Phenotypic characterization of rambouillet sheep expression the callipyge gene: III. Muscle weights and muscle weight distribution.

Paternal half-sibling Rambouillet ram lambs (n = 18) representing two muscle phenotypes were slaughtered at 54.5 kg to evaluate the effect of the callipyge gene on muscle mass. Lambs were produced from a sire that was heterozygous for the callipyge gene. Nineteen muscles were dissected from the right side of each carcass to evaluate muscle weights relative to carcass weight. Excised muscle mass as significantly higher (42%) for lambs exhibiting a callipyge muscle phenotype than for half-siblings. In the pelvic limb, all excised muscles except the peronius tertius were larger in lambs expressing the callipyge gene (P < .001). In the torso, the longissimus (P < .001), psoas major (P < .001), and psoas minor (P < .01) were larger in lambs with the callipyge phenotype. In the thoracic limb, the biceps brachii (P < .001) triceps brachii (P < .002), and extensor carpi radialis (P < .01) were larger in lambs with the callipyge phenotype. Total pelvic limb (P < .001) torso (P < .001), and thoracic muscle weights were higher (P < .01) in lambs with the callipyge phenotype. Callipyge lambs had a higher (P < .01) percentage of excised muscle weight in the pelvic limb and torso and a lower (P < .01) percentage in the thoracic limb when compared to controls. These data indicate that the magnitude of expression of the callipyge gene is dependent upon the location of the muscle on the body and that the increased muscle mass was concentrated in the leg and loin.