What DNA tests can—and can’t— tell you about equine ancestry
Q:
I have been following Dr. Deb Bennett’s “Conformation Insights” articles in EQUUS with great interest. I was motivated to learn my horse’s ancestry and sent samples of his
DNA to Texas A&M’s Animal Genetics Laboratory for analysis.
The results came back with the first three breed markers being Selle Francais, Holsteiner and Hanoverian. This horse is a “mustang,” born wild in the Spring Creek Basin herd area of the Disappointment Valley in Colorado. He was gathered and adopted in 2011 as a yearling. My question is---how can this be possible? Is DNA testing really valid?
Lynda Larsen
Cortez, Colorado
Editor’s Note: Because of the many facets to this question, Deb Bennett, PhD, not only provided an answer but suggested that we enlist the assistance of other experts in the field of equine breeds and genetics. What follows are each of their perspectives on this question.
A:
First, the results you obtained ---no matter from how reputable a laboratory---could be bogus because of error. Samples can get mixed up or mislabeled. Even with the latest methods, I would not feel confident in DNA results returned from a single laboratory, but would submit to at least three reliable places and then compare all the results.
Second, the DNA analysis might be right on. Have you inquired as to whether anyone else has had a “mustang” from the same source herd and gathering tested? Many feral horses “born in the wild” in our country are not entirely of Iberian
DNA analysis showed that the feral Spring Creek Basin herd is genetically most similar to Quarter Horses, Thoroughbreds and Warmbloods.
origin, and neither the Bureau of Land
Management (BLM) nor any private agency is obligated to guarantee to adopters that they are “Spanish” to any degree.
Much depends upon how many domestic horses of other breeds were turned out on the range on which your animal was born. It’s entirely possible that your animal was sired or mothered by a horse of non-Iberian origin. Many of horses on the range were simply unwanted or escaped domestic livestock. Whereas escapes date back to the early 1600s with Juan de Oñate’s colonization of Santa Fe, horses have continued to escape or be deliberately turned loose onto range at all times since. After the middle of the 19th century, most of those horses were not of Iberian origin.
Deb Bennett, PhD
Director, Equine Studies Institute Livingston, California
A:
This does get tricky. The basic “problem” is that the breed assignments are done by relative frequencies of specific allele combinations more than the absence or presence of specific individual alleles. Because most horse breeds share a great many of these, that means that few horse breeds have little bits of this information that are absolutely unique to them. The consequence of this is that some combinations that can pop up are more likely to be typical of some other breed than the one actually involved.
So, while the technique works out well on average, it can be misleading for some very valid reasons related to procedure when used for a specific few animals.
D. Phillip Sponenberg, DVM,
PhD, ACT (Honorary)
Professor, Pathology and Genetics Virginia-Maryland College of
Veterinary Medicine
Blacksburg, Virginia
A:
The DNA ancestry testing done by the Animal Genetics Laboratory at Texas A&M University is designed to give owners an idea of the breed or breeds might be in the background of a horse of unknown ancestry. The interpretation of results can be difficult and complex, but a pretty good explanation is provided on the facility’s website: vetmed.tamu. edu/animalgenetics.
The results from this horse’s ancestry test can easily be confusing ---or even make no sense to an owner ---but they are not unreasonable if you understand what the test result actually means. In this case the owner expects the horse to show up with “Spanish” ancestry because it is a mustang, but instead the test suggested that the horse’s ancestors were from European Warmblood breeds.
Both Drs. Bennett and Sponenberg gave reasonable explanations to the question “How could this be?” and “Is DNA testing really valid?” but I believe there’s even more to the answer.
First, although laboratory error is always a possibility because this work is done by humans, all laboratories that do equine DNA testing have very strict quality control and very seldom make errors.
Also, sending a sample to three laboratories is overkill unless the first two come up with different types.