A genome-wide association study for racing performances in Thoroughbreds clarifies a candidate region near the MSTN gene

Using 1400 microsatellites, a genome-wide association study (GWAS) was performed to identify genomic regions associated with lifetime earnings and performance ranks, as determined by the Japan Racing Association (JRA). The minimum heritability (h(2) ) was estimated at 7-8% based on the quantitative trait model, suggesting that the racing performance is heritable. Following GWAS with microsatellites, fine mapping led to identification of three SNPs on ECA18, namely, g.65809482T>C (P=1.05E-18), g.65868604G>T (P=6.47E-17), and g.66539967A>G (P=3.35E-14) associated with these performance measures. The haplotype of these SNPs, together with a recently published nearby SNP, g.66493737C>T (P=9.06E-16) in strong linkage disequilibrium, also showed a very clear association with the performance (P<1E-05). The candidate genomic region contained eight genes annotated by ENSEMBL, including the myostatin gene (MSTN). These findings suggest the presence of a gene affecting the racing performance in Thoroughbred racehorses in this region on ECA18.