One of the hard and fast rules of the Thoroughbred breed is that a registered horse must have descended from one of three foundation sires: The Darley Arabian, the Godolphin Arabian, or the Byerley Turk. A study in the journal Scientific Reports suggests those stallions might not have been Arabians at all.
The study, led by Ben Shykind of Prevail Therapeutics and Elissa J. Cosgrove and Raheleh Sadeghi of Cornell University examined the genetic makeup of 378 Arabian horses from 12 different countries to see how Arabians related to other horse breeds and found “no significant genomic contribution of the Arabian breed to the Thoroughbred racehorse, including Y chromosome ancestry.”
However, the study did find “strong evidence” of Thoroughbred blood in recent generations for Arabians used in flat racing.
The three foundation stallions that are the basis of the modern Thoroughbred were imported to England from the Middle East in the early decades of the 1700s. However, analysis of Y chromosome haplotypes (genes inherited from a single parent) for the Darley Arabian found his lineage actually traces back to the extinct Turkoman horse, an ancient breed from the Middle East and Central Asia under the same grouping of “Oriental Horse” breeds as Arabians, but a different offshoot.
The study does not doubt the existence of Thomas Darley's stallion purchased from the Middle East who went on to shape the modern Thoroughbred, but it does suggest that “its breed was likely of yet unknown genetic origin,” and that the horse's nomenclature carried on the idea that the horse was indeed an Arabian, thus his descendants sprung from that breed. Doubts about the true genetic origin of the Thoroughbred breed, it is noted in the study, were brought up two decades ago in Alexander Mackay-Smith's book “Speed and the Thoroughbred: The Complete History.”
In plotting the 378 horses included in the study by their use – including endurance racing, flat racing, and showing – the 34 Arabians used for flat racing shared the most genetic makeup with Thoroughbreds, while those bred for show purposes traced back to the Egyptian branch of the Arabian breed, and endurance runners tracked with the Polish wing. The researchers found genomic segments in racing Arabians tracing back to Thoroughbreds ranging from two percent up to 62 percent, with some near-full length chromosomes coming from Thoroughbreds.
Five of the 10 male Arabian racehorses traced directly back to the Byerley Turk though their Y chomosomes. Another three shared Whalebone, a significant Thoroughbred sire in the early 1800s, as a common ancestor.
“The presence of Thoroughbred-specific Y chromosome haplogroups among Arabian racehorses indicates that the large chromosomal blocks of Thoroughbred origin detected in flat racing Arabian horses are likely derived, at least in part, from crosses with Thoroughbred stallions that occurred after the emergence of the “Whalebone” haplotype in the 1800s,” the study reads.
Read more about the study, Genome Diversity and the Origin of the Arabian Horse, here.
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