PROTECT HERDA HORSES FROM THE SUN

A good way to help horses with the devastating skin condition known as hereditary equine regional dermal asthenia (HERDA) is to limit their exposure to sunlight, according to a new study from the Laboratory for Comparative Orthopaedic Research at Michigan State University.

HERDA, which is passed along through certain Quarter Horse bloodlines, leads to extremely fragile skin that easily tears. It is an autosomal recessive disorder, meaning that horses who inherit only a single copy of the defective gene are carriers who won’t develop the problem; however, when two carriers are mated, their offspring have a one-in-four chance of developing the condition. Severely affected horses can’t be ridden because even normal pressure from tack creates large, open wounds that do not heal. Previous research has shown that HERDA is a form of Ehlers-Danlos syndrome, a group of genetic diseases caused by mutations in the genes that control collagen formation.

The risks of sun exposure for HERDA horses have been recognized anecdotally for some time, says Ann Rashmir-Raven, DVM, MS, DACVS, PGCVE. “If you speak to people who are familiar with these bloodlines and this condition, you’ll learn that keeping these horses out of the sunlight

Reference: improves their skin. And I personally observed that when we’d get horses with the condition at the research clinic, their skin would improve while they were kept indoors during quarantine.”

Building on this knowledge, the Michigan researchers began investigating the role that exposure to UV light may have on the condition. “When human skin is exposed to light, the enzyme known as collagenase is upregulated,” explains Rashmir-Raven. “Collagenase eats collagen. To some degree, this can be helpful; in order for skin to repair itself it needs collagenase. But too much sunlight can push this to the point where it’s destructive. If you have friends who sunbathe regularly, you notice their skin is quite different by the time they are 50. That’s in part because the UV light from the sun increases collagenase activity.”

For the study, researchers took full-thickness skin samples from various anatomical locations on seven horses diagnosed with HERDA and six normal ones. A total of 24 samples were taken from each horse, and half were incubated in a collagenase solution to produce the same effect that exposure to sunlight would. Researchers then used a machine to test all of the samples for stretchability.

“We were measuring how