Genetics of slaughter precocity and its relations with carcase traits in double-muscled Piemontese young bulls and heifers

Double-muscled cattle breeds show limited adipogenesis, making “fatty” phenotypes difficult to record and direct selection for fatness unfeasible. In the Piemontese population, age at slaughter, carcase weight and gain were analysed in 11,058 young bulls and 6,334 heifers (Dataset 1) using a multiple-trait REML model. Age at slaughter showed moderate heritability (0.19 in males, 0.26 in females), similar to carcase weight (0.18 and 0.21). However, strong negative genetic correlations were observed between age at slaughter and carcase weight (-0.83 in males, −0.47 in females), indicating that genetically faster-growing animals are slaughtered earlier. An experimental survey on 1,161 young bulls (Dataset 2) included carcase fatness scores, which revealed a significant negative genetic correlation with age at slaughter (−0.62) through a Bayesian threshold-linear sire model. This suggests that animals genetically predisposed to higher fat deposition tend to be slaughtered earlier. Thus, age at slaughter may serve as a proxy for slaughter precocity in terms of both carcase gain and fatness. Performance testing of 5,333 male calves (Dataset 3) confirmed strong genetic correlations between live weight/daily gain and carcase weight/daily gain (0.55–0.86), and negative correlations with age at slaughter (−0.79 to −0.85). These results indicate that performance testing of AI candidate calves is a valuable tool not only to improve growth rates in young bulls and heifers, but also to enhance slaughter precocity. Further research should clarify the relationships between slaughter age, carcase fatness, meat quality and cow reproductive efficiency, particularly through molecular genetic approaches.