Genetics: The New Frontier: Part 2

The equine genome map is as important to the future of horses as the development of antibiotics was 45 years ago.

This is the second of a four-part series. Need to review Part 1?

Recently when studying osteochondrosis (OCD) in a band of Kentucky Thoroughbred yearlings, Dr. Alicia Bertone found an interesting development: The gene chip showed that those horses in the study affected by the disease had suppressed activity of the retinoic acid pathways, which is important for cell division. (Retinoic acid is used as a human dermatological treatment known commercially as Retin-A.) This discovery should spark an investigation into the role of retinoic acid in OCD, a possibility never before considered.

As a practical implementation of the gene-chip technology, Dr. Bertone speculates that an owner could routinely test weanlings – even if they appeared to be normal – to determine whether their genes were expressing the signature for OCD.

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“If you know it early enough, you can adjust the horse’s diet, how fast you ask it to grow up and how much exercise it gets until it is out of the woods with that problem,” she says.

Hereditary Equine Regional Dermal Asthenia (HERDA) is a skin disease prevalent in cutting horses that is traceable to the Poco Bueno line. The disease is caused by an autosomal recessive gene, which means horses that have the gene can be carriers without being affected. As long as a carrier is bred to stock that is free of the HERDA gene, the trait remains recessive and the offspring do not develop the disease. However, if two carriers of the gene are mated, the gene can become expressed and the mare has a 25 percent chance of producing an affected foal.

HERDA is caused by a defect in the collagen, which causes it to give disorganized fibers that create a fragile attachment of the skin. Even mild contact with the skin on an affected horse’s back causes it to dislodge and peel away in large sheets, making these horses unusable. Most times, their owners decide to euthanize them.

Dr. Nena Winand, senior research associate in the department of molecular medicine at Cornell University, helped develop a test to identify horses with the HERDA gene. Test results, which can be obtained using blood or hair samples, declare the horse is “normal,” “carrier” or “affected.” Of 1,200 Quarter Horses, Paints, and Appaloosas tested, 170 or 14 percent were declared carriers.

“We could totally do away with affected horses if you don’t breed carrier to carrier or carriers to affected horses,” says Dr. Ann Rashmir, associate professor of equine surgery and medicine at Mississippi State University who is the principle investigator into HERDA. “So the application for this test would be that you would know the day a baby is born whether or not it has the genetic trait, or you could prevent that baby even from being born.”

Stay tuned for the third part of this four-part series.

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