Jumping into selective sweeps for sport horse performance

P237 Jumping into selective sweeps for sport horse performance. In recent years, specialized breeding programs for sport horse performance have been developed to increase genetic gain and they have nowadays become common practice in elite studbooks. However, it is still not fully understood which regions of the genome such programs impact. This study aimed at identifying selective sweeps in the genome of 2 clusters of Swedish Warmblood horses (SWB) based on genetic relationships. These 2 clusters represent horses showing high breeding values either for dressage (DR) or show jumping (SJ) abilities. We analyzed high-density genotype data (670K) from 193 DR and 187 SJ horses belonging to these clusters. Haplotype selective sweeps were identified via XPEHH test by detecting those alleles that underwent directional selection in one population, while remaining polymorphic in the other one. Selection signatures were averaged over windows to minimize the number of false positives and to account for large standard variations. Only regions defined as a 500 kb-window showing an average XPEHH higher than 3.0 or lower than −3.0 (P < 0.001) were considered as putative signatures of selection. These regions were then compared with known QTL regions in the Horse QTL Database. In SJ horses, haplotype selective sweeps were detected on ECA7, ECA13, ECA21, ECA22, ECA26 and ECA31. On ECA22, the haplotype homozygosity exceeded the 500 kb window up until 2.5 Mb. In DR horses, ECA1, ECA4, ECA9, ECA25 and ECA28 showed potential selective sweeps, with 2 regions on ECA4 and 3 regions on ECA25. Three overlapping QTL regions in SJ horses associated with performance and health traits were found. In DR horses, haplotype selective sweep regions coincided with 2 QTLs related to sport performance abilities. The results from this study show that specialized breeding programs can lead to significant haplotype diversity within sub-populations belonging to the same breed.