Evaluation of foetal growth, litter size and reproductive performance in rabbit after 18 generations of selection for growth rate using cryopreserved embryos

Abstract In livestock, adverse effects on reproductive performance, health traits and robustness have been demonstrated in animals selected for high production and efficiency. Using embryo cryopreservation and rederivation, we compared phenotypic traits between rabbit populations separated for 18 generations under growth rate selection pressure (R18 vs R36). To do so, embryos from the ancestral population (R18) and the most recent population (R36) were vitrified in 2000 and 2015, respectively, and rederived and grown together in a randomized controlled environment in 2015. To eliminate confounding maternal and embryo handling effects, traits were measured in the second generation after rederivation (R20 and R38 generations). Our study suggests that selection for growth rate has no adverse effect on litter size components. Thus, in the R38 generation we observed a significant increase in embryo implantation (7.2 ± 0.71 vs 5.1 ± 0.79) and litter size (7.1 ± 0.29 vs 6.5 ± 0.32). Besides, the foetal sac area at day 12 of gestation (2.44 ± 0.070 vs 2.07±0.071 mm2, for R38 vs R20, respectively), and foetal placenta area (136.7 ± 6.14 vs 116.0 ± 6.31 mm2, for R38 vs R20, respectively) and crown-rump length of the foetus (38.0 ± 0.68 vs 35.8 ± 0.68 mm, for R38 vs R20, respectively) at day 19 of gestation were higher in the R38 generation. Altogether, these results show that selection for growth rate does not adversely affect components of litter size, foetal growth and reproductive performance. However, the extent to which foundation criteria play a role in the high prenatal and perinatal mortality rate remains unclear in paternal lines.