Genetic and phenotypic trends for carcass traits in Irish beef cattle

Animals subjected to intensive genetic selection require continuous monitoring to observe changes in economically important traits. The focus of this research was to estimate genetic and phenotypic trends for carcass traits for three genotypes: dairy dam and dairy sire (DxD), dairy dam and beef sire (DxB) and beef dam and beef sire (BxB). Linear regression models were used to generate genetic and phenotypic trends for carcass weight, conformation and fat score for both cows and prime animals (i.e. never parented an animal). Phenotypic trends for age at slaughter were also estimated in prime animals. Results indicated that carcass weight increased genetically by 1.1 kg per year for BxB animals, but decreased by 0.14 and 0.39 kg per year for DxB and DxD animals, respectively. Phenotypic trends reflected the genetic trends for carcass weight for DxB and BxB animals, but the decline in genetic trends for carcass weight for DxD animals was not replicated in their phenotypic trends. Carcass conformation declined genetically by 0.02 and 0.05 units per year for DxD and DxB animals, respectively, and increased by 0.05 units per year for BxB animals. Phenotypic trends for conformation were similar to genetic trends. Carcass fat showed a decrease genetically for DxD and BxB, but remained constant for DxB animals, although this was not reflected in the phenotypic trends. Age at slaughter decreased phenotypically for all genotypes. Current breeding programmes have a favourable impact on carcass traits for BxB animals, but an unfavourable trend was observed for DxD and DxB animals.