Bone distribution patterns in sheep selected for high and low weaning weight

Abstract

AbstractThe change in the proportional distribution of bone weight within the carcass skeleton from birth to maturity was examined in rams and ewes from flocks of Australian Merino sheep selected for high (weight plus) and low (weight minus) weaning weight and from a randomly selected control flock. Data from 140 animals (106 immature, 34 mature) were used. Shape parameters for the long bones of the limbs in the 34 mature animals were derived by determining the allometric relationship between bone length, diameter and individual bone weight.Selection for increased and decreased weaning weight resulted in a concomitant increase and decrease in mature size and total bone weight. In the weight plus group, total bone as a proportion of body weight also increased but selection had little effect on the proportional distribution of bone weight within the skeleton at any stage of maturity. This was the product of similar growth patterns within the skeletal system aiming towards a similar mature distribution pattern for each strain.Within the strains of different mature size there was a difference between mature rams and ewes in both total bone weight as a proportion of body weight and in the proportional distribution of this bone weight. This was associated with differences in the maturing patterns of the bones of the hindlimb and the pelvic girdle.Neither selection nor sex affected the relationship between bone shape and bone weight, although the difference in bone weight between the strains and sexes at maturity meant that they also differed in bone shape at this point.