Genotype by trait-specific season interactions for farrowing rate and average piglet birthweight

The aim of this study was to investigate if there are interactions between genotype and traitspecific seasons (GxTrS) for average piglet birth weight and farrowing rate from sow litters. A series of bivariate animal models were used to estimate genetic parameters. The current study found GxTrS for farrowing rate (genetic correlation <0.4), but not for average piglet birth weight (genetic correlation >0.9). Farrowing rate recorded in the least stressful season (low temperature and positive change in day length) was genetically different to farrowing rate recorded in the two most stressful seasons (high temperature and increasing day length or high temperature and decreasing day length). The results of this study showed that seasonal infertility in sows can genetically be improved by using trait-specific seasons. However, the heritability of farrowing rate was very low (h² =0.02) and improving the temperature control in the sow’s housing environment and developing effective strategies to minimise the effects of changes in day length on the sows may be more effective to improve seasonal infertility.