Genetic correlation estimates between ultrasound measurements on yearling bulls and carcass measurements on finished steers

Carcass and growth measurements of finished crossbred steers (n = 843) and yearling ultrasound and growth measurements of purebred bulls (n = 5,654) o f 11 breeds were analyzed to estimate genetic parameters. Multiple-trait re stricted maximum likelihood (REML) was used to estimate heritabilities and genetic correlations between finished steer carcass measurements and yearli ng bull ultrasound measurements. Separate analyses were conducted to examin e the effect of adjustment to three different end points: age, backfat thic kness, and weight at measurement. Age-constant heritability estimates from finished steer measurements of hot carcass weight, carcass longissimus musc le area, carcass marbling score, carcass backfat, and average daily feedlot gain were 0.47, 0.45, 0.35, 0.41, and 0.30, respectively. Age-constant her itability estimates from yearling bull measurements of ultra-sound longissi mus muscle area, ultrasound percentage of intramuscular fat, ultrasound bac kfat, and average daily postweaning gain were 0.48, 0.23, 0.52, and 0.46, r espectively. Similar estimates were found for backfat and weight-constant t raits. Age-constant genetic correlation estimates between steer carcass lon gissimus muscle area and bull ultrasound longissimus muscle area, steer car cass backfat and bull ultrasound backfat, steer carcass marbling and bull u ltrasound intramuscular fat, and steer average daily gain and bull average daily gain were 0.66, 0.88, 0.80, and 0.72, respectively. The strong, posit ive genetic correlation estimates between bull ultrasound measurements and corresponding steer carcass measurements suggest that genetic improvement f or steer carcass traits can be achieved by using yearling bull ultrasound m easurements as selection criteria.