Genotype by environment interaction for milk yield in Sarda dairy sheep

Abstract

Genotype by environment interaction (GEI) for milk yield (ME) wasinvestigated by analyzing 40 140 first lactation records performed in 538 flocks. Flock–year effects from national genetic evaluation were used to define low (L), medium (M) and high (H) yielding environments. Differences observed between adjacent subsets were approximately 20% of the trait overall mean. Sire variance components estimated using multitrait analysis were 58, 82 and 149% of the estimate from the complete dataset (L, M and H, respectively) and genetic correlation coefficient between extreme subsets was 0.66, lower than genetic correlations obtained from randomly sampled subsets. Rank correlation coefficients between estimated transmitting abilities (ETA), obtained independently within L, M and H subsets for 71 AI rams having at least 10 daughters per subset, were lower than one (ranging from 0.42 to 0.56). These results strongly supported the existence of GEI for milk yield in Sarda sheep flocks. The influence of GEI on phenotypic responses in flocks differing in yield level could be due to a reduced expression of genes under conditions of restricted environmental opportunity. Splitting the selection scheme according to farming conditions does not seem a suitable solution for the Sarda breeding program. Thus, to provide farmers with genotypes suitable to exhibit a good phenotypic expression in different conditions, the selection across all environments, in which the descendants are expected to perform, still seems the best option.