Food intake, growth and body composition in Australian Merino sheep selected for high and low weaning weight 6. Muscle-weight distribution

Abstract

ABSTRACTThe change in muscle-weight distribution from birth to maturity was examined in rams and ewes from strains of Australian Merino sheep which had been selected for high or low weaning weight, and from a randomly bred control flock. The proportional distribution of total muscle weight among nine anatomically standardized muscle groups was determined for 34 mature animals. The growth of each group was then assessed relative to the growth of the total musculature, using data from 106 immature animals. Maturity coefficients were calculated separately for pre- and post-weaning growth. Several muscle groups exhibited a diphasic growth pattern.Selection for high and low weaning weight resulted in an increase and decrease respectively in total muscle weight in mature animals, but had no effect on mature muscle-weight distribution. There were no significant strain effects on maturing patterns of muscle groups, except during the pre-weaning growth of muscles around the spinal column and those connecting the thorax to the forelimb. When compared at the same stage of maturity there was little difference between the strains in muscle-weight distribution. However, at the same weight the larger mature-size strain had a more immature pattern of muscle-weight distribution.The total muscle weight of mature rams was greater than that of mature ewes. Sex also had an effect on muscle-weight distribution at maturity for seven of the nine muscle groups. At maturity rams had a higher proportion of their muscle weight in those muscle groups associated with the neck and thorax, and a lower proportion in those associated with the limbs. Sex affected the pre-weaning maturing pattern of the muscles of the spinal column, and the post-weaning maturing pattern of all muscle groups, with the exception of those muscles associated with the distal hindlimb, the spinal column, and those attaching the thorax to the forelimb.