COMPARISON OF LIVE AND CARCASS EQUATIONS PREDICTING PERCENTAGE OF CUTABILITY, RETAIL PRODUCT WEIGHT, AND TRIMMABLE FAT IN BEEF-CATTLE

Forty-four Hereford-sired steers were measured ultrasonically for back fat and longissimus muscle area between the 12th and 13th ribs before slaughter and visually appraised for fatness, overall muscling, and fr ame. Carcass measurements associated with USDA yield and quality grade s were measured and recorded. Carcasses were fabricated into closely t rimmed, boneless subprimals at 1.27- and .32-cm fat trim levels. Cutab ility percentage (percentage of retail cuts from the cold carcass weig ht) and kilograms of retail product were defined three ways. The first definition included only retail cuts from the round, loin, rib, and c huck. The second included the above plus adjusted lean trim from the r ound, loin, rib, and chuck, and, finally, total retail product from th e entire carcass. Kilograms (TOTFAT) and percentage (PERFAT) of trimma ble fat were also calculated. Stepwise regression procedures were used for live and carcass trait model development predicting cutability pe rcentages, kilograms of retail product, and trimmable fat. Fat measure ments accounted for the largest portion of variation in cutability per centage and PERFAT. Weight measurements accounted for the major source s of variation in predicting kilograms of retail product arid TOTFAT. Final models using live animal traits ranked the steers equally as wel l for cutability percentages as the original USDA cutability equation and stepwise, developed carcass equations(P > .10). Final models using live animal or carcass equations ranked the animals equally for kilog rams of retail product yield (P > .10).