Association of cytochrome c oxidase COX2 haplotypes with the matrilineal structure and performance of Thoroughbred horses

The study of the mitochondrial genome of Thoroughbred is of significant interest both for assessing the differentiation of the matrilineal structure of the breed and for finding genes that determine the performance of horses. Objective: the aim of the presented work to study the variability of COX2 haplotypes in female lines of the Thoroughbred breed and their association with the racing performance of horses. Materials and methods: genotyping of 40 Thoroughbred mares by mtDNA haplogroups and cytochrome c oxidase COX2A>G types was carried out by the Sanger method in the genetics laboratory of the All-Russian Research Institute of Horse Breeding. When identifying nucleotide sequences, data from GenBank were used on 17 nomenclature haplogroups placed under access numbers: JN398377-JN398457 and EF597513- EF597514. The results of sequencing the control region of the D-loop of mtDNA were analyzed in the Mega 12 program. When analyzing the COX2 sequence, the author's primers and the GenSeq reagent kit were used. The racing performance of horses was evaluated based on a set of indicators, including the total amount of winnings, the average winnings per race, the success rate, the distance of victories, and the best speed. Results . Three variants of cytochrome c-oxidase COX2 were identified in the tested horses, with the presence of haplotype A in all female lines. Haplotype G was only observed in mares of L haplogroup. Thoroughbred mares with haplotype A had a more successful racing career compared to those with the A/G variant (P >0.05). Conclusions. The variability of COX2A>G gene haplotypes in Thoroughbred horses is associated predominantly with the L mtDNA haplogroup, which complements the information about the matrilineal structure of the breed and the mitochondrial genome.