Stringhalt is a neuromuscular condition in horses that causes an involuntary, exaggerated snapping-up of one or both hind legs during movement. Formally called equine reflex hypertonia, it produces a distinctive jerking or hopping gait that’s most visible at the walk. The condition ranges from a subtle extra lift of the hind leg to a dramatic snap where the hoof strikes the belly before being slammed back to the ground.
What Stringhalt Looks Like
The hallmark sign is hyperflexion of the hind limb: the leg gets pulled sharply upward toward the abdomen in an involuntary spasm, then forcefully planted back down. This happens with every stride at the walk but often lessens at the trot and typically disappears entirely at the canter. In severe cases, the horse may look like it’s hopping rather than walking normally.
Certain situations make the abnormal gait more obvious. Turning sharply, backing up, walking downhill, transitioning between gaits, or taking the first few steps after standing still all tend to exaggerate the jerking motion. The signs can appear suddenly and may affect one hind leg or both. Mild cases sometimes go unnoticed until the horse is asked to do something that provokes the spasm, while severe cases are unmistakable even on a straight line at the walk.
What Causes It
Stringhalt falls into two broad categories, and the distinction matters because the cause, outlook, and treatment differ significantly.
Classic (idiopathic) stringhalt affects a single hind limb and has no identifiable external cause. It can appear in any breed, at any age, and often seems to come out of nowhere. Because no toxin or injury can be pinpointed, this form is sometimes attributed to subtle nerve trauma, joint problems, or other localized issues in the affected leg.
Pasture-associated (Australian) stringhalt is a toxic form linked to grazing on pastures overrun with a weed called flatweed, or false dandelion (Hypochaeris radicata). It typically strikes during or after drought, when the weed dominates sparse pastures and the stress of dry conditions appears to increase the plant’s toxicity. Research has shown that stressed flatweed produces compounds that are directly toxic to nerve cells, causing damage similar to that of known plant-based neurotoxins. This form usually affects both hind legs and can strike multiple horses on the same property at the same time.
How the Nerve Damage Works
Regardless of the type, the underlying problem is damage to peripheral nerves, specifically the long nerve fibers that run from the spinal cord down to the muscles of the lower leg. The damage is classified as a distal axonopathy, meaning it’s worst at the far ends of the longest nerves. No lesions are found in the brain or spinal cord itself.
The nerves most affected are the peroneal and tibial nerves in the hind limbs, along with the recurrent laryngeal nerves in the throat (which is why severely affected horses occasionally have breathing noise as well). Because these nerves control specific muscles, the lateral digital extensor and long digital extensor muscles in the lower leg waste away over time. That muscle atrophy is often visible as a hollowing-out along the front and side of the cannon bone area.
The involuntary snapping motion likely results from damage to sensory receptors in the muscles and tendons. When the structures that normally regulate how far and how fast a muscle contracts are impaired, the brain receives garbled feedback and the leg fires in an exaggerated, spastic reflex.
How Veterinarians Diagnose It
Most cases are diagnosed by watching the horse walk, especially during situations that provoke the spasm: backing, sharp turns, or the first steps out of a stall. The gait pattern is distinctive enough that an experienced veterinarian can often identify stringhalt on visual exam alone.
When the cause is unclear or needs confirmation, electromyography (EMG) can be useful. In one documented case of classic stringhalt, EMG revealed abnormal electrical activity, specifically signs of denervation and hyperirritability, only in the lateral digital extensor muscle. The rest of the limb tested normal. This kind of targeted finding helps rule out other neurological conditions that might look similar.
In pasture-associated cases, a biopsy of the peroneal nerve and lateral digital extensor muscle can confirm the characteristic pattern of nerve fiber degeneration. Veterinarians also look at the bigger picture: multiple horses affected on the same pasture, the presence of flatweed, and recent drought conditions all point strongly toward the toxic form.
Treatment and Management
Treatment depends entirely on which type of stringhalt is involved.
For pasture-associated stringhalt, the first and most important step is removing the horse from the contaminated pasture and eliminating access to flatweed. Many horses improve gradually once the toxic exposure stops, though recovery can take weeks to months as damaged nerves slowly regenerate. Some horses recover fully; others retain a mild gait abnormality. Severe cases carry a less certain prognosis, particularly if significant muscle wasting has already set in.
An anti-seizure medication originally developed for humans has shown some benefit in managing symptoms. In a study of five horses with Australian stringhalt treated orally for two weeks, the medication produced improvement with only mild sedation and no signs of toxicity. It works by stabilizing overexcitable nerve membranes, which can reduce the involuntary spasms.
For classic stringhalt affecting a single leg, surgical removal of a portion of the lateral digital extensor tendon and muscle is sometimes performed. This procedure aims to eliminate the source of the abnormal reflex. Results vary: some horses return to normal movement, while others show only partial improvement.
Supportive care for both forms includes ensuring good nutrition, particularly adequate B vitamins and minerals that support nerve health. Controlled exercise may help maintain muscle mass in the affected limbs during recovery, though the specifics should be tailored to the individual horse’s severity.
Mild vs. Severe Cases
The spectrum of stringhalt is wide. At the mild end, a horse may show a slightly exaggerated hind leg lift that’s only noticeable when backing up or turning. These horses can often continue light work without much difficulty, and the condition may be intermittent.
At the severe end, every walking stride produces a violent snap of the leg toward the belly, followed by a forceful stomp. Severely affected horses struggle to move normally, may injure themselves from the repeated concussive impact, and can develop significant muscle wasting in the hind limbs. In extreme pasture-associated cases, horses may become unable to walk safely and require stall rest during the initial recovery period.
Cold weather, excitement, and periods of inactivity tend to worsen symptoms across all severity levels. Many owners notice the gait is worst first thing in the morning or after the horse has been standing in a stall, then improves somewhat with gentle movement.
Preventing Pasture-Associated Stringhalt
Since the toxic form is directly tied to flatweed exposure during drought, prevention centers on pasture management. Keeping pastures well maintained, controlling flatweed through mowing or herbicide before it dominates, and providing supplemental hay during dry spells so horses aren’t forced to graze weedy ground all reduce risk. If flatweed is prevalent and conditions are dry, moving horses to a clean pasture or drylot is the safest option. Outbreaks tend to cluster in late summer and autumn when drought stress peaks and pasture quality drops.