One hundred seventy-three steer calves, selected at weaning to represent USDA classifications for frame size (Large, L; Medium, M; Small, S) and muscle thickness (No. 1, No. 2, No. 3), were assigned to three finishing diets (grain, 3.03 Mcal ME/kg DM; silage, 2.46 Mcal ME/kg DM; forage, 2.06 Mcal ME/kg DM), forming a 3 x 3 x 3 factorial with unequal subclass numbers. The steers were slaughtered at constant weights corresponding to their respective frame size classifications (L = 590 kg, M = 499 kg; S = 408 kg). Individual live weights were recorded every 28 d during finishing and, following slaughter, one side of each carcass was dissected into muscle, bone and fat. Diet interacted with frame size to affect growth rate. Frame-related differences in growth rate were very pronounced among grain-fed steers (L greater than M greater than S) but became smaller in magnitude as feeding intensity was reduced. Diet also had a significant effect on percentage separable carcass fat, despite the fact that the steers were slaughtered at a similar percentage (approximately 60%) of their estimated potential mature weights. Carcasses produced by grain-finished steers were fattest, and those produced by forage-finished cattle were leanest. The comparative fatness of steers finished on silage was dependent on frame size. Within the L class, carcasses produced by silage-finished steers were comparatively lean and were similar in fatness to carcasses produced by forage-finished cattle. Conversely, S steers finished on silage produced carcasses that were comparable in fatness to carcasses from grain-finished cattle. Frame-related differences in percentage carcass fat were significant only within the silage treatment group (S greater than L). Differences in carcass muscle-to-bone ratio were directionally consistent with visually discernible differences in feeder cattle muscling (No. 1 greater than No. 2 greater than No. 3). The effects of muscle thickness on muscle-to-bone ratio were most pronounced within the L class.(ABSTRACT TRUNCATED AT 400 WORDS)
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.