Evaluation of sire by environment interactions for growth rate and backfat depth using reaction norm models in pigs.

Reaction norm models for sires were used to evaluate genotype by environment interactions for lifetime average daily gain (ADG) and backfat depth (BF) in pigs recorded at 143 days. Data for ADG and BF were available for 265 103 pigs recorded in Australia between 2000 and 2010 in nine herds. The full data set and two subsets based on minimum numbers of progeny per sire of 50 and 100 were analysed. The environmental descriptor was quantified as least square means of herd-by-birth month (HBM) contemporary groups which varied from 540 to 738 g/day for ADG and from 8.2 to 13.8 mm for BF. Several models were evaluated for estimation of variance components in terms of predictive ability for sire intercepts and slopes. The accuracy of genetic parameter estimates was improved by increasing family size, fitting models with a fixed regression coefficient on the environmental descriptor instead of fixed HBM effects and heterogeneous residual variances. Significant sire by environment interactions were found for ADG but not for BF. Heritability estimates for ADG ranged from approximately 0.21 in average environments to approximately 0.30 in the most unfavourable environments. Estimates of sire intercepts and slopes varied by 98.5 g/day and 0.253 g/day per g/day for ADG, respectively. Lowly negative correlations between sire intercept and slope do not support the hypothesis that high growth is associated with larger environmental sensitivity.