Estimation of genetic and phenotypic parameters for ultrasound and carcass merit traits in crossbred beef cattle

Ultrasound measurements of 852 crossbred steers along with carcass merit measurements on 756 of them were used to examine their genetic and phenotypic parameters. Traits including ultrasound backfat thickness (UBF), ultrasound ribeye area (UREA), ultrasound marbling (UMAR), carcass weight (CWT), carcass grade fat (CGF), carcass average backfat thickness (CABF), carcass ribeye area (CREA), carcass marbling score (CMAR), and carcass lean meat yield (CLMY) were measured on 6 yr of residual feed intake trials from 2003 to 2008. Pairwise bivariate animal models were performed for each combination of traits using ASReml software to estimate heritability, phenotypic and genetic correlations among the traits. Significant fixed effects (contemporary group, and sire breed), covariates (age of dam, slaughter weight, and start test age of animal), and random additive effect were fitted in the models. The heritability estimates for UBF, UREA, UMAR, CWT, CGF, CABF, CREA, CMAR, and CLMY were 0.31, 0.17, 0.37, 0.40, 0.22, 0.25, 0.24, 0.38, and 0.28, respectively. Most of the phenotypic correlations were significant (P < 0.05). CWT had low to moderate phenotypic correlations with most of the traits. Results show that heavier CWT tends to have more UREA, CGF, CABF, and CREA. Genetic correlations among these traits varied from weak to strong, but most of them were not significantly different from zero. Greater CREA may lead to decreased UMAR, and UBF due to negative genetic correlations (-0.56+/-0.32, and -0.45+/-0.23, respectively). The results support the potential value of ultrasound technology in crossbreed beef cattle breeding programs to generate indicator traits for carcass quality. In addition, carcass lean meat yield correlated favourably with backfat thickness and rib eye area but correlated unfavourably with UMAR. The estimated genetic parameters for ultrasound and carcass merit traits can be incorporated into breeding programs that emphasize carcass quality in Canadian crossbred beef cattle populations.