An evaluation of the use of ultrasound scanning to predict carcass traits in steers grain fed for the Japanese market

Abstract

The value of live-animal ultrasound scanning was assessed for steers grain-fed according to Japanese market specifications. Ultrasound scanning of the live animal for rump fat depth at the P8 site and for longissimus muscle area at feedlot entry did not accurately predict the ranking of individual steers on subcutaneous fat depth andlongissimus muscle area measured on the carcass at slaughter. When scanning was performed at the time of feedlot exit, up to 9 months later, the prediction of post-slaughter subcutaneous fat depth using scanned measurements made at the P8 site was of higher precision. Ultrasonic scanning to determine longissimus muscle area on feedlot exit was no better as a predictor of carcass longissimus muscle area than was that scanned at feedlot entry. The low correlations were probably due to differences in the sites of the scan (12th/13th rib interface) and longissimus muscle-area measurement (10th/11th rib interface) and to measurement errors in both the ultrasonic scan and the direct carcass measurements. Ultrasonic scan measurements may have been afiected by interference from deep fat cover on the steers. Genetic correlations were high but imprecisely estimated. Correlations between live-animal scanned measurements and the corresponding carcass measurements were high for steers from the same vendor property. Heritability estimates for the scanned measurements were in agreement with those from other studies.