534.34±56.34 and 1423.67±118.44 g in NN, SS, GG and FF genetic groups,
Vol. 40, No. 1, 2006 11 Table 1. Least squares means of pre-weaning litter weights (g) of broiler rabbits n Birth 1 week 2 weeks 3 weeks 4 weeks Mean SE Mean SE Mean SE Mean SE Mean SE Overall 109 196.31 6.08 273.97 12.49 593.74 17.82 1034.81 25.35 1520.00 39.07 Genetic group New Zealand White 37 183.80 6.04 242.70 b 12.41 546.27 c 17.72 958.23 b 25.20 1453.33 38.82 Soviet Chinchilla 29 189.21 6.08 244.20 b 12.50 562.35 b 17.83 980.09 b 25.35 1464.47 39.07 Grey Giant 29 195.82 6.06 316.84 a 12.45 649.55 a 17.78 1123.95 a 25.28 1600.34 38.96 Flemish Giant 14 216.43 14.21 292.24 ab 29.20 616.81 ab 41.68 1076.97 ab 59.26 1561.86 91.34 Litter size at birth Up to 3 bunnies 26 88.47 c 6.06 83.07 c 12.46 346.15 c 17.79 731.98 c 25.30 1099.13 c 38.98 4 to 6 bunnies 68 196.31 b 6.01 294.09 b 12.34 605.33 b 17.62 1020.05 b 25.05 1485.52 b 38.62 >6 bunnies 15 304.17 a 13.14 444.75 a 26.99 829.75 a 35.83 1352.40 a 54.80 1975.34 a 84.45 Month of birth February 8 212.27 6.27 271.30 12.88 562.73 18.40 981.90 b 26.15 1374.71 b 40.31 March 8 214.39 6.36 311.40 13.08 651.16 18.67 1149.85 a 26.55 1709.38 a 40.91 April 10 183.91 5.99 248.22 12.32 524.10 17.58 905.91 c 25.00 1385.75 b 38.53 May 13 172.28 5.98 249.09 12.30 547.91 17.56 972.33 b 24.97 1444.45 b 38.50 June 29 178.00 5.98 270.12 12.28 621.88 17.53 1135.20 a 24.93 1612.81 a 38.43 July 21 210.32 5.96 266.31 12.24 638.94 17.47 1075.03 ab 24.85 1640.57 a 38.30 August 5 216.52 6.81 309.47 14.05 624.36 20.06 1113.31 a 28.52 1601.42 ab 43.95 September 15 182.83 12.36 265.86 25.40 578.95 36.24 944.94 bc 51.54 1390.88 b 79.43 Regression on dam 0.027 0.082 0.058 0.018 0.016 weight at kindling Means with same superscript(s) do not differ significantly (P<0.05); n = number of kindlings. Table 2. Least squares means of post weaning litter weights (g) of broiler rabbits n 6 weeks 8 weeks 10 weeks 12 weeks Mean SE Mean SE Mean SE Mean SE Overall 76 2400.41 67.14 3272.43 96.23 4043.81 106.55 5092.09 141.04 Genetic group New Zealand White 24 2340.82 103.76 3062.91 bc 148.82 3839.46 b 164.67 4970.73 b 217.96 Soviet Chinchilla 24 2217.63 101.67 3007.95 c 145.72 3620.40 b 161.35 4429.54 c 213.57 Grey Giant 16 2532.51 116.76 3558.94 a 167.35 4303.42 a 185.29 5324.29 a 245.26 Flemish Giant 12 2510.70 127.56 3459.93 ab 182.83 4411.96 a 202.43 5643.80 a 267.95 Litter size at weaning Up to 3 bunnies 30 1608.30 c 81.87 2124.46 c 117.35 2663.75 c 129.93 3263.14 c 171.98 4 to 6 bunnies 35 2508.21 b 83.65 3375.93 b 119.90 4091.73 b 132.74 5068.46 b 175.71 >6 bunnies 11 3084.73 a 142.40 4316.91 a 204.10 5375.96 a 225.98 6944.66 a 299.12 Month of birth February 5 1783.71 c 199.31 2511.58 c 285.67 3243.19 d 316.30 4285.25 c 418.67 March 5 2182.73 b 197.91 2908.08 c 283.66 3525.79 cd 314.06 4791.07 c 415.72 April 9 2784.93 a 147.23 3789.77 ab 211.02 4520.89 ab 233.64 5647.96 ab 309.26 May 13 2466.59 b 127.53 3515.53 b 182.80 4246.04 b 202.39 4951.06 c 267.90 June 27 2705.24 a 85.03 3850.24 a 121.88 4674.52 a 134.94 5766.76 a 178.62 July 17 2479.28 ab 109.41 3059.40 c 156.82 4052.44 bc 173.63 5110.44 bc 229.83 Sex of bunny Male 36 3423.75 88.73 3382.43 127.17 4168.07 140.80 5217.60 186.37 Female 40 2377.10 80.94 3162.43 116.01 3919.54 128.44 4966.58 170.02 Means with same superscript(s) do not differ significantly (P<0.05); n = number of kindlings.
12 INDIAN JOURNAL OF ANIMAL RESEARCH Table 3. Estimates of phenotypie correlations ainong the litter weights at various pre-weaning and post-weaning ages and milk production and associative traits Birth Genetic Group 1 week 2 weeks 3 weeks 4 weeks LSB (a) Pre-weaning litter weights New Zealand White 0.42** 0.33** 0.22 0.23 0.43** Soviet Chinchilla 0.39* 0.39* 0.42* 0.39* 0.46** Grey Giant 0.41* 0.32 0.29 0.27 0.43* Flemish Giant 0.48* 0.46 0.42 0.31 0.44 1 week New Zealand White 0.36** 0.27 0.25 0.37* Soviet Chinchilla 0.41** 0.41* 0.39* 0.41* Grey Giant 0.42* 0.35* 0.34* 0.36* Flemish Giant 0.48* 0.42 0.33 0.45 2 weeks New Zealand White 0.43** 0.41** 0.37* Soviet Chinchilla 0.45** 0.42* 0.42* Grey Giant 0.43* 0.38* 0.29 Flemish Giant 0.46 0.36 0.45 3 weeks New Zealand White 0.44** 0.28 Soviet Chinchilla 0.43* 0.45** Grey Giant 0.44** 0.28 Flemish Giant 0.42 0.44 4 weeks New Zealand White 0.31* Soviet Chinchilla 0.42* Grey Giant 0.32 Flemish Giant 0.38 8 weeks 10 weeks 12 weeks LSW (b) Post weaning litter weights 6 weeks New Zealand White 0.48** 0.48** 0.47* 0.42* Soviet Chinchilia 0.48** 0.46* 0.38* 0.45* Grey Giant 0.48* 0.48* 0.47* 0.42 Flemish Giant 0.47 0.47 0.45 0.45 8 weeks New Zealand White 0.49** 0.48* 0.40* Soviet Chinchilla 0.49** 0.42* 0.45* Grey Giant 0.49* 0.48* 0.41* Flemish Giant 0.48 0.48 0.45 10 weeks New Zealand White 0.49** 0.42 Soviet Chinchilla 0.44* 0.46* Grey Giant 0.49* 0.44 Flemish Giant 0.48 0.46 12 weeks New Zealand White 0.45* Soviet Chinchilla 0.45* Grey Giant 0.45 Flemish Giant 0.45 LSB MY1 MY2 TMY (c) Milk production and associative traits D W K -0.23 0.27-0.11 0.08 LSB 0.06 0.48 0.30 MY1 0.58* 0.89** MY2 0.58* Significant at P<0.05; ** - Significant at P<0.01; LSB = Litter size at birth; LSW = Litter size at weaning; DWK = Dams weight at kindling; MY 1 = Milk yield during 1 st week of lactation; MY2 = Milk yield during 2 nd week of lactation; TMY = Total milk yield.
respectively, which were higher than the mean milk yield of 600 g reported by Singh (1996). In the present study, the phenotypic correlation between the doe weight at kindling and total milk yield was low (0.08) and not significant, as similar to the report of Lukefahr et al. (1983) made on New Zealand White rabbits. However, Mc Nitt and Lukefahr (1990) reported higher value (0.343) and Singh (1996) reported significant correlation of milk yield with does weight at kindling. The litter size at birth had positive correlation with total milk production of the doe (0.30), in first week (0.06) and second week (0.48) after kindling, which were comparable with the report of Lukefahr et al. (1983). Mc Nitt and Lukefahr (1990), however, reported higher correlation coefficients than Vol. 40, No. 1, 2006 13 those obtained in the present study. The higher milk production in the does with larger litters might be due to a greater tactile stimulation of the teats of does by the bunnies enhancing the milk secretion. The higher suckling intensity by the larger litters might also led to higher release of oxytocin (Hafez, 2000) resulting in complete evacuation of residual milk. The phenotypic correlations among the milk yields during first and second week and total milk yield were significant and high. The step-up multiple regression equations developed to predict the weaning weight (Y) of bunnies at 4 weeks of age, based on the litter size at birth (X 1 ), milk yield during first week of lactation (X 2 ) and dam weight of kindling (X 3 ) were: Y = 503.60-35.90 X 1 (R 2 = 58%) Y = 393.82-36.84 X 1 + 0.21 X 2 (R 2 = 68%) and Y = 290.08-34.38 X 1 + 0.17 X 2 + 0.04 X 3 (R 2 = 72%) In the prediction equations, inclusion of the milk yield in second week of lactation (X 2 ) and dam weight at kindling (X 3 ), in addition to the litter size at birth (X 1 ) did not improve the R 2 -values substantially. However, these three variables together contributed 72% of the variation in weaning weight of bunnies. The estimates of phenotypic correlations among the litter weights during pre-weaning and post weaning ages are presented in Table 3. All the correlation coefficients were positive in four genetic groups studied and the estimates ranged from moderate to high during pre-weaning (0.22 to 0.48) and post weaning (0.38 to 0.49) period. The results revealed that the litter weights of the bunnies at early age were the reliable indicators of the litter weights at later age and selection of bunnies for higher litter weights during early age would automatically improve the same at later ages. The litter size at birth had significant and positive correlations with litter weights at pre-weaning ages, ranging from 0.28 to 0.46 among the four breeds, whereas the phenotypic correlations between litter size at weaning and post weaning litter weights were positive and high, ranging from 0.41 to 0.46. This revealed that the selection goals to improve the litter weights might be attained by the improvement of litter size at birth and weaning. REFERENCES Ayyat, M.S. et al. (1995). World Rabbit Sci., 3: 119-124. El-Sheikh, A.I. and El-Bayomi, K.M. (1994). Anim. Breed. Abstr., 63: 1303. Hafez, E.S.E. (2000). Reproduction in Farm Animals. 6 th Ed. Harvey, W.R. (1979). Least Squares Analysis of Data with Unequal Subclass Numbers, USDA, Agricultural Research Service, USA.
14 INDIAN JOURNAL OF ANIMAL RESEARCH Kosko, I. (1979). Anim. Breed. Abstr., 48: 4966. Krogmeier, D. and Dzapo, V. (1991). Anim. Breed. Abstr., 60: 2449. Lukefahr, S.D. et al. (1983). J. Anim. Sci., 57: 1108-1116. Mc Nitt, J.I. and Lukefahr, S.D. 1990. J. Anim. Sci., 68: 1505-1512. Mc Nitt, J.I. and Moody, G.L. Jr. (1990). J. Appl. Rabbit Res., 13: 169-175. Poornima, K. et al. (2002). Indian J. Anim. Sci., 72: 601-603. Reddy, K.V.G. et al. (2003). Indian J. Anim. Sci. 73: 97-99. Reddy, S.S. et al. (2000). Indian Vet. J. 77: 597-599. Singh, G. (1996). World Rabbit Sci. 4: 79-83.