HC/HERDA Research

In 2004, the newly clarified hereditary disease hyperelastosis cutis (HC), also known as hereditary equine regional dermal asthenia (HERDA), received much attention. One of the leading researchers into this disease is Ann Rashmir-Raven, DVM, MS, Dipl. ACVS, associate professor in the department of clinical sciences at the Mississippi State University (MSU) College of Veterinary Medicine. She gave an update on HC at the 50th annual American Association of Equine Practitioners (AAEP) Convention in Denver, Colo., Dec. 4-8, 2004.

As a reminder, she outlined the specifics of the disease, which is an autosomal recessive connective tissue disorder of economic importance in Quarter Horses and horses of Quarter Horse lineage, she said. It occurs most frequently in popular cutting horse bloodlines. (She noted that in the cutting horse industry alone, 12 of the top 100 cutting sires are confirmed carriers. These 12 stallions have sired about 7,579 total registered offspring, and approximately 3,790 will be carriers.)

Affected horses have extremely fragile skin that tears easily and exhibits impaired healing. In horses with HC, the skin separates between the deep and superficial dermis. There is no cure. A DNA test for carrier identification is not yet available, and therefore, managed breeding strategy is currently the only option for reducing the incidence of HC.

Rashmir-Raven has traced the defects to Poco Bueno and his immediate ancestors. She said Poco Bueno's full brothers Captain Jess and Old Grandad also were likely carriers. Poco Bueno's sire, King, has genetic ties to 4% of known affected horses. In pedigree evaluation, having Poco Bueno or King in both the top and bottom of a pedigree within six generations has a significant correlation with the occurrence of HC.

Rashmir-Raven discussed a study of 44 affected horses. She has up to 24 affected horses in her breeding herd at any given time; 15 additional horses were evaluated then euthanatized, and a handful of client animals continue to be maintained by their owners.  In addition, she has evaluated 7 confirmed carriers and over 150 additional pedigrees of affected animals from the United States, Canada, Brazil, and Europe.

She noted that in comparison to other horse populations, HC horses had higher incidences of cryptorchidism, more colic, more respiratory disease, more ophthalmic diseases (including uveitis), and the foals were not as thrifty.

Rashmir-Raven said while there is no known cure for HC, palliative therapy can improve the quality of the affected horse's life. Horses are less apt to develop lesions during the winter; thus suggesting, said Rashmir-Raven, that a solar- or heat-related stress to the skin that might contribute to the development or progression of the lesions. She noted that the skin of affected horses improved significantly when they were kept indoors and away from other horses.

Recognizing more subtly affected horses will be important until a DNA test can be developed to positively identify affected and carrier horses.

In the question and answer session, Rashmir-Raven was asked about her comments on the use of Cosequin (a joint health supplement) for HC horses. She said that there was anecdotal evidence from owners of affected horses that giving Cosequin was helpful. There is also some evidence that human skin might benefit from the product. Recent studies on fibroblasts, the cells that make connective tissue like collagen, suggest that there might be some skin benefit with Cosequin usage.

About the Author

Kimberly S. Brown

Kimberly S. Brown was the Publisher/Editor of The Horse: Your Guide To Equine Health Care from June 2008 to March 2010, and she served in various positions at Blood-Horse Publications since 1980.

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