An evaluation of grading parameters and fabrication yields of beef carcasses.

Two experiments were performed to evaluate grading parameters and fabrication yields of beef carcasses. In Exp.1, single-sired beef steers (n=56) were blocked (n=28 per block) by implant status and sorted into pairs by weight. Each pair was then randomly assigned to a harvest day (0, 28, or 56) and dietary intake level [maintenance (M) or ad libitum (AL)] that was applied within d 28 and 56. Additionally, supplementation of zilpaterol hydrochloride (ZH) was randomly applied within a pair for each of M and AL diet levels. Steers that were randomly assigned to a treatment were fed ZH continuously at 90 mg for 20 d following a withdrawal period of 4 d before harvest. Steers (BW= 603.5 ± 48.1 kg) were harvested at a commercial processing facility, allowed a 24 h chill period, and then left carcass sides were transported to the West Texas A&M University Meat Laboratory for fabrication. Each side was fabricated into subprimals to determine individual red meat yield (RMY), trimmable fat yield (TFY), and bone yield (BY). Results indicated that RMY tended (P < 0.07) to differ by harvest day (0= 64.0, 28= 63.3, 56= 62.5 %), intake (M= 63.4, AL= 62.1 %), and treatment (C= 61.4, ZH= 63.7 %). Comparatively, TFY was impacted (P < 0.04) by harvest day (0= 20.9, 28= 21.0, 56= 22.4 %), intake (M= 20.5, AL= 23.3 %), and treatment (C= 23.5, ZH= 21.3 %). In Exp.2, the ability of the United States Department of Agriculture (USDA), Canadian Beef Grading Agency (CBGA), and Japanese Meat Grading Association (JMGA) grading systems as well as bioelectrical impendence technology (BIA) to accurately predict red meat yield and trimmable fat yield were evaluated using fabrication results from Exp 1. Pearson correlations were generated between the actual RMY% and each grading system and BIA. Resulting correlations indicate that the equation for boneless closely trimmed retail cuts from the round, loin, rib and chuck from the USDA grading system demonstrated the highest correlation (r = 0.71) followed by the Canadian yield equation (r = 0.61), and lastly the Japanese estimated yield equation (r = 0.36). Moreover, the equation developed from this study using BIA measurements, accounted for 72% of the variation in RMY%, respectively. These results indicate that the USDA grading system provides the best prediction of RMY and BIA technology can be used as an accurate, noninvasive predictor of beef carcass composition.