Genetic parameter estimates of live animal ultrasonic measures of retail yield indicators in yearling breeding cattle

Ultrasonic measures of backfat thickness (BFT) and longissimus muscle area (LMA) taken on Angus bulls (n = 805) and heifers (n = 877) ranging in age from approximately 8 to 20 mo in a production setting in western Nebraska were used to estimate genetic (co)variances. Further information used in the analyses, including weaning weight (WWT), postweaning ADG, and scrotal circumference (SC), was obtained from the American Angus Association, St. Joseph, MO, for these individuals and for animals from the same herd and contemporary groups. Data were analyzed using single-trait, sire model, restricted maximum likelihood (REML) procedures to estimate starting variances for later two-trait analyses. These two-trait analyses were done to estimate variance components for WWT coupled with BFT, LMA, SC, and ADG, also using REML procedures, but with a sire-maternal grandsire model for WWT and a sire model for the other trait(s). Heritabilities for BFT, LMA, WWT direct, WWT maternal, SC, and ADG were .56, .11, .19, .24, .56, and .51, respectively. Genetic correlations between WWT direct and WWT maternal, WWT direct and LMA, WWT maternal and LMA, WWT maternal and BFT were -.57, .42, .01, and -.69, respectively. Genetic parameters from this study were used to calculate possible genetic change with a typical selection scenario, and it was shown that among WWT, BFT, and LMA, BFT could be affected the most by selection, relative to its mean.