Genetic parameters for growth, muscularity, feed efficiency and carcass traits of young beef bulls
Résumé
Genetic parameters were estimated for feed efficiency and live performance traits of 678 Blonde d'Aquitaine (BA) and 708 Limousin (LI) bulls born between 1991 and 2007, and for carcass traits of 3755 BA and 5263 LI progeny. Records at weaning were registered on-farm in 277 BA and 298 LI herds having provided purebred males for the French selection scheme of progeny tested bulls destined to artificial insemination. Analyzed traits included weight (WW) and muscle score (WM) recorded at weaning, and weight (LW) and muscle score (LM) recorded on bulls in performance test stations at 15 months. Feed intake (FI), residual feed intake (RFI) and feed conversion ratio (FCR) were also recorded in performance test stations. Carcass traits recorded in progeny test stations were age-adjusted carcass weight (CW), dressing percentage (DP), European commercial score for carcass muscularity (CM) and carcass internal fatness score (CF). Multivariate analyses were performed on different trait combinations using BLUP animal model and REML methodology. Heritability estimates for WW, WM, LW, LM, FI, RFI, FCR, CW, DP, CM and CF were 0.27, 0.31, 0.57, 0.64, 0.30, 0.26, 0.30, 0.53, 0.62, 0.47 and 0.47 for BA, respectively, and 0.35, 0.35, 0.63, 0.51, 0.48, 0.45, 0.23, 0.61, 0.47, 0.54 and 0.38 for LI, respectively. Genetic correlations (rg) between live performance traits and the corresponding carcass traits were strong in both breeds, ranging from 0.52 to 0.98. Thus, an early selection on live traits recorded at weaning should improve carcass value of young bulls. In both breeds, genetic correlations were null to weak between growth and muscularity at weaning and feed utilization traits (|rg| < 0.30). LW was strongly genetically correlated with FI (|rg| > 0.71) but weakly to moderately negatively with RFI and FCR (|rg| < 0.30). In both breeds, RFI was genetically independent from CF and weakly related to DP. Over the period 1991–2007, realized genetic trends estimated on males entering AI bull test stations were clearly positive on CW. For BA and LI bulls, annual trends were equal to 3.9% and 5.0% of genetic standard deviation (σg) per year, respectively. Estimated trends were lower for CM (1.3% and 3.7% σg per year, respectively), for RFI (− 1.5% and 0.0% σg per year, respectively) and FCR (− 1.0% and − 2.3% σg per year, respectively).