Study: Arabian DNA Reveals Diversity, Other Breed Influences
Fraught with a paradoxical mix of praise and heavy criticism, the historically revered Arabian horse breed is considered “pure” as often as it’s considered “inbred.” But a new and far-reaching genomic study has revealed that, except for rare individual horses, Arabians are neither.

On the contrary, the Arabian breed is, for the most part, “genetically healthy,” with significant diversity in its genes, both in its homeland regions of the Middle East as well as abroad, said study author Samantha A. Brooks, PhD, of the Department of Animal Science in the Genetics Institute of the University of Florida, in Gainesville.

Plus, some sire lines aren’t nearly as pure as their breeders might think, she said. Their genomes reveal significant interbreeding, primarily with the Thoroughbred.

Good News or Bad News?

The international team of 19 researchers involved in this study came to clear conclusions: In at least one line of Arabians—the flat racing lines—many individual horses have mixed blood bearing the influence of other breeds, mainly the Thoroughbred, said Brooks. Some horses had up to 62% of their DNA coming from the Thoroughbred.

“We can see in the genetic signature that crossing with Thoroughbreds happened multiple times, and in some horses it happened over multiple generations,” she said, adding that this phenomenon is apparent in “many, many of our racehorses.”

It’s the kind of news breeders probably don’t want to hear, she said. Most Arabian breed registries—many of which record some of the oldest bloodlines in the equine world—strictly forbid adding other breeds to bloodlines. “Their paperwork tells them the horses have pure bloodlines,” said Brooks. “But the DNA doesn’t lie.”

That doesn’t make these horses “bad” or “impure,” or even “un-Arabian,” she said. “They’re still excellent athletes and beautiful animals.”

Some critics argue that the lines bearing Thoroughbred influence should be made public—something Brooks said her team refuses to do—and removed from the registry.

“Deregistering these horses all at once would not have good outcomes for the welfare of these beautiful animals,” she said. “And anyway, the issue is widespread enough that there wouldn’t be much of the racing population left. These data document a Thoroughbred breed influence much more expansive than most people realized. It’s just everywhere, really.”

A better solution, she said, would be working with some of the semantics. “These are still valuable athletic lines of horse, but they should be labeled appropriately,” she explained. “Maybe there can be subgroups with the appropriate national registries specific to the racing Arabians with genetically identified admixture. And then perhaps just not permit registering offspring of these horses back into the main studbook of traditional Arabian horses. I think they could do fantastically well in this type of system.”

Hundreds of Horses Genotyped

In their study, Brooks and her fellow researchers ran a broad panel of markers from across the whole genome on nearly 400 Arabian horses sampled in 12 countries. They also ran whole genome sequencing on 14 Arabian horses as well as a few Thoroughbreds and Standardbreds, and they pulled genomic data on hundreds of other Arabians and diverse horse breeds from previous DNA studies.

Brooks said they found that, for the most part, Arabian horses worldwide have strong genetic diversity. A few regions of the world have reduced diversity—possibly due to importing few horses or strong preferences for popular sires in some groups—and these populations could benefit from breed conservation programs based on genomic information of their breeding stock, she said. But for the most part, Arabians have a healthy level of genetic blends within their breed and should not be at risk of transmitting genetic diseases, despite popular belief.

One line of Arabians known as the Straight Egyptian Arabian, however, might run that risk, she explained. Some lines of Straight Egyptian Arabians, heralded as being the purest line of Arabians, appear to have genetic “bottlenecking,” indications of inbreeding from using small numbers of horses in their breeding programs.

“These valuable groups will benefit from careful management of their genomic diversity using modern, DNA-based tools rather than pedigrees,” Brooks said.

Thoroughbreds Weren’t Shaped by Arabians

Although it’s a common belief that Arabian horses strongly influenced the Thoroughbred breed, DNA analysis refutes this history, said Brooks.

“Certainly ‘history is as history’s written,’ right?” she said. “But in this case, the genomic analysis is clear: Thoroughbreds have very little influence from the modern Arabian breed. We can see some shared ancestry, but it’s a much smaller contribution than commonly believed.”

So what was the connection between Thoroughbreds and Arabia? It’s possible that there was a confusion between origin and breed when the Thoroughbred was being developed, she said. Perhaps the stallions were called Arabians simply because they were imported from the Middle East. It’s also possible that another breed called an Arabian existed but has since died out, she added. “We could be dealing with a population of horses that’s now extinct in the modern world or that we just haven’t been able to find and sample DNA from yet.”

The team’s research has helped better paint the picture of the world’s most celebrated horse breed, rich with romantic stories of its important role in culture and society, Brooks said.

“Peoples of the desert (in Bedouin) lived with these horses as part of the family,” she said. “These stories are idealized in Orientalist paintings from the 18th and 19th centuries featuring the Arabian horse relaxing in the family tent, alongside sighthounds, and they’re all there on the Oriental rug. This is unique imagery, and although it’s likely not perfectly historically accurate, it does artistically convey the genuine bond between this culture and their horse.”