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

Abstract

Early-weaned Simmental steers (n = 192) were individually fed over 4yr (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 calculated 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 5yr 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.