28 Optimal Definition of Contemporary Groups for Crossbred Pigs in a Joint Purebred and Crossbred Genetic Evaluation

Abstract

Abstract In the pig industry, purebred animals are raised in nucleus herds and selected to produce crossbred progeny for commercial environments. Crossbred and purebred performances are different, correlated traits. All purebreds in a pen are assessed together at the end of a performance test. However, only selected crossbreds are removed (based on visual inspection) and measured at different times, creating many small contemporary groups (CG). This may reduce EBV prediction accuracies. Considering this sequential recording of crossbreds, the objective was to investigate the impact of different CG definitions on genetic parameters and EBV prediction accuracy for crossbred traits. Growth rate (GP) and ultrasound backfat (BFP) records were available for purebreds. Lifetime growth (GX) and backfat (BFX) were recorded on crossbreds. Different CG were tested: CG_all included farm, sex, birth year and birth week, CG_week added slaughter week, and CG_day used slaughter day instead of week. Data of 124,709 crossbreds were used. The purebred phenotypes (62,274 animals) included 3 generations of purebred ancestors of these crossbreds and their CG mates. Variance components for 4-trait models with different CG definitions were estimated with AIREML. Purebred traits’ variance components remained stable across CG definitions and varied slightly for BFX. Additive genetic variances (and heritabilities) for GX fluctuated more: 812±36 (0.28±0.01), 257±15 (0.17±0.01) and 204±13 (0.15±0.01) for CG_all, CG_week, and CG_day, respectively. The predictive ability, linear regression (LR) accuracy, bias, and dispersion of crossbred traits in crossbreds favored CG_day, but correlations with unadjusted phenotypes favored CG_all. In purebreds, CG_all showed the best LR accuracy, while showing small relative differences in bias and dispersion. Different GC scenarios showed no relevant impact on BFX EBV. This study shows that different CG definitions may affect evaluation stability and ranking. Results suggest that ignoring slaughter dates in CG is more appropriate for estimating crossbred trait EBV for purebred animals.