Emerging Trends In Equine DNA

Appraising a horse by physical appearance alone is a thing of the past in the world of equine breeding and selling. Thanks to rapidly changing advancements in technology, horse owners, breeders and enthusiasts can learn more about their horses now than ever before.

Tests evaluating an animal’s deoxyribonucleic acid (DNA), can identify the individual markers of a horse and unveil the genetic code that determines both the horse’s health and physical appearance.

“The most widely available DNA tests in horses look for single gene diseases,” said Molly McCue, DVM, MS, PhD, American College of Veterinary Internal Medicine diplomate and University of Minnesota (UM) College of Veterinary Medicine associate professor. “With the increase in emerging genetic tools, I see DNA testing expanding rapidly. We used to be able to test for seven genetic mutations in horses, and now we can identify nearly 20. This information allows owners to make more informed breeding and management decisions.”

DNA testing requirements are very breed specific. For example, European breed associations require testing on most of their registered horses, and while it’s great to identify any disease carriers, McCue said issues can arise when breeders start limiting gene pools because of test results.

“Knowledge is power, and genetic testing is a great way to learn more about a horse and specifically test for certain diseases,” said McCue. “However, some associations choose to eliminate genetic lines altogether if the horse is a carrier of a disease. This can be a problem because as we try to eliminate some of these diseases, we lose genetic diversity and increase the risk of inbreeding depression, which is the accumulation of deleterious genetic mutations.”

In short, breeders often select for a typical trait, and the opposite side of that is a loss of genetic diversity. McCue said DNA testing is a hot button issue in the industry right now.

“Many owners worry that information about their horses learned from DNA tests could have negative economic impacts,” she said. “I understand that concern, but I think educating horse owners and breeders about how to avoid the risks of recessive diseases and how to manage these horses if they are carriers would go a long ways toward easing those concerns.”

The American Quarter Horse Association (AQHA) currently offers a five-panel test to determine if a Quarter Horse is a carrier of five genetic diseases including glycogen branching enzyme deficiency (GBED), hereditary equine regional dermal asthenia (HERDA), hyperkalemic periodic paralysis (HYPP), malignant hyperthermia (MH) and polysaccharide storage myopathy type 1(PSSM).

“We require all stallions to be tested with the five-panel disease test,” said Tammy Canida, AQHA director of registration operations. “AQHA began requiring stallions to be tested in 2014. It allows owners to know if horses are carriers of these diseases so they can make responsible decisions for their breeding programs.”

These equine diseases can affect a horse in a myriad of ways. Some can severely impact a horse’s health and even be terminal, while other symptoms are fairly mild and can be managed to lessen the effects.

McCue has spent her veterinary career studying these diseases and holds a patent on the PSSM test. Her passion for American Quarter Horses is what drives her to improve things for the breed and address some of the misconceptions out there regarding these diseases.

“PSSM can be managed with diet and exercise,” said McCue. “However, without these genetic tests, a horse owner wouldn’t know that management of a disease was necessary.”

The panel test can also be run in conjunction with the DNA test required for most breeding stock to verify parentage.

“DNA testing provides us with a tool to help fulfill one of AQHA’s mission statements to preserve the integrity of the breed,” said Canida.

DNA kits with hair samples are sent to the University of California-Davis Veterinary Genetics Laboratory, and AQHA notifies the owner once results are in and updates the horse’s records with its registration information.

The American Paint Horse Association’s (APHA) has its own set of rules when it comes to DNA testing.

According to Jessica Hein, APHA senior director of member care and publications, “APHA requires stallions used for breeding to have their DNA on file before any offspring can be registered. Foals that are the result of transported semen or frozen semen breeding are required to be parentage verified through DNA testing.”

Foals resulting from embryo, vitrified embryo or oocyte transfer must be parentage verified. Additionally, race horses are required to be parentage verified prior to being tattooed.

Coat color tests are also common with Paint Horses, as well. Available coat color tests include red factor, agouti, cream, pearl, champagne, dun, silver, gray, tobiano, frame overo, splash white, dominant white and Sabino 1.

APHA also offers disease diagnostic tests to determine if a horse is a carrier of HERDA, HYPP, GBED, MH, PSSM1 and/or OLWS.

“We advocate for genetic health panel testing,” said Hein. “This year, our board of directors passed a measure which goes into effect on the first of January that will require all stallions to have a genetic health panel on file in order for their foals resulting from breedings after January 1, 2018, to be eligible for registration. The genetic health panel costs $125, and there’s an option for a comprehensive test that includes both genetic health and color panel tests for $139.”

While equine DNA testing has been around for decades, the ability to test for a wider range of traits is still in its infancy. While the UM laboratory McCue works at has traditionally focused on genetic disease testing, she said it’s now split 50-50 from identifying disease mutations to determining genetic performance markers similar to cattle.

“Looking at halter horses, many descendants of Impressive are carriers of HYPP, although there’s no proof he has the mutation,” said McCue. “Because of this, there’s the belief that HYPP makes winners, despite there being no scientific evidence to prove this. However, if we could identify the performance markers that did make Impressive a winner, we could make breeding decisions by selecting those specific traits for future offspring. If we can choose to breed for both the positive traits and the things we want to avoid, moving forward over time, we can use this information to keep horses healthy, maintain genetic diversity and improve our breeding decisions.”

Published in 2017 Black Hills Stock Show® Horse Sale Catalog and Stallion Row Showcase