Ocular Disease in Horses with HERDA: Study

In an eye-opening event, Mississippi State University researchers discovered that Quarter Horses diagnosed with the disease called hereditary equine regional dermal asthenia (HERDA) not only have skin defects but also important eye abnormalities.

HERDA is a recessive genetic disease of horses that results in fragile skin that tears easily and heals poorly.

"Recent studies have shown that HERDA is becoming increasingly prevalent in Quarter Horses," relayed Ann Rashmir-Raven, DVM, MS, Dipl. ACVS, associate professor of Large Animal Clinical Sciences at Michigan State University’s College of Veterinary Medicine.

"An estimated 28% of cutting horses are carriers of the gene responsible for HERDA," she added.

In humans with a similar disorder, Ehlers-Danlos Syndrome or EDS, various ocular disorders are present in addition to the changes in the skin.

To determine if horses with HERDA also have ocular changes, Rashmir-Raven and colleagues from Mississippi State University's College of Veterinary Medicine examined the eyes of 10 Quarter Horses with HERDA and 10 Quarter Horses without HERDA.

Key findings of the study were:

  • The thickness of the cornea (the outer surface of the eye) was significantly less in horses with HERDA;
  • Tear production was significantly greater in HERDA horses than in non-HERDA horses;
  • Microscopic analysis identified zones of disorganized, haphazardly-arranged collagen fibrils (connective tissue) in HERDA horses but not in non-HERDA control horses; and
  • Corneal ulcers were more common in horses with HERDA.

According to Rashmir-Raven, "This is the first study to show that abnormalities in horses with HERDA are not limited to the skin. Considering the high prevalence of HERDA in some populations of Quarter Horses it is important to assess the eyes of these horses."

Rashmir-Raven indicated that research is ongoing at Michigan State University.

The study, "Ocular findings in Quarter Horses with hereditary equine regional dermal asthenia," was published in the August 1, 2010 edition of the Journal of the American Veterinary Medical Association. The abstract is available for free on PubMed.

About the Author

Stacey Oke, DVM, MSc

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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