AN EVALUATION OF THE USE OF ULTRASOUND SCANNING TO PREDICT CARCASS TRAITS IN STEERS GRAIN FED FOR THE JAPANESE MARKET

The value of live-animal ultrasound scanning was assessed for steers g rain-fed according to Japanese market specifications. Ultrasound scann ing of the live animal for rump fat depth at the P8 site and for longi ssimus muscle area at feedlot entry did not accurately predict the ran king of individual steers on subcutaneous fat depth and longissimus mu scle area measured on the carcass at slaughter. When scanning was perf ormed at the time of feedlot exit, up to 9 months later, the predictio n of post-slaughter subcutaneous fat depth using scanned measurements made at the P8 site was of higher precision. Ultrasonic scanning to de termine longissimus muscle area on feedlot exit was no better as a pre dictor of carcass longissimus muscle area than was that scanned at fee dlot entry. The low correlations were probably due to differences in t he sites of the scan (12th/13th rib interface) and longissimus muscle- area measurement (10th/11th rib interface) and to measurement errors i n both the ultrasonic scan and the direct carcass measurements. Ultras onic scan measurements may have been affected by interference from dee p fat cover on the steers. Genetic correlations were high but imprecis ely estimated. Correlations between live-animal scanned measurements a nd the corresponding carcass measurements were high for steers from th e same vendor property. Heritability estimates for the scanned measure ments were in agreement with those from other studies.