Selection for increased muscling improved feed efficiency and carcass characteristics of Angus steers

This project studied the effect of selection for divergence in live muscle score (MS) in a herd of Angus cattle on feedlot performance, feed efficiency, carcass characteristics and carcass yield of two cohorts of steer progeny. Steers from lines selected for low muscling (Low, n = 91, average MS = D-) and high muscling without (High, n = 76, average MS = C+) and with (High(Het), n = 61, average MS = B) one copy of the 821 del11 myostatin mutation were studied. Steers entered the feedlot for grain finishing at 16-18 months of age. Individual feed intake was measured during finishing, after which the steers were slaughtered to obtain commercial carcass and yield data. Low, High and High(Het) steers had similar weights at feedlot entry (442, 434, 441 kg, P = 0.11) and grew at similar rates during feed intake testing (1.42, 1.38, 1.37 kg/day, P = 0.3), but net feed intake declined with increasing muscling (0.34, -0.06, -0.40 kg DM/day, P < 0.001). Dressing percentage (54.2%, 54.9%, 56.5%, P < 0.001), retail meat yield (67.5%, 68.4%, 71.4%, P < 0.001) and retail meat : bone ratio (3.40, 3.55, 3.83, P < 0.001) progressively increased from Low to High to High(Het) steers. There were no significant differences for carcass rump and rib fat, or carcass fat yield between Low and High steers, but Low steers had higher marbling (P < 0.001). High(Het) steers had the least fat across all carcass fat measurements, including marbling (all P < 0.008). These results demonstrate that muscling was increased by selection for visual MS in British-breed cattle and resulted in greater meat yield via greater muscle to bone ratios.