HERDA in Horses: Hereditary Equine Regional Dermal Asthenia Explained
- HERDA is an inherited skin disorder seen most often in Quarter Horses and related breeds. It makes the skin unusually fragile, stretchy, slow to heal, and prone to painful tears.
- Signs often show up when a young horse starts training or wearing tack, especially over the back, shoulders, and neck where friction and pressure occur.
- There is no cure, but some horses can be managed with careful wound care, reduced trauma, and lifestyle changes. Many affected horses cannot be ridden safely.
- Diagnosis is confirmed with DNA testing, often using tail-hair roots. Carrier horses usually look normal but can pass the mutation to foals.
- Breeding prevention matters: HERDA is autosomal recessive, so two carriers can produce an affected foal.
What Is HERDA in Horses?
HERDA stands for hereditary equine regional dermal asthenia. It is an inherited connective tissue disorder that causes the skin to be abnormally fragile and stretchy. In affected horses, the collagen that helps hold skin layers together does not form normally, so the skin can separate, tear, and scar after minor rubbing or pressure.
This condition is seen most often in American Quarter Horses and related lines, especially those tied to certain cutting and cow-horse bloodlines. Clinical signs often become obvious when a horse is 2 to 4 years old and starts saddle training, because tack pressure and normal handling can trigger painful wounds over the back, shoulders, and neck.
HERDA is not contagious. It is a genetic disease, not an infection or allergy. Some horses are only mildly affected at first, while others develop severe skin sloughing, repeated wounds, and scarring that make riding unrealistic or unsafe.
Because quality of life can vary so much, the goal is not to force one path. Your vet can help you decide whether your horse may do best with conservative management as a pasture companion, more active wound care, or a broader quality-of-life plan.
Symptoms of HERDA in Horses
- Unusually stretchy or fragile skin
- Painful abrasions or open wounds over the back, shoulders, or neck
- Skin that sloughs or peels after minor friction from tack or handling
- Slow healing after routine scrapes or pressure sores
- Heavy scarring or thickened scar tissue in previously injured areas
- Seromas or hematomas under the skin after pressure or trauma
- Reluctance to be saddled or signs of back pain
- Possible corneal ulcers or eye irritation
Call your vet promptly if your horse develops repeated skin tears, painful sores under tack, delayed healing, or extensive scarring, especially if the horse is a young Quarter Horse or related breed. See your vet immediately if wounds are deep, contaminated, draining, foul-smelling, or if your horse seems very painful, depressed, or develops eye squinting or cloudiness. HERDA wounds can become difficult to manage, and early guidance may help reduce trauma, infection risk, and discomfort.
What Causes HERDA in Horses?
HERDA is caused by an inherited mutation that affects collagen formation. The mutation involves the PPIB gene and disrupts normal connective tissue structure, which is why the skin becomes weak and separates more easily than it should.
This disorder is autosomal recessive. That means an affected horse has inherited two copies of the mutation, one from each parent. Horses with only one copy are called carriers. Carriers usually do not show signs, but they can pass the mutation to offspring.
That inheritance pattern matters for breeding decisions. When two carriers are bred, each foal has a 25% chance of being affected, a 50% chance of being a carrier, and a 25% chance of being clear. Breeding a clear horse to a carrier will not produce an affected foal, but some foals may still be carriers.
HERDA has been reported most often in Quarter Horses and related breeds, and AQHA notes that about 3.5% of all Quarter Horses are carriers, with many cases linked to cutting and cow-horse lines. That does not mean every horse in those disciplines is affected. It means genetic testing is an important planning tool before breeding.
How Is HERDA in Horses Diagnosed?
Your vet will usually start with a history and physical exam. Recurrent skin injury over the back, shoulders, or neck in a young Quarter Horse or related breed raises suspicion, especially when lesions appear during training or after tack use. The pattern of fragile skin, slow healing, and scarring is often very suggestive.
A DNA test is the most direct way to confirm HERDA status. UC Davis Veterinary Genetics Laboratory lists HERDA as a Quarter Horse health test and notes that testing can be done from appropriate samples such as hair roots. Current listed lab fees are about $45 for one Quarter Horse health test or $100 for the six-test Quarter Horse health panel, not including collection, shipping, or your veterinary visit.
Results are typically reported as N/N for clear, N/HRD for carrier, and HRD/HRD for affected. DNA testing helps in two ways: it can support diagnosis in a horse with suspicious skin disease, and it can identify carriers before breeding.
In some horses, your vet may also recommend wound assessment, eye evaluation if corneal ulcers are suspected, or additional testing to rule out other causes of skin lesions. Diagnosis is not only about the gene result. It is also about understanding how severely the horse is affected and what level of daily management is realistic.
Treatment Options for HERDA in Horses
Spectrum of Care means you have options. Here are treatment tiers at different price points.
Budget-Conscious Care
- Veterinary exam and discussion of quality-of-life goals
- DNA test if not already confirmed
- Stopping riding and removing tack pressure from affected areas
- Basic wound cleaning, bandaging, and environmental changes to reduce friction
- Turnout or companion-horse management with careful skin monitoring
Recommended Standard Treatment
- Full veterinary exam with confirmed genetic diagnosis or review of prior results
- Structured wound-care plan with recheck visits
- Bandaging supplies, topical therapy, and pain-control plan as directed by your vet
- Evaluation for secondary infection and treatment when indicated
- Management changes such as padded environments, fly control, sun reduction, and retirement from tack work
Advanced / Critical Care
- Referral-level dermatology or equine hospital evaluation
- Intensive wound management for large skin defects or severe recurrent lesions
- Sedation, debridement, advanced bandaging, and hospitalization when needed
- Ophthalmic workup and treatment if corneal ulcers develop
- Broader quality-of-life planning, including discussion of long-term welfare and humane end-of-life options when suffering cannot be controlled
Cost estimates as of 2026-03. Actual costs vary by location, clinic, and individual case.
Questions to Ask Your Vet About HERDA in Horses
Bring these questions to your vet appointment to get the most out of your visit.
- Based on my horse’s lesions and history, how likely is HERDA versus another skin condition?
- Should we confirm this with a DNA test, and which sample does the lab need?
- Is my horse safe to ride, or should we retire them from tack use now?
- What wound-care routine do you recommend at home, and how often should bandages be changed?
- Are there signs of secondary infection or eye problems that would change the treatment plan?
- What daily management changes could reduce friction, sun exposure, and new skin injury?
- What is a realistic cost range for short-term care and for ongoing management over the next year?
- If this horse is a carrier or affected, what breeding decisions would you recommend?
How to Prevent HERDA in Horses
The most effective prevention is genetic screening before breeding. Because HERDA is recessive, affected foals can be prevented by avoiding carrier-to-carrier matings. UC Davis and AQHA both provide HERDA testing resources, and AQHA includes HERDA in its Quarter Horse genetic testing information.
If a horse is already affected, prevention shifts from breeding prevention to injury prevention. Your vet may recommend avoiding saddle work, reducing friction from blankets or tack, controlling flies, limiting sun exposure when skin is irritated, and checking the back and shoulders often for early sores.
Carrier horses usually look normal, so appearance alone is not enough. Testing breeding stock is the practical step that protects future foals. If one horse is a carrier, your vet can help you review breeding options that lower risk without making assumptions about the rest of the pedigree.
For pet parents managing an affected horse, prevention also means having a plan. Early wound care, fast response to new lesions, and regular quality-of-life check-ins with your vet can help keep some horses more comfortable over time.