Australian Sheep Breeding Values for Worm Egg Count Retain Predictive Power Across Flocks in the Presence of GxE

Abstract

Genotype by environment interactions (GxE) for worm egg count (WEC) in Merino sheep were estimated in eight environments across Australia from the Sheep CRC Information Nucleus flock (IN). Genetic correlations between environments were estimated using a factor analytic model, with mean correlations for each environment ranging from 0.27 to 0.57 for an overall mean of 0.40, confirming the presence of large GxE effects for WEC. The industry genetic evaluation model for WEC fits a direct genetic effect averaged across environments, which is reported back to breeders as the Australian Sheep Breeding Value (ASBV), with a sire by environment interaction term to accommodate deviations in performance (not reported to breeders). This model was validated using the IN data, with results demonstrating that the average genetic effect does retain predictive power across environments, albeit with lower accuracy due to a lower heritability observed in the sire interaction model when GxE effects are large.