Genomic imprinting and environmental epigenetics: Their influence on sheep reproductive traits across parities

This study aimed to explore the impact of genomic imprinting on the genetic variance of composite reproductive traits across three parities in Baluchi sheep. The traits analyzed included litter mean weight per lamb born (LMWLB), litter mean weight per lamb weaned (LMWLW), total litter weight at birth (TLWB), and total litter weight at weaning (TLWW). We employed a univariate linear animal model for each trait, treating performance across parities as separate traits. Twenty-four animal models were assessed, incorporating direct additive genetic effects, maternal genetic effects, maternal permanent environmental effects, direct and maternal genetic covariances, as well as maternal and paternal imprinting. Model selection was based on Akaike's Information Criterion (AIC). Direct heritability estimates for the traits were generally low, ranging from 0.039 ± 0.017 for LMWLW to 0.085 ± 0.028 for TLWW. TLWB and TLWW exhibited higher heritability than LMWLB and LMWLW in their respective parities. In the best model (model 24), maternal imprinting heritability estimates from the first to third parity were 0.059 ± 0.016, 0.060 ± 0.013, and 0.085 ± 0.021 for TLWB, 0.075 ± 0.021, 0.068 ± 0.025, and 0.048 ± 0.016 for LMWLB, 0.051 ± 0.013, 0.065 ± 0.019, and 0.068 ± 0.020 for TLWW, and, 0.072 ± 0.012, 0.057 ± 0.018 and 0.054 ± 0.011 for LMWLW, respectively. Paternal imprinting heritability estimates were consistently lower than maternal imprinting estimates, with values across parities ranging from 0.001 ± 0.024 to 0.019 ± 0.032 for TLWB, 0.005 ± 0.022-0.010 ± 0.019 for LMWLB, 0.012 ± 0.05-0.017 ± 0.05 for TLWW and, 0.013 ± 0.01-0.016 ± 0.01 for LMWLW. In conclusion, imprinting effects should be included in breeding programs to increase the accuracy of genetic evaluation.