Podium:Identifying Genomic Regions Undergoing Selection in Racehorses

Intense breeding for speed over a relatively small number of generations has resulted in elite athletic performance within Thoroughbred, Quarter Horse and Standardbred racehorses. The goals of this study were to: 1) identify the genomic regions undergoing selection in these three breeds; 2) investigate haplotype sharing among racehorse breeds; and 3) identify putative candidate genes that contribute to the racing phenotype.

Five hundred and forty-six Standardbreds, 519 Thoroughbreds, and 24 Quarter Horses were genotyped at, or imputed up to, 2 million SNP markers distributed across the genome. Genomic regions harboring signatures of selection were identified using two F_ST-based statistics (di and hapFLK), and local haplotype sharing among individuals of each breed was calculated using the hapQTL software. Genomic regions of interest (ROIs) were defined as those in which significant di windows (99^th percentile of the empirical distribution) and hapFLK values (-log10[p-value] > 3) overlapped with significant SNP markers found by hapQTL (-log10 [Bayes factor] > 5). Seventy-five ROIs, distributed across 22 autosomes and the X chromosome, averaging between 10kb and 1.5Mb in length, were prioritized for further investigation. Ninety-two equine transcripts were identified within ROIs, retrieved using the BioMart software, and investigated for their association with racing ability. Pathway analysis was performed to identify protein-coding genes significantly associated with main metabolic pathways that might contribute to the racing phenotype. 

Next, WGS data from these three breeds will be used for the discovery and annotation of biologically relevant allelic variants that might account for their increased racing ability.