Conditions or ailments that are the cause of a problem that you see - your observation.

Your vet may diagnose

Hereditary Equine Regional Dermal Asthenia, HERDA

Synonyms: Hyperelastosis Cutis


This is a heritable (genetic) skin disease seen in certain lines of American Quarter Horses and related breeds, and very rarely in other breeds. Most horses with the classic disease are related somewhere in their pedigree to Poco Bueno, the famous Quarter Horse sire. Cases of HERDA range from mild to severe.

HERDA is a disorder of connective tissue throughout the body, but is most obviously seen in the skin. Connective tissue becomes elastic and weak. It appears as overly stretchy skin usually noticed over the body and back, and particularly under the mane. The skin may tear easily, causing wounds to mysteriously appear.

Unexplainable wounds to the back develop after a horse with HERDA is placed under saddle. For this reason, they cannot be ridden. When pinched, the skin remains tented. Poor elastic recoil causes it to remain in tented ridges for longer than usual.

Genetic testing is being done to eliminate affected horses from the gene pool and definitive diagnosis requires the genetic test on a hair sample. The disease is caused by an autosomal recessive gene. This means that in order for a horse to show signs of disease, it must have gotten a copy of the gene from each parent. It must have two copies of the gene.

my vet's role


Prognosis is poor for severely affected horses. Depends on severity of disease.

For horses diagnosed with HERDA, new research suggests limiting their exposure to sunlight may help.

my role

Questions To Ask Your Vet:
  • Can I continue to use my horse for breeding if it has this condition or if it is a known carrier?
  • How severely affected is my horse?
  • What changes in my expectations and management are needed to care for my horse long-term?

Remove horses with the condition from the breeding population. DNA test horses with Poco Bueno anywhere in their lineage. This requires a test on a hair sample submitted to a genetics laboratory.

further reading & resources

Related References:

Rashmir-Raven, A., Lavagnino, M., Sedlak, A., Gardner, K. and Arnoczky, S. (2015), Increased susceptibility of skin from HERDA (Hereditary Equine Regional Dermal Asthenia)-affected horses to bacterial collagenase degradation: a potential contributing factor to the clinical signs of HERDA. Vet Dermatology, 26: 476–e111. doi: 10.1111/vde.12256.

Author: Doug Thal DVM Dipl. ABVP