Some skin conditions in horses are caused by fungus and bacteria, while others are caused by external factors such as beddings or medications. However, some dermatological issues appear in horses courtesy of genetics. At the 2011 Western Veterinary Conference, held Feb. 20-24 in Las Vegas, Nev., Ann Rashmir-Raven, DVM, MS, Dipl. ACVS, of Michigan State University, presented on a few of the most common equine skin disorders that have a genetic basis.

Rashmir-Raven explained that hereditary skin disorders are most commonly autosomal recessive traits, meaning that each of the foal’s parents, which appear normal, carries one normal allele and one defective allele. When both parents pass their defective alleles on to the foal the foal ends up with a pair of defective alleles, triggering disease expression.

She stressed that in most cases these autosomal recessive genetic disorders–which remain incurable and sometimes untreatable–can be prevented with careful breeding planning. Many DNA tests are now available to help an owner determine whether a mare or stallion is a carrier of a specific genetic disorder, and Rashmir-Raven recommends obtaining test results from both the mare and stallion to ensure two carriers are not bred (which would result in a 25% chance of a foal with the pair of defective alleles being born)