Genome Diversity and the Origin of the Arabian Horse

The Arabian horse, one of the world's oldest breeds, is characterized by natural beauty, graceful movement, athletic endurance, and, as a result of its development in the arid Middle East, the ability to thrive in a hot, dry environment. Here we studied 449 Arabian horses from 12 countries using whole-genome re-sequencing and equine Single Nucleotide Polymorphism (SNP) arrays to examine hypotheses about genomic diversity, population structure, and the relationship of the Arabian to other horse breeds. We discovered an unexpectedly high degree of genetic variation and complex ancestry in Arabian horses from the Middle East region. Also surprisingly, and contrary to popular belief, we could detect no significant genomic contribution of the Arabian breed to the Thoroughbred. Genetic signatures in Arabians suggestive of selective sweeps contain candidate genes for combating oxidative damage during exercise, and within the “Straight Egyptian” sub-group, for facial morphology. Finally, we found strong evidence for recent interbreeding of Thoroughbreds with Arabians used for flat-racing competitions. Overall, our data support an origin of the Arabian horse in the Fertile Crescent and ample global genetic diversity across the breed.