Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/8/1995
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 for this effect. Compared to normal lambs, these lambs have superior feed efficiency and carcass composition. Since lambs begin to show the muscling characteristics sometime after birth, dystocia is not a problem in carrier sheep and, thus, provides the sheep industry with a number of advantageous traits. The mechanisms through which this condition manifests itself are not known. We conducted these experiments to: 1) further characterize the effects of this gene on muscle growth and meat quality and 2) determine the mechanism through which these effects are brought about. Our results indicate the presence of this gene increased muscle weight by 27.6% and decreased all measures of carcass fatness. The data indicate that this massive increase in muscle weight is caused by increasing muscle protein synthesis and decreasing the rate at which muscle proteins are broken down. The major problem with this gene is its negative effect on meat tenderness. Thus, to be of acceptable palatability, callipyge meat must be tenderized prior to consumption, otherwise meat toughness could preclude the use of this genetics in the sheep industry.
Technical Abstract: The present experiment was conducted to determine the effect of the callipyge gene on traits affecting muscle growth and meat tenderness. Dorset wethers (n = 40) which were either carriers or non-carriers of the callipyge gene were grain fed and slaughtered at 169 d of age. Genotype did not affect slaughter weight, hot carcass weight, or weights of the heart, spleen, viscera, kidney-pelvic fat, head, and pelt; however, callipyge lambs had a higher dressing percentage and lighter lungs, liver, and kidneys. Callipyge lambs had reduced fat thickness and marbling score and increased leg scores and longissimus area (34%). Adductor (30%), biceps femoris (42%), gluteus group (31%), longissimus (32%), psoas group (20%), quadriceps femoris (18%), semimembranosus (38%), and semitendinosus (26%) weights were increased in the callipyge phenotype; however, genotype did not affect weights of infraspinatus or supraspinatus. Longissimus myofibril fragmentation index was reduced at 1 (27%), 7 (35%), and 21 (37%) d postmortem and Warner-Bratzler shear force was increased at 1, 7, and 21 d postmortem in the callipyge phenotype. Shear force values of callipyge lambs at 21 d postmortem tended to be greater than shear force values of non-carriers at 1 d postmortem. Activities of calpastatin (83%) and m-calpain (45%) were increased by callipyge; however, u-calpain activity was not affected. Longissimus and semitendinosus RNA concentration, DNA content, RNA content, protein content, and the RNA:DNA ratio were increased in the callipyge phenotype. These results suggest that both reduced rate of protein degradation and increased capacity for protein synthesis are consequences of callipyge gene.