Food intake, growth and body composition in Australian Merino sheep selected for high and low weaning weight. 2. Chemical and dissectible body composition

Abstract

ABSTRACTThe changes in chemical and dissectible body composition from birth to maturity were examined in rams and ewes from flocks of Merino sheep selected for high (weight-plus) and low (weight-minus) weaning weight and from a randomly bred control flock. Body composition was examined in 34 mature animals and the maturing patterns for body components calculated using mean values from the mature animals and individual data from 106 immature animals.In the 34 mature animals, strain had no effect on the proportions of chemical and dissected fat, protein and muscle in the body. The weight-plus had greater proportions of ash and carcass bone in the body than the weight-minus animals. Mature rams had lower proportions of chemical and dissected fat and greater proportions of protein, muscle, ash and carcass bone in the body than mature ewes.The weight-minus animals had later maturing patterns for both chemical and dissected fat than the weight-plus animals. Strain had no effect on the maturing patterns for protein and muscle, although both ash and carcass bone were later maturing in the weight-plus, than in the weight-minus animals. Chemical and dissected fat were later maturing in the ewes than in the rams, whereas protein, muscle, ash and carcass bone were earlier maturing in the ewes than in the rams.The weight-minus animals were fatter at the heavier body weights, although there was a trend for the weight-plus animals to be slightly fatter at the lighter body weights. When compared at the same stage of maturity of body weight, strain differences in the proportion of fat in the body declined as the animals matured. Compositional differences between the rams and ewes varied according to the body weight or stage of maturity of body weight at which they were compared.