what is stringhalt in horses

Stringhalt, or equine reflex hypertonia, is a neuromuscular condition that causes a gait abnormality characterized by involuntary, exaggerated upward movement of one or both of the hindlimbs. It looks like a jerk or hop, with the affected hindlimb(s) snapped up towards the abdomen. This generally occurs with every stride at the walk, but can lessen at the trot and is usually absent at the canter. Stringhalt is not a reaction to pain, so affected horses are not necessarily uncomfortable. There are two major categories of stringhalt: acquired (Australian, plant-associated, pasture-associated, or sporadic) and idiopathic (true, classic or atypical) . The acquired form results from plant (often flatweed/false dandelion, Hypochaeris radicata) toxicity, often occurs as an outbreak in horses on pasture in late summer or fall, and is usually temporary. The idiopathic form is of an unknown cause and may occur in one or both legs (unilateral or bilateral) . Diagnosis is based on clinical signs but can be confirmed by electromyography. There is no definitive treatment for stringhalt, and some horses may recover spontaneously. In cases of plant poisoning or intoxication, horses should be removed from areas containing the toxic plant. Surgical resection of part of the muscle and tendon (myotenectomy) of the lateral digital extensor at the level of the hock may be performed in severe cases.