Genetic evaluation of mothering ability for multiple parities in Iberian pigs

The usefulness of genetic progress for litter size in pig breeding is limited by mothering ability and piglets survival. It is a critical aspect for breeds used as dam lines, in which litter weight (LW) at weaning could be an alternative selection goal. Our objective was to investigate the genetic basis of LW at 21days for the six first parities in 1,449 Iberian sows with available records from 2,709 litters without crossfostering. REML genetic parameters were estimated using an animal model with repeatability (RM), a multitrait animal model (MTM), and a random regression model (RRM). Estimated parameters for LW21d using the RM model were: heritability, h = 0.13 (SE = 0.02) and ratio of permanent environmental variance to total variance, p = 0.12 (SE = 0.02). Heterogeneity of h estimates across parities was observed using the MTM model, being the h values for the first six parities 0.31, 0.08, 0.16, 0.13, 0.01 and 0.31 (SE from 0.01 to 0.04). The genetic correlations between parities ranged from 0.58 to 0.99, but most of them were above 0.80. The variance ratios estimated using a RRM model were h = 0.26, 0.21, 0.19, 0.13, 0.09 and 0.19, and p = 0.08, 0.18, 0.20, 0.20, 0.17 and 0.09. The genetic correlations between the first parity and the later ones were lower than 0.70, and the genetic correlations between parities higher than 2 were greater than 0.90. A system of genetic evaluation of LW21d based on RRM models would be useful to improve the persistency of mothering ability in the later parities.