Environmental variation and breed sensitivity for growth rate and backfat depth in pigs

This study investigated the magnitude of environmental variation and compared the environmental sensitivity of Large White, Landrace and Duroc pigs based on reaction norms analyses for lifetime average daily gain (ADG) and backfat depth (BF). Data comprised 265 165 records collected between 2000 and 2010 on pigs from nine herds in Australia. Four environmental descriptors [the phenotypic mean and three least-squares means of contemporary groups (CG) of linear mixed models fitting fixed effects only or fitting sire or animal as additional random effects] were compared in order to quantify the environmental variation based on herd-by-birth month (HBM) and herd-by-birth week (HBW) CG for ADG and BF. Similar levels of variation were found for environmental descriptors based on HBM or HBW CG definitions for both traits but the accuracy of estimates for environmental descriptors was higher for HBM than HBW. The standard deviations of environmental descriptors were 31 (35) g/day for ADG and 1.0 (1.1) mm for BF based on the animal model fitting HBM (HBW), which are similar to the genetic standard deviations usually observed for these traits. Most of this variation in environmental conditions was also observed within years and within herds. Landrace had the highest ADG and Large White had the lowest BF across the environmental range. Significant breed-by-environment interaction was found for ADG but not for BF. Duroc was least sensitive and Large White was most sensitive indicating that the leaner breed was less able to perform consistently across the observed range of environmental conditions in this study.