THE INFLUENCE OF BREED ON THE EFFICIENCY OF GROWTH AND MUSCLE DEPOSITION IN BULLS AND HEIFERS

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Abstract
Hereford (HE) and Dairy Synthetic (DY) breeds of both sexes were compared for various measures of efficiency in beef production. DY animals had greater (P < 0.001) birthweights and greater weaning weights (P < 0.001) than HE animals. At weaning, 16 animals of each breed-sex combination were grouped 4 to a pen and fed a high-concentrate cereal diet ad lib to 1 of 2 slaughter weights (485 kg, 575 kg). Average daily gain and liveweight gained per 100 MJ dietary energy (DE) was greater (P < 0.05) for DY bulls than HE bulls. Average daily gain, but not liveweight gained per 100 MJ DE, was greater (P < 0.05) for DY heifers than HE heifers. There were no differences (P < 0.05) in muscle gain per unit of liveweight among breed-sex combinations. At a constant liveweight DY bulls produced significantly (P < 0.05) more muscle than HE bulls and DY heifers significantly more (P < 0.05) than HE heifers. Muscle gain per 100 MJ DE was highest for DY bulls and lowest for DY heifers. For a constant amount of feed energy (23,241 MJ DE) DY bulls produced 20.1 kg (16%) more muscle than HE heifers. Breed and sex seem to cause important differences in the amount of carcass muscle produced for a constant energy intake.