MSTN genotype (g.66493737C/T) association with speed indices in Thoroughbred racehorses

Sequence variation at the equine myostatin gene (MSTN) locus has previously been shown to have a singular genomic influence on optimum race distance in Thoroughbred racehorses. Myostatin, encoded by the MSTN gene, is a member of the TGF-β superfamily that regulates skeletal muscle development in a range of mammalian species including the horse. In the Thoroughbred, the C-allele at the g.66493737C/T SNP has been found at significantly higher frequency in subgroups of the population that are suited to fast, short distance, sprint races and also influences body composition phenotypes. We investigated the influence of the g.66493737C/T SNP on speed indexes measured in a cohort of n = 85 Thoroughbred horses-in-training. We found significant associations between genotypes at the g.66493737C/T SNP and all measured speed variables: Dist(6) [distance travelled during 6 s before and after maximal velocity (V(max)); P = 0.0040], V(maxt) (duration at V(max); P = 0.0249), V(max) (P = 0.0265), Dist(6b) (distance travelled during 6 s before V(max); P = 0.0032), and Dist(6a)(distance travelled during 6 s after V(max); P = 0.0317). For each measure, horses with the C/C and C/T genotypes outperformed T/T horses, indicating the requirement for at least one C-allele to improve speed. For the most significantly associated variables (Dist(6) and Dist(6b)) the C/C cohort performed better than the T/T cohort with the heterozygotes intermediate, indicating a dose-dependent manifestation. These findings clearly indicate that variation at the MSTN gene influences speed in Thoroughbred horses.