Investigation of the productivity and carcass composition of sheep with a muscle hypertrophy gene
A series of experiments were conducted to determine the mode of inheritance of the muscle hypertrophy condition; to characterize reproduction and wool production of females; to characterize growth rate, feed intake and feed efficiency of lambs with muscle hypertrophy; and to evaluate the effect of the muscle hypertrophy phenotype on carcass cutability, muscle mass and muscle distribution in sheep.
Two hundred thirty-six ewes were mated to heterozygous rams expressing muscle hypertrophy. Three hundred eleven lambs were weaned and classified by muscle phenotype. These data suggest that muscle hypertrophy in sheep is inherited through a dominant autosomal gene. The post-weaning growth rate of lambs with muscle hypertrophy did not differ (P < .2) from the growth rate of normal-muscled lambs. Feed efficiency was superior (P < .03) for lambs with muscle hypertrophy and feed intake was lower. Reproductive performance of ewes with muscle hypertrophy was comparable to the performance of normal-muscled ewes. Fleece weight and staple length were lower (P < .01) in ewes with muscle hypertrophy than in controls.
Eighteen paternal half-sibling ram lambs representing two muscle phenotypes were slaughtered at 54.5 kg to evaluate carcass composition and muscle weight distribution. Lambs with muscle hypertrophy had higher (P < .0005) dressing percentages and had a higher (P < .0001) percentage of their carcass weight in the muscles of the pelvic limb and torso than half-siblings. Lambs with muscle hypertrophy had a higher (P < .01) percentage yield of trimmed, boneless retail cuts than normal-muscled controls. Internal organ and testicle weights did not differ significantly between muscle phenotypes.
In summary, these data indicate that sheep with muscle hypertrophy are comparable to normal-muscled half-siblings in growth rate and reproductive performance and are superior in feed conversion and carcass composition. The potential economic impact of sheep with muscle hypertrophy on the commercial sheep industry should be significant.