Estimation of correlated response on growth traits to selection in litter size of rabbits using a cryopreserved control population and genetic trends

An experiment is performed to contemporaneously compare young rabbits six generations apart in order to evaluate the correlated response to selection on growth traits in a line selected on litter size at weaning for 21 generations. The selection method was based on a BLUP procedure using a repeatability animal model. The contemporary comparison was possible because techniques of embryo cryopreservation and transfer were used in generation 15. The direct response to selection between both generations has been studied by Garcia and Baselga [Livest. Prod. Sci. 44 (2002) 45–53] and was 0.51±0.25 rabbits weaned/litter (0.085 per generation). In this paper, growth traits have been studied and the results show that non-significant differences between both generations were found, using as covariate total litter size at birth. Also, heritability, genetic correlations between growth traits and litter size at weaning, and genetic trends have been estimated using mixed model methodology with all the data of the selection process (12 651 parities and 93 085 growth records across 21 generations of selection). The genetic correlations were close to zero and the estimated genetic trend for weaning weight and post-weaning daily gain were positive and significant but small, less than 0.3% of the means per generation.