S.E. Williams

Biceps femoris and rump fat as additional ultrasound measurements for predicting retail product and trimmable fat in beef carcasses.

One hundred ninety-eight steers of Angus and Hereford breeding were evaluated 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. Carcass measurements associated with the USDA yield grade were also obtained. Carcasses were fabricated into closely trimmed (.32 cm fat), boneless subprimals. Regression procedures were used to predict weight and the percentages of retail product and trimmable fat. Final weight (FINALWT) accounted for most of the variation when predicting kilograms of retail product and trimmable fat, with R2 values of .836 and .435, respectively. As single predictors URUMP and UFAT accounted for most of the variation when predicting the percentages of retail product and trimmable fat with R2 values of .244 and .220, respectively. Adding URUMP to equations that included FINALWT, UREA, and UFAT increased R2 values for percentage of retail product from .175 to .318 and for weight of retail product from .847 to .865, whereas the addition of UROUND did not appreciably increase R2 values for the same models. Adding URUMP and UROUND to the model of FINALWT, UREA, and UFAT to predict kilograms and the percentage of trimmable fat increased R2 values from .530 to .610 and from .254 to .360, respectively. Models using live-animal measurements to predict weight and the percentage of retail product gave R2 values equal to models using the actual measurements found in the USDA Yield Grade equation.