Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/17/1995
Publication Date: N/A
Interpretive Summary: In 1983, a farmer from Oklahoma noticed that offspring of a ram in his flock had excessive muscling. Since then, it has been demonstrated that a single gene is responsible. The gene has been called callipyge. Our previous experiments indicated that this gene had a major effect on carcass composition by decreasing fatness and increasing muscle mass. Total muscle weight was increased by 27.6%. The objective of the present experiment was to determine if carcass composition of lambs carrying the callipyge gene could be further enhanced by sex-condition (ram vs wether) and by administration of growth-promoting compounds. Results indicate neither of these treatments were able to further enhance muscle growth and carcass composition of callipyge lambs. In agreement with our previous data, meat from these lambs was excessively tough and, thus, in order for industry to fully benefit from this germplasm, meat tenderization technologies must be utilized.
Technical Abstract: The objective of this study was to determine the effects of dietary administration of a beta-adrenergic agonist (BAA; L-644,969) and male sex-condition (ram vs wether) on muscle growth and meat quality of Dorset X Romonov lambs believed to be heterozygous for the callipyge gene. At about 17 wk of age, lambs were blocked by weight within each sex- condition and randomly assigned to BAA treatment group. The interaction of BAA and male sex-condition was not significant for any of the traits measured. Rams had greater initial and final live weights, average daily gain, and hot carcass weight (P < .01). Rams did not differ (P > .05) from wethers with respect to any of the carcass traits, possibly because the wethers were so lean and heavily-muscled that there was little room for improvement. Kidney-pelvic fat weight was reduced 26% by BAA (P < .05). Knife separable lean weight and whole carcass proximate composition were not affected (P > .05) by BAA or male sex-condition. BAA increased calpastatin activity at 20 d (1.1 vs 1.5 units/g), but not at 0 h (3.9 vs 4.8 units/g) postmortem, decreased myofibril fragmentation index (60.7 vs 44.9), and increased shear force (8.2 vs 10.9 kg) at 20 d postmortem (P < .05). These data suggest that muscle growth rates are near maximum in lambs expressing the callipyge gene, regardless of male sex-condition or BAA treatment. Therefore, it appears that the callipyge gene exerts most, but not all, of its effect through similar intracellular events as BAA.