Phenotypic characterization of rambouillet sheep expressing the callipyge gene: I. Inheritance of the condition and production characteristics.

Abstract

The objectives of this study were to determine the model of inheritance of the callipyge gene and to evaluate the growth, ADFI, feed efficiency, reproductive performance, and wool growth of sheep that are heterozygous for the callipyge gene. Ewes (n = 236) with a normal muscle phenotype and genotype were mated to three heterozygous rams that expressed the callipyge gene. Lambs (n = 311) were subjectively classified at weaning (90 to 120d) according to muscle phenotype by a panel of three evaluators working independently. The callipyge muscle phenotype was expressed in 150 lambs, whereas 161 lambs expressed a normal muscle phenotype. The percentage of lambs expressing the callipyge muscle phenotype (48.2%) did not differ (P > .1) from the expected 50%. Growth rate was similar for lambs of both phenotypes regardless of sex. Feed efficiency was superior (P < .05) for both male and female lambs with the callipyge muscle phenotype. Average daily feed intake was lower for male (P < .02) and female (P < .004) lambs with the callipyge muscle phenotype. Grease fleece weight and staple length at 12 mo were superior (P < .03) for ewes with a normal muscle phenotype. These results indicate that the callipyge gene in sheep is dominant when inherited from the paternal parent and lambs expressing the callipyge gene have increased feed efficiency and reduced ADFL.

Evaluation of the ovine callipyge locus: II. Genotypic effects on growth, slaughter, and carcass traits.

“…These results are consistent with those of Jackson et al (1997a), who report that no differences were detected between callipyge phenotypes for birth weight, weaning weight, and postweaning daily gain. However, compositional targets for callipyge sheep can be achieved at greater live and carcass weights.…”

“…Accordingly, the lighter weight of internal organs is consistent with the reduced daily feed intake of callipyge compared with normal lambs (Jackson et al, 1997a). Jackson et al (1997a) reported that callipyge phenotype decreased 12-mo fleece weights of yearling Rambouillet ewes by approximately 18%. These researchers hypothesized that dietary amino acids were preferentially converted to lean tissue growth rather than to wool growth.…”

“…A positive correlation of weights of metabolically active internal organs with daily feed intake of sheep has been established (see review of Koong et al, 1985). Accordingly, the lighter weight of internal organs is consistent with the reduced daily feed intake of callipyge compared with normal lambs (Jackson et al, 1997a). Jackson et al (1997a) reported that callipyge phenotype decreased 12-mo fleece weights of yearling Rambouillet ewes by approximately 18%.…”

The callipyge mutation and other genes that affect muscle hypertrophy in sheep

“…These superior carcass traits translate into improved yields of wholesale leg, loin, rack, and shoulder from callipyge animals by 11.8%, 4.7%, 2.5%, and 2.3%, respectively, over normally muscled lambs [9]. In addition, callipyge lambs exhibit superior feed efficiencies and lower daily feed intakes [24], which result in lower production expenses. Therefore, the widespread production of callipyge lamb would have the potential to lower the cost of lamb for consumers and to increase the profitability of the sheep industry.…”

“…In an extensive survey of 19 muscles dissected from the right side of carcasses from normal and callipyge individuals [26], the total weight of excised muscles from the pelvic, torso, and thoracic limbs was greater in callipyge lambs by 42%, 50%, and 14%, respectively, than in normally muscled half-sibs. This muscle hypertrophy develops after about three weeks of age [24], so there is no increased risk of dystocia for callipyge lambs.…”