It’s a disturbing and distressing sight: You’re backing your horse when one hind leg jerks forward and upward, nearly clipping his abdomen. It’s the same every time you back your horse–this strange movement where his leg snaps up toward his belly. There’s no mistaking it: Your horse has stringhalt.

A neurologic disorder, stringhalt is an involuntary, exaggerated flexion of the hock that can affect one or both hind limbs. There appears to be three different types:

Classic or true stringhalt is an idiopathic (of unknown cause) disease. “Classic stringhalt occurs as isolated cases,” explains Kent Carter, DVM, MS, professor of medicine, section chief of internal medicine, and a lameness specialist at Texas A&M University. “You can have a whole herd of horses with just one horse getting it. There is no known cause; the horse just starts developing this gait.”

No environmental or nutritional relationship has been detected with classic stringhalt, and there are no apparent predispositions to breed or activity. However, classic stringhalt tends to affect adult horses and not youngsters. Carter notes that classic stringhalt is fairly uncommon, at least in his area.

Australian stringhalt (ASH) occurs in both hind legs, and it has also been seen in horses in the United States. ASH often affects more than one horse in a herd (average incidence is about 10-15% of a group), primarily occurs in late summer or autumn, and is observed in horses which are turned out in weedy pastures.

Says Peter J. Huntington, BVSc (Hons), MACVSc, MRCVS, a long-time rese