Hereditary Equine Regional Dermal Asthenia (HERDA)

HERDA is a skin condition that is characterized by hyperextensible (more elastic than normal) skin, severe scarring, and open wounds along the back of affected horses. HERDA causes collagen between skin layers to not form properly, resulting in a horse that is easily injured.

Collagen is important in connective tissues throughout the body including components in the eyes, heart, tendons, cartilage, and skin.

While affected horses appear normal at birth, they may notice more serious nicks and scrapes than other horses their age which will be slow to heal, often resulting in disfiguring scars. Most affected horses are not identified until they are started under saddle. The pressure of saddling often leaves wrinkly skin or large open wounds. Sunlight is suspected to increase damage to collagen thus making the top of the horse more effected (i.e. top of the neck, back, and rump), which is more exposed to UV rays. Most horses affected by HERDA are euthanized due to slow healing injuries.

HERDA is a recessive mutation. This means that your horse must inherit TWO copies to be affected. A horse that only inherits one copy, is known as a carrier, and will appear normal and will not experience any symptoms caused by this mutation.

Approximately 3.5% of all quarter horses are carriers, with most cases found in cutting and cow horse disciplines. It is estimated that 28% of horses in these disciplines carry one copy of HERDA. Breeding horses should be tested to ensure risk of producing HERDA affected horses is minimized.


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