BICEPS FEMORIS AND RUMP FAT AS ADDITIONAL ULTRASOUND MEASUREMENTS FORPREDICTING RETAIL PRODUCT AND TRIMMABLE FAT IN BEEF CARCASSES

One hundred ninety-eight steers of Angus and Hereford breeding were ev aluated ultrasonically for fat thickness over the 12-13th rib (UFAT), fat thickness over the rump (URUMP), 12-13th longissimus muscle area ( UREA), and depth of the biceps femoris (UROUND) before slaughter. Carc ass measurements associated with the USDA yield grade were also obtain ed. Carcasses were fabricated into closely trimmed (.32 cm fat), bonel ess subprimals. Regression procedures were used to predict weight and the percentages of retail product and trimmable fat. Final weight (FIN ALWT) accounted for most of the variation when predicting kilograms of retail product and trimmable fat, with R(2) values of .836 and .435, respectively. As single predictors URUMP and UFAT accounted for most o f the variation when predicting the percentages of retail product and trimmable fat with R(2) values of .244 and .220, respectively. Adding URUMP to equations that included FINALWT, UREA, and UFAT increased R(2 ) values for percentage of retail product from .175 to .318 and for we ight of retail product from .847 to .865, whereas the addition of UROU ND did not appreciably increase R(2) values for the same models. Addin g URUMP and UROUND to the model of FINALWT, UREA, and UFAT to predict kilograms and the percentage of trimmable fat increased R(2) values fr om .530 to .610 and from .254 to .360, respectively. Models using live -animal measurements to predict weight and the percentage of retail pr oduct gave R(2) values equal to models using the actual measurements f ound in the USDA Yield Grade equation.