Genetic Influences on Growth Patterns of Muscle and Bone in Young Bulls

Carcass composition and growth patterns for muscle and bone were compared among three breed-types (Hereford crossbred, (HC), beef synthetic (SY) and dairy crossbred (DC)). Sixteen bulls of each breed-type were weaned at about 6 mo and fed a high concentrate ration ad libitum. The bulls were grouped four to a pen and randomly allocated to one of two slaughter weights (500 kg and 600 kg). Breed-types differed (SY vs. HC and DC) in the allometric growth coefficients of hot carcass weight regressed on liveweight indicating that the growth of the hot carcass relative to liveweight in SY bulls was higher than the interbreed average. No significant breed-type differences were found in the regression of sample muscle and bone on various size dimensions. Breed-types differed significantly in amount of bone adjusted to common sample muscle, carcass and liveweight. Since breed-type allometric regressions were in all cases homogeneous, the difference in composition reflected differences already apparent at the first slaughter point (500 kg).