Predicting Carcass Composition in Early-Weaned Simmental Steers Using a Combination of Real-time Ultrasound, Live Evaluation, Carcass Expected Progeny Differences, and GeneSTAR Marbling Marker

Early-weaned Simmental steers (n = 192) were individually fed over 4 yr (48 head/ yr) to determine if real-time ultrasound (RTU), live evaluation, carcass expected progeny differences, GeneSTAR marbling, or a combination could accurately predict marbling composition. Steers were fed a high-concentrate diet for 249.7 ± 0.7 d and harvested at 423.3 ± 1.4 d of age. The RTU scans were recorded for ribeye area, intramuscular fat (IMF), and back fat thickness at 60-d intervals with final ultrasound scans taken ≤ 13 d prior to harvest. Yearling BW, marbling (MARB), percentage of retail cuts, and carcass weight expected progeny differences were calcu-lated for each steer. Visual estimations of quality and yield grade were made ≤ 7 d prior to pre-harvest by 3 evaluators. Average price data over 5 yr were used for dressed beef, grid premiums, and discounts. GeneSTAR did not affect (P > 0.10) IMF deposition. Genetic, live, and carcass parameters were regressed on chemical IMF, dressed price, and profit using stepwise regression analysis. For chemically determined IMF, 67.0% of the variation was explained by RTU quality grade (R² = 0.585), percentage of retail cuts (R² = 0.030), and MARB (R² = 0.028), indicating that RTU was the only major contributor. Approximately 17% of the variation in average dressed price was explained by RTU. GeneSTAR MARB marker was not an accurate indicator of intramuscular deposition of early-weaned Simmental steers; however, MARB expected progeny difference (EPD) was correlated to IMF deposition. Live evaluation better estimated yield grade than quality grade. Real-time ultrasound most accurately predicted MARB, carcass value, and profit.