MUSCLE GROWTH AND DISTRIBUTION IN SWINE AS INFLUENCED BY LIVEWEIGHT, BREED, SEX AND RATION

Abstract

Muscle distribution was studied in 109 Duroc × Yorkshire, Hampshire × Yorkshire and Yorkshire × Yorkshire barrows and gilts fed either high or low energy rations (3652 and 2757 kcal DE/kg, containing 19.9% and 15.3% protein, respectively) and slaughtered at 23, 68, 91 or 114 kg liveweight. Individually dissected muscles from half carcasses were grouped into nine "standard muscle groups" and expressed as percentages of total side muscle. Slight changes occurred in muscle distribution between 23 and 68 kg liveweight, but remained quite constant thereafter. Breed groups were quite similar except that Duroc × Yorkshire pigs had a significantly greater percentage of muscle in the spinal group. The influence of sex appeared to vary relative to liveweight, with gilts maturing at earlier weights than barrows. Ration influence was negligible except for the distal thoracic limb group, which had a slightly greater percentage of muscle in pigs on the HE ration than the LE ration. Unexplained interactions between sex and ration and sex and breed effects occurred for the thorax to thoracic limb muscle group. Comparisons of the present pig data with those from cattle indicated that, in pigs, diphasic growth patterns may not be as pronounced as in cattle, and that individual muscles may be growing proportionate to total muscle very early in life. There seemed to be little evidence to indicate that selection pressures have had any influence on changing the muscle distribution in swine.