What is HERDA?
HERDA or Hereditary Equine Regional Dermal Asthenia is a rapidly emerging genetic disease of Quarter Horses and horses of Quarter Horse lineage, such as Paints and Appaloosas. Affected horses develop severe lacerations, hematomas, and seromas from minor trauma, frequently resulting in disfiguring scars. Due to their persistent wounds, most horses cannot be ridden or shown competitively and are humanely euthanized. Many horses affected with HERDA are often not diagnosed until they are 1-2 years of age, but severely affected horses may develop signs shortly after birth. Symptoms include ‘stretchy’ skin that feels ‘mushy’ or ‘doughy’ to the touch.
Contrary to what the name implies, this disease affects tissues throughout the horse’s body - documented issues include weak heart valves, tendons and a higher incidence of eye ulcers. Based on research vet's current understanding of collagen production, they predict that the production of all fibrillar collagens will be altered in HERDA-affected horses. These include collagens in skin as well as tendons, ligaments, bone, joint capsule, supporting tissue around blood vessels, eye structures and cartilage (although different tissues/types of fibrillar collagen may be affected to different extents).
HERDA descends through Poco Bueno who most commonly appears in the 7th or 8th generation back in horses at risk. Therefore, just looking at the pedigree on registration papers will not be adequate to determine if a horse is at risk. If two carrier horses are bred, the resulting foal has a 25% chance of being affected. Therefore, it is ill advised to breed a carrier horse to another carrier horse. Breeding a normal horse to a carrier horse will not produce an affected horse, but will have a 50% chance of producing another carrier horse. A DNA test is available at the University of California, Davis. (Information provided by Dr. Rashmir and Dr. Winand)