Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 17, 1998
Publication Date: N/A
Interpretive Summary: A gene with large effects on lean and fat development of sheep was investigated. The name of the gene is callipyge and sheep with specific forms of the gene have extreme values for important traits. Callipyge and normal lambs have similar growth rates, but the dressing percentage of callipyge lambs is 55.9% compared 51.7% for normal lambs. Callipyge lambs have more rapid growth of lean tissue and less rapid growth of fat tissue relative to normal lambs. Consequently, callipyge carcasses have 24.3% fat and 71.3% lean, whereas normal carcasses have 31.5% fat and 64.0% lean. Callipyge lambs can be grown to heavier weights while still producing lean carcasses. Crossbreeding systems to exploit the callipyge gene could be used by the sheep industry to lower the cost of producing lean lamb.
Technical Abstract: A resource flock of 362 F2 lambs provided phenotypic and genotypic data to estimate effects of callipyge (CLPG) genotypes on growth, slaughter, and carcass traits. A contrast of CLPG genotypic effects, based on the paternal polar overdominance model, was used to evaluate callipyge and normal phenotypes. Callipyge and normal lambs did not differ for growth traits measured from birth to slaughter. Callipyge lambs produced 55.9% o live weight as chilled carcass weight compared to 51.7% for normal lambs at the same mean live weight of 48.32 kg. Lighter pelt, kidney-pelvic fat, and liver weights contributed to this advantage of callipyge lambs for dressing percentage (P < .001). Estimated accretion rates of carcass protein at the mean slaughter age were 12.5 and 10.2 g/d for callipyge and normal carcasses, respectively. Corresponding values for carcass fat were 35.2 and 42.1 g/d. Compositional differences in favor of callipyge carcasses were detected at constant values of slaughter age, carcass weight, and 12th rib fat depth. Callipyge carcasses had 2.56 kg greater fat-free lean and 1.39 kg less fat than normal carcasses at the same mean age of 214.9 d (P < .001). Callipyge carcasses consisted of 24.3% fat and 71.3% fat-free lean compared to 31.5 and 64.0% for normal carcasses at 25.6 kg of carcass weight. When evaluated at .49 cm of 12th rib fat depth, callipyge lambs were 15.4 d older and produced 4.1 kg heavier carcasses with 4.3% less fat (P < .001). Effects of CLPG genotypic groups on carcass composition were greater than virtually all reported breed substitution effects. Use of the CLPG mutant allele in structured mating systems can dramatically increase production of lean lamb.