Q: I recently overheard someone talking about stringhalt and that a horse who has this can no longer compete in dressage. What exactly is stringhalt and can a horse who has been diagnosed with it still have a dressage career?
A: Stringhalt is an abnormal gait in horses, described as a sudden and exaggerated flexion of one or both rear limbs. There are two forms of stringhalt. One is called Australian stringhalt. The other is called classic stringhalt. Australian stringhalt affects both rear limbs simultaneously. It typically occurs in outbreaks among pastured horses who are consuming the noxious weed Hypochoerris radicata, commonly known as flatweed. Compounds in flatweed apparently affect some of the long sensory nerves to the horse’s rear limbs. Flatweed is native to Australia, but has been introduced to the U.S., and outbreaks here have been reported. Fortunately, the symptoms of Australian stringhalt typically resolve when the horse is removed from affected pastures.
Classic stringhalt affects only one rear limb. Just like Australian stringhalt, the limb will suddenly jerk upward, with a spasmodic motion toward the belly, usually when the horse is asked to move. The action may be mild or more exaggerated and violent. The cause of classic stringhalt is unknown. It is thought that classic stringhalt is the result of traumatic damage to sensory nerves to the extensor muscles of the rear limb. Unlike Australian stringhalt, this form of the condition is usually persistent and does not resolve.
Stringhalt is typically triggered when the horse is asked to move, either initiating the walk, turning, backing up or after a sudden stop. Excitement may trigger more exaggerated symptoms. In mild cases, limb flexion is only slightly affected and gaits above a walk may be normal.
Other conditions may cause a horse to abruptly lift a rear limb and look like stringhalt. A horse with significant pain in a rear foot, as from an abscess, may present in this manner. Pain originating from the hock or stifle may also cause a horse to suddenly jerk the limb up.
Stringhalt-like symptoms may also be present in horses affected by upward fixation of the patella, fibrotic myopathy, shivers or equine protozoal myeloencephalitis. Therefore, it’s important to perform a thorough exam with efforts to help determine a diagnosis of stringhalt.
For most horses with classic stringhalt the condition persists. A few have been reported to improve with time. Medical treatments have not been shown to be helpful. A surgical procedure that removes a portion of a muscle and tendon from the affected limb has reportedly helped some horses, but does not promise a consistent outcome.
The USDF describes the purpose of dressage as to develop the horse’s natural ability and willingness to work, making him calm, supple and attentive to his rider. Dressage judging penalizes any irregular gait or unevenness. A dressage horse affected by classic stringhalt is therefore handicapped. For horses increasingly affected by stringhalt, the uneven, exaggerated limb movement will significantly affect the gait and their capability will be limited. Dressage horses with mild symptoms of stringhalt may be able to perform at some levels, but are at a disadvantage.
Peter O’Halloran, DVM, is a member of the American Veterinary Medical Association, the American Association of Equine Practitioners, the Northeast Association of Equine Practitioners, the Maryland Veterinary Medical Association and the Virginia Association of Equine Practitioners. He is headquartered at Monocacy Equine Veterinary Associates in Dickerson, Maryland.