The use of real-time ultrasound measurements to predict composition and estimate genetic parameters of carcass traits in live beef cattle

Abstract

Four hundred ninety-seven steers and 247 bulls were ultrasonically measured for subcutaneous fat thickness (UFAT) and longissimus muscle area (ULMA) between the 12th and 13th ribs just previous to slaughter over a three-year period to evaluate the accuracy of ultrasound measure­ ments. Carcass measurements from experienced evaluators were thon used as a basis from which to compare ultrasound. The cattle used were part of a serial scan and serial slaughter project and consequently a great deal of variation in carcass measurements was experienced. Overall, carcass means and (ranges) were as follows: carcass weight 342 kg (227483 kg); fat thickness (CFAT) 1.16 cm (.13-4.06 cm); and longissimus muscle area (CLMA) 79.9 cm^ (60.6-115.5 cm^). The mean differences between carcass and ultrasound measurements, indicative of average bias, 2 were .032 cm and -1.47 cm for FAT and LMA, respectively, indicating that FAT was slightly underestimated and LMA was overestimated. Further evaluation of these differences indicates that, in general, fatter animals (CFAT > 1.27) were underestimated and leaner animals (CFAT 90.3 cm were more likely to be underestimated by ultrasound while those with CLMA < 83.9 2 cm were more likely to be overestimated. Mean absolute values of the differences between carcass and ultrasound measurements gave an indica2 tion of the average error and were .227 cm and 5.09 cm for FAT and LMA, respectively. The thickness of CFAT had a significant (P < .05) effect on the error of UFAT measurements with leaner animals being more accu­