Two Single Nucleotide Polymorphisms in the Myostatin (GDF8) Gene Have Significant Association with Muscle Depth of Commercial Charollais Sheep

To assess whether the same mutation(s) were responsible for similar phenotypes attributed to ovine chromosome 2 (OAR2) quantitative trait loci (QTL) in different sheep breeds, Suffolk, Texel and Charollais rams from British commercial flocks were genotyped for two single nucleotide polymorphisms (SNPs) located in the myostatin (GDF8) region of OAR2, previously detected in progeny of Belgian Texel rams exhibiting muscular hypertrophy. The first SNP (g.-2449G>C) was located upstream from the transcription start site and the second SNP (g.+6723G>A) in the 3' UTR of GDF8. The g.-2449C and g.+6723A alleles were absent in the Suffolk sires sampled, almost fixed in the Texel and segregating in the Charollais sires. Mixed model association analyses using SNP data on 338 Charollais lambs from 17 paternal half-sib families and phenotype and pedigree data on 56 500 lambs revealed that both SNPs had a significant association with muscle depth (P < 0.001). The SNPs were segregating at intermediate frequencies (p = 0.3) and exhibited strong linkage disequilibrium (r(2) = 0.90). Animals with the g.+6723AA genotype had significantly greater muscle depth than those with either the g.+6723GG or the g.+6723AG genotypes (P < 0.002), with the g.+6723A allele, the likely causative mutation, having an additive effect of 1.20 (+/-0.30) mm and a dominance effect of -0.73 (+/-0.36) mm. Based on estimated allelic effects and sample allele frequencies, the g.+6723G>A SNP explained 14% of the additive genetic variance of muscle depth. The maximum genetic variance for the trait (38%) attributed to the SNP would be attained at a g.+6723A allele frequency of 0.7. Our findings indicate that marker-assisted selection using these two GDF8 SNPs would be beneficial for the Charollais breed.