Polygenic Prediction of Equestrian Sport Discipline Among Horses Bred for Jumping and Dressage.

Horses bred for different equestrian sports vary in physical, physiological and behavioural requirements. Characterising genetic markers associated with discipline provides an opportunity to improve identification of horses best suited to either jumping or dressage. Using a composite selection signals test, genomic regions under positive selection in German warmblood horses divergent for discipline were identified that contained lead SNPs proximal to or within genes with functions relevant to the requirements for jumping and dressage. Dressage genes function in tortuosity of movement (GRM5) and responsiveness to touch (PROKR2), and have roles in bone development (VWC2, THSD7B, CYP27A1) and growth traits (VPS13B, TMEFF2, NANOS1, ZEB2). Jumping genes function in the modulation of neuropathic pain (LPAR6 and SLITRK1) and encode compounds commonly included in nutritional supplements (CHST15 and TPH2). A polygenic prediction score (PPS) derived from 28 SNPs had an AUC = 0.89, and categorical predictions for dressage and jumping had an overall accuracy of 80%. Among horses with jumping competition records, the jumping genetic profile was highest among elite performers (85.7%) and lowest among inferior performers (69.4%). The PPS could be applied to efficiently and accurately identify young horses most suitable for each discipline before they reach the age for participation in physical performance assessments, and the genetic markers could be applied in genome-enabled breeding strategies to accelerate genetic gain in sport horses. Furthermore, examination of the PPS among Thoroughbred horses indicated that it could be used to inform suitable second careers for racehorses to improve welfare outcomes following retirement from racing.