Document Type : Original Article
Authors
1
Animal Production Research Institute, Agriculture Research Center, Ministry of Agriculture, Dokki, Cairo, Egypt.
2
Department of Animal Production, Faculty of Agriculture, Banha University, Moshtohor, Egypt.
Abstract
This study was carried out to estimate the genetic parameters for post-weaning body weight at 4, 6, 8, 10 and 12 weeks and growth rate during the periods 4-6, 6-8, 8-10 and 10-12 weeks in New Zealand White (NZW) rabbits. Data consisted of records of 3891 progenies born from 219 does and 65 sires during five consecutive years. The statistical analysis was carried out by weighted data using a single trait animal model to estimate additive, common litter effects and residual variances. The model included the fixed effects (season, parity and litter size at birth) and random effects (additive genetic and common litter effect in addition to random error) for post-weaning growth traits.
Estimates of CV% of body weights decreased with the advancement of age. CV% estimates for growth rate during periods were not consistent and slightly high. Estimates ofheritability for body weights ranged between low and moderate, from 0.13 to 0.20 at 4, 6, 8, 10 and 12 weeks of age, respectively. Estimates ofheritability were low and not consistent growth rate during the name periods and ranged from 0.06 to 0.13. Common litter effect (c2) of body weight at weaning was higher (0.69) compared to that at later age. It declined gradually with the advancement of age (0.54, 0.44, 0.37 and 0.32 at 6, 8, 10 and 12 weeks of age). Common litter effects (c2) of growth rate between weaning weight and 6 weeks were higher than all the other periods. Estimates of error proportions e2 for body weight ranged from 0.18 to 0.48, and were moderate or slightly high for growth rate during all periods. Estimates of minimum and maximum, all progeny, breeding values (BV) for body weight ranged from -0.244 to 0.389, from -0.245 to 0.362, from -0.259 to 0.346, from -0.195 to 0.235 and from -0.233 to 0.265 grams at 4, 6, 8, 10 and 12 weeks of age, respectively.
Breeding values decreased with advancement of age (0.633, 0.607, 0.605, 0.403 and 0.498 grams) at 4, 6, 8, 10 and 12 weeks of age, respectively. Also, their accuracies were high. Minimum, maximum and range of predicted breeding values ofgrowth rate were high during 4 to 6 weeks the period and decreased at 6 to 8, 8 to 10 and 10 to 12 weeks and their accuracies were high for all periods. Pearson and rank correlation were estimated among breeding values by STDFREML, all possible Pearson and rank correlation between body weight at different ages were low or moderate or high, positive and significant (0.03, 0.16 and 0.28), while the correlation were negative, low and not significant between body weight, at 4 and 6 weeks, between 6 and 8 weeks and between 10 and 12 weeks (-0.10, -.0.001and -0.004). Estimates of Pearson and rank correlation, between most growth rate during all the periods varied widely, low, moderate or high positive and significant (0.05, 0.14 and 0.34), while the correlation were negative, low and non significant during the period from 4 to 6 weeks (-0.004).
Conclusively, the estimates of heritabilities were moderate for body weight; selection at these ages may be a useful method for improving rabbit growth. The common litter effect is very important for post-weaning growth traits; one can conclude that the common litter effect should be included in the genetic evaluation of breeding programs. The correlation estimates are obviously age dependent and reveal that correlated response of selection is quite feasible.
Keywords
)
View on SCiNiTO