THE GROWTH AND DISTRIBUTION OF MUSCLE IN BULLS AND HEIFERS OF TWO BREEDS

Abstract

A trial is reported comparing muscle growth and distribution in 12 bulls and 12 heifers of each of two breed-types: Hereford (HE) and Dairy Synthetic (DY). Serial slaughter was carried out from weaning (163 ± 15.1 days) to approximately 15 mo of age. After slaughter, the left side of each carcass was broken into quarters and then eight wholesale cuts, which were separated into fat, muscle and bone. The growth pattern of muscle in each cut relative to total side muscle was estimated from the growth coefficient, b, in the allometric equation (Y = aXb). Growth coefficients were homogeneous among breeds and sexes, indicating that neither breed nor sex influenced relative muscle growth. Some significant (P < 0.05), though minor, sex and breed differences were found when muscle weight distribution was adjusted to constant side muscle weight. Notably DY heifers had significantly (P < 0.05) more muscle in the high-priced cuts (sum of round, sirloin, loin and rib) than either HE heifers or bulls of either breed-type. When muscle weight was adjusted to constant side weight, bulls were found to have a greater weight of muscle in the high-priced cuts than heifers, and DY animals to have more than HE animals.