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) rangin g in age from approximately 8 to 20 mo in a production setting in west ern Nebraska were used to estimate genetic (co)variances. Further info rmation used in the analyses, including weaning weight (WWT), postwean ing ADG, and scrotal circumference (SC), was obtained from the America n Angus Association, St. Joseph, MO, for these individuals and for ani mals from the same herd and contemporary groups. Data were analyzed us ing single-trait, sire model, restricted maximum likelihood (REML) pro cedures to estimate starting variances for later two-trait analyses. T hese two-trait analyses were done to estimate variance components for WWT coupled with BFT, LMA, SC, and ADG, also using REML procedures, bu t with a sire-maternal grandsire model for WWT and a sire model for th e other trait(s). Heritabilities for BFT, LMA, WWT direct, WWT materna l, SC, and ADG were .56, .11, .19, .24, .56, and .51, respectively. Ge netic 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 t o 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.