Backfat as an Environmental Descriptor in Defining Growth Rate of the Pig: A GxE Analysis

Investigations of genotype by environment (GxE) interactions may use estimates of average performance observed for contemporary groups (CGs) as environmental descriptors (ED). Data from a commercial breeding herd of Large White pigs were used to define ED based on backfat (BF) and average daily gain (ADG). The ED of BF and ADG were estimated using an animal model, with sex, month-year CG, weight (BF only), litter size and parity of birth litter as fixed effects. Estimates of CG were centred, and then used to allocate an environment for each individual in the genetic analyses of ADG. Each ED was partitioned into quartiles, allowing ADG to be defined as a separate trait in the four environments based on BF or ADG. Heritability estimates for ADG ranged from 0.12 to 0.16 for BF as ED, and 0.07 to 0.17 for ADG as ED. There was a weak relationship between the BF ED and ADG ED indicating they do not quantify the environment in the same way. Nevertheless, the use of either ED indicates re-ranking of animals in different environments, with Pearson's correlations between EBVs ranging from 0.22 to 0.55 for BF as ED, and 0.43 to 0.54 for ADG as ED.