HERDA, a devastating genetic condition causing severe skin tearing and wounds, has been traced to the Poco Bueno bloodlines of the American Quarter Horse. The prevalence of this sire line in many Quarter Horses, Paints and Appaloosas makes testing for the HERDA mutation a vital tool in preventing the occurance of this fatal disease.

In the past few years, a new genetic threat to breeding horses has been identified. HERDA, or Hereditary Equine Regional Dermal Asthenia, is a debilitating and almost always fatal condition of the skin, deeply affecting the Quarter Horse, Paint and Appaloosa breeds.

HERDA, also known as Hyperelastosis Cutis, is an inherited disease that causes the skin along the horses back and neck to stretch and tear easily. In affected horses, a genetic mutation weakens the collagen fibers that hold the layers of the skin together. Skin rips and tears easily, and often heals with extensive scarring. Exposure to sun can cause the skin to peel and tear, and in extreme cases, the skin can split along the entire length of the horses back, and even roll down the sides.

Although horses carry this defect from birth, they often do not show signs of the disease until being broke to ride. The rubbing of the saddle on their skin causes severe sores and wounds along their back. New areas of damage occur continuously, and without trauma, and are a constant source of infection and extreme pain for the horse.

There is no cure for HERDA, and horses diagnosed with this condition are generally euthanized, as cannot be ridden, and cannot be used for breeding. The general expected lifespan for a horse with HERDA is 2-4 years.

When HERDA first appeared in the Cutting and Reining lines of Quarter Horses, the horse industry quickly mobilized to find the cause. Close scrutiny of the pedigrees of affected horses began to show a pattern- a full 95% of horses affected with HERDA trace back to the great Quarter Horse sire, Poco Bueno. The other 5% of horses trace to Poco Bueno and his full brothers sire, King. Studies from Mississippi State, Cornell and other major universities back up this finding.

The incidence of HERDA has not been limited to the American Quarter Horse. Breeds with extensive Quarter Horse lineage, such as Paint and Appaloosas, are also affected. A Champion in the show ring, Poco Bueno made a substantial mark on the founding of these breeds, and his progeny have been champions in all disciplines, from Reining and Cutting, to Western Pleasure and Racing.

While there are millions of horses that can trace their lineage back to Poco Bueno, not all of these offspring are carriers of the defect. Because HERDA has an autosomal recessive mode of inheritance, it is important to know if your horse carries the mutation, if you intend to breed. If a mare and stallion are both carriers of the mutation, they have a 25% chance of having an affected foal. Breeding a carrier horse to a normal horse will not produce a HERDA foal, but the foal will have a 50% chance of becoming a carrier.

In 2007, UC Davis and Cornell University began offering a DNA test to detect carrier status of the mutation. Early testing within the first few months of showed that approximately 15% of registered Quarter Horses, Paints and Appaloosas were confirmed carriers. Several prominent breeding stallions were also identified as carriers, and their owners notified.

The test can be performed on blood or hair samples, and can definitively identify normal, carrier, and affected horses, as well as testing foals at birth.

By identifying carrier horses, this test has enabled breeders to make informed decisions about their breeding choices. By eliminating pairings between carrier parents, the incidence of HERDA affected foals can be all but stopped. Due to the prominence of Poco Bueno in today's popular bloodlines, it is vital for this valuable test to become a mainstay of the horse industry. Just as testing for other genetic disorders, such as HYPP, has become a mainstay of the horse world, testing for HERDA will prevent the occurrence of this devastating disease.

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