Similar to humans, the VO2max in horses is usually limited by oxygen supply to the mitochondria rather than by mitochondrial oxidative capacity,CT99021 with the respiratory system in horses unable to meet the metabolic demands of exercising muscle. Although the physical and physiological adaptations contribut-ing to elite athleticism in Thoroughbred are well described, the genes contributing to an athletic phenotype have not yet been identified. Domestic animal species provide valuable opportunities to identify genes underlying phenotypes that have been strongly selected because discrete breeds have arisen relatively recently from a small number of founder animals. The Thoroughbred population is a closed population established in the 16th and 17th centuries from crosses between local Galloway and Irish hobby horses with imported Eastern stock. As with many domesticates, the Thoroughbred originates from a small number of founders; just one founder stallion contributes to 95% of paternal lineages and ten founder mares account for 72% of maternal lineages. However, despite a limited number of founders and strong selection for racetrack performance some 35% of variation in performance is heritable. These population demographics coupled with intense recent selection for athleticism offer a unique opportunity to identify genomic contributions to exercise-related traits. A number of approaches may be taken to identify genes underlying phenotypic adaptations. Whereas a candidate gene approach requires a priori knowledge of gene function and linkage mapping requires information about familial relationships as well as access to samples from large numbers of relatives, Silmitasertib hitchhiking mapping using population genetics-based approaches evaluates the effects of natural or artificial selection across whole genomes in populations of unrelated individuals that have been subjected to differential selection pressures for the trait or traits of interest. Although it is generally considered that microsat-ellites themselves will not be subject to selection, loci closely linked to the microsatellites will influence their population genetic behaviour. Therefore we have employed a hitchhiking mapping approach to identify signatures of positive selection in the Thoroughbred genome and to localise genomic regions containing genes influencing exercise-related phenotypes.