Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: March 1, 1998
Publication Date: N/A
Technical Abstract: The objective is to discuss industry breeding structures and mating systems that manage callipyge alleles to produce relevant distributions of genotypes. Based on the polar overdominance model of gene action, the mutant callipyge allele (C) and the normal wild type allele (N) interact to cause expression of callipyge (CN genotype with C allele from the sire and N allele from the dam) and normal (CC, NC, and NN genotypes) phenotypes. Subjective evaluation of sheep distinguishes between callipyge and normal phenotypes, allowing reliable detection of CN sheep. The C allele can be introgressed by mating CC, CN, or NC rams of any breed to NN ewes of the intended breed. Resulting callipyge (CN) crossbred rams are mated to NN ewes of the intended breed and the process is repeated. The C allele may eventually be fixed by mating CN rams and ewes and using available methods to identify CC progeny. In time, CC rams could be mated to CN ewes, relying on subjective evaluation to assign callipyge (CN) ewes to the carrier flock and normal (CC) sheep to the homozygous flock. Terminal sire mating systems are ideally suited to produce CN progeny expressing the callipyge phenotype. Rams of specialized terminal sire lines homozygous for the C allele are mated to noncarrier purebred, F1, or composite ewes, producing callipyge market lambs. Heterozygous rams are also useful under certain situations; for example, CN or NC rams mated to NN ewes produce callipyge market lambs and noncarrier lambs available as replacement stock. Effective industry exploitation of callipyge alleles requires use of well- managed purebred and crossbred mating systems. Perhaps the callipyge phenomenon will encourage and stimulate the industry to evaluate its breeding structure, resulting in more prudent use of genetic resources.