GROWTH AND DISTRIBUTION OF MUSCLE IN DOUBLE MUSCLED AND NORMAL CATTLE

Abstract

Eighteen Double Muscled (DM), 18 Beef Synthetic (SY) and 18 Hereford (HE) bulls, serially slaughtered from approximately 250 to 800 kg liveweight, were used to determine the influence of maturity type and "double muscling" upon muscle growth patterns and distribution. The left side of each carcass was dissected into major carcass tissues and the weights of individual muscles were obtained and grouped into nine standard anatomical groups. Relative to total side msucle (TSM), breed types tended to have similar growth coefficients for all muscle groups except muscles surrounding the spinal column where HE tended to have a higher growth coefficient than either DM or SY. As TSM increased, the proportion of muscle found in proximal hindlimb, distal hindlimb and distal forelimb decreased (b < 1; P < 0.05), the proportion of muscle in abdominal wall and proximal forelimb remained relatively constant (b = 1; P > 0.05) and the proportion of muscle in thorax to forelimb, neck to forelimb and intrinsic muscles of neck and thorax increased (b > 1; P < 0.05). At the same TSM, compared with the other breed types, DM tended to have more of their muscle in the hip and stifle region but less in the distal parts of both limbs and in neck and thorax. The hyperdevelopment of the large superficial muscles of the proximal part (thigh) and the hypodevelopment of the distal part in the hindlimb give the DM animal the typical 'bottle thigh' appearance. Key words: Bulls (young), muscle growth, muscle distribution, Double Muscled, cattle