Genetic parameter estimates for finished steer carcass and yearling bull ultrasound measurements
Carcass and growth measurements of finished crossbred steers (n = 843) of multiple breeds and yearling ultrasound and growth measurements of purebred bulls (n = 5654) of 11 breeds were an analyzed to estimate genetic parameters. Multiple trait restricted maximum likelihood (REML) was used to estimate heritabilities and genetic correlations between steer hot carcass weight (SHCW), steer carcass ribeye area (SREA), steer carcass backfat (SBFAT), steer carcass marbling score (SMAR), steer average daily feedlot gain (SADG), bull ultrasound ribeye area (BREA), bull ultrasound backfat (BBFAT), bull ultrasound percent intramuscular fat (BIMF), and bull average daily post weaning gain (BADG). Three end-points were considered: backfat, age and weight at measurement. Backfat constant genetic correlations between SREA and BREA, SMAR and BIMF, and SADG and BADG were .57, .68, and .87, respectively. Age constant genetic correlations between SREA and BREA, SBFAT and BBFAT, SMAR and BIMF, and SADG and BADG were .66, .80, .88 and .72, respectively. Weight constant genetic correlations between SREA and BREA, SBFAT and BBFAT, SMAR and BIMF, and SADG and BADG were .82, .75, .90 and .46, respectively. The strong, positive genetic correlation estimates between steer carcass measurements and corresponding bull ultrasound measurements suggest that genetic improvement for steer carcass traits can be achieved by using yearling bull ultrasound measurements as selection criteria.