The objective of this study was to evaluate correlations between ultrasonography measurements and carcass traits of 115 steers (Nellore, ½ Angus-Nellore, ½ Simmental-Nellore, and Canchim) averaging 329 kg of initial body weight and two different finishing frame sizes (small and large). After 120 days in a feedlot, body weight, rib eye area (RA), and fat thickness (FT) were measured by ultrasound. Following slaughter, carcass RA and FT measurements and weights of hindquarter, forequarter, and commercial cuts were all taken; body composition was also determined. Yields of carcass, retail cuts, and hindquarter as well as ratios of ultrasound RA per 100 kg of body weight and ultrasound RA per 100 kg of carcass weight were calculated. Data showed higher muscle deposition in ½ Simental-Nellore and Canchim and greater fat deposition in Nellore while ½ Angus-Nellore steers combined both characteristics. According to the results, RA was a good indicator of the proportion of muscle present in the carcass and selection for increasing carcass RA may decrease FT because of the negative correlation between FT and hindquarter percentage and RA. Frame size did not affect carcass composition possibly due to the small variation between both groups. Because correlations of measured and ultrasound RA and FT with carcass components yielded similar results, it was possible to validate ultrasound measurements to predict carcass composition of young bulls.
carcass yield; composition; fat; muscle; retail cuts
