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Researchers study equine skin disease
MISSISSIPPI STATE -- A team of Mississippi State University veterinary researchers hopes to find the genetic defect responsible for a devastating skin disease in American quarter horses.
Though success is likely several breeding seasons down the road, Dr. Cyprianna Swiderski, an assistant professor studying hyperelastosis cutis, said the overriding goal of the research in MSU's College of Veterinary Medicine is to learn to manage this disease in the same way that has been done with human genetic diseases. Hyperelastosis cutis causes quarter horses' skin to weaken, wound easily and heal poorly with disfiguring scars.
"At this point, we know the disease is inherited. Our primary objective is to identify the defective gene or genes and develop a test that will identify carrier and affected animals," Swiderski said. "This will allow us to genetically manage the population and dilute the defect to the point that the disease is no longer such a widespread problem, while maintaining the desirable genetic traits of these tremendous athletes."
Because horses are expensive to maintain in research herds, Swiderski said these goals will only be realized with the financial support of quarter horse owners.
HC is believed to be a genetic connective tissue defect that causes a horse's skin to be unusually loose. Although the disease is generally present at or shortly after birth, owners frequently do not notice problems until the horse goes into training, typically around age 2.
Trauma from the saddle imprint can cause open sores, hematomas and significant pain.
Dr. Ann Rashmir-Raven, an associate professor in MSU's veterinary college, said her research shows that years of breeding closely related American quarter horses to obtain desirable traits actually caused this devastating skin disease in the breed.
"All of the horses diagnosed with HC are related," Rashmir said. "As is common in breeding programs, closely related horses were bred in the hopes of producing better-performing horses. Because of the popularity of sires that are or were carriers and the use of assisted reproductive technologies, it is likely that the HC gene is present in thousands of horses."
Like many other owners of HC-affected horses, Cindy Lyles of Haslet, Texas, was devastated to discover her twin colts suffered from the disease. At first she noticed the colts frequently developed unexplained skin injuries, and she spent months trying to solve the problem.
"We kept thinking they were just rambunctious -- rearing up on each other and biting, getting nicks and cuts," she said. "We tried separating them in different pastures so they couldn't hurt each other. Then one got hurt on his lower leg, and that didn't heal for a couple months and was really nasty."
Lyles' veterinarian suspected HC was responsible for the colts' injuries and sent a skin biopsy to Rashmir. In April, Cindy and her husband Keith donated both of the colts to Rashmir's research project. The grief they have suffered makes the Lyles reluctant to breed their mare again.
"This has been like losing one of our kids to a terminal illness. I'm not a big breeder -- these colts were in my backyard," Lyles said. "I'm not going to breed anymore until there's a DNA test that can assure me I'm not breeding to a carrier."
Rashmir and Swiderski are studying a group of hyperelastosis cutis-affected horses housed at the CVM. Along with two veterinary students, Ben Nabors and Ryan Butler, they are evaluating numerous aspects of this disease.
"We have a breeding trial under way that is confirming that HC has an autosomal recessive mode of inheritance, which means that both parent horses must carry the recessive gene for the offspring to be afflicted," Rashmir said. "A horse that is an HC gene carrier is never affected with the disease -- it is clinically normal and shows no signs of the disease. However, when two carriers are mated, there is a 25 percent chance the offspring will have HC."
Rashmir said the research project is evaluating foals for early signs of HC. That process involves documenting changes in skin biochemistry, thermography and ultrasonography, in addition to other forms of screening.
"No one has ever documented what happens in affected horses," she said.
There is no cure for this genetic disease, so the focus now is on educating owners of
quarter horses. The researchers say it is imperative that owners consider this disease when breeding related animals.
"It's not the horses' fault -- it's the way we have bred them," Rashmir said. "Many of these horses have been, and are, wonderful athletes and though they are carriers, have no outward signs of the disease. Only through responsible mating will we control this disease."
MSU's veterinary college is facilitating that process by offering pedigree screenings. Horse owners can send pedigrees involving potential matings to Rashmir and she will analyze them and determine the degree of probability of the offspring inheriting either the gene or the disease itself. A $25 fee per eight-generation pedigree goes directly to the HC Research Fund at MSU.
Contact: Dr. Ann Rashmir-Raven, (662) 325-1413