Stringhalt in Horses: Sudden Hindlimb Hyperflexion and Causes

Stringhalt is a movement disorder in horses that causes exaggerated, involuntary flexion of a hind limb during the forward swing of the stride. Pet parents often notice the leg snapping upward higher than expected, then returning to the ground abruptly. The change is usually most obvious at the walk and may stand out more when a horse is turned sharply or asked to back.

Stringhalt can affect one hind limb or both. Classical stringhalt is more often one-sided and may appear in an individual horse without an obvious herd problem. Bilateral stringhalt, often called Australian stringhalt, affects both hind limbs and has been associated with grazing certain weeds in dry or overgrazed pastures. Severity varies a lot. Some horses only show a mild, intermittent hitch, while others have dramatic hyperflexion that interferes with safe movement.

This condition is not the same as every other hind-end gait problem. Shivers, painful foot conditions, hock disease, and temporary irritation around the pastern can sometimes look similar. That is why a careful exam by your vet matters. The goal is not only to name the gait abnormality, but also to understand how much it affects comfort, safety, and future use.

The exact cause of classical stringhalt is still not fully understood. Research and pathology findings support involvement of the peripheral nerves, especially nerves serving the hind limb. In some horses, the problem appears as an isolated gait disorder affecting one leg. In others, a painful condition lower in the limb can create a temporary stringhalt-like movement, which is one reason your vet may look carefully at the hoof and pastern before settling on a diagnosis.

Bilateral or Australian stringhalt has been linked to toxic pasture exposure, especially when horses graze poor, dry, or overgrazed fields containing weeds such as flatweed. Cases are often reported in groups of horses from the same pasture. The suspected toxin damages long nerves, leading to the characteristic hyperflexion. Signs may worsen over time before stabilizing, and recovery can take weeks to months after the horse is removed from the source.

Other factors can influence how obvious the gait looks. Turning, backing, excitement, cold weather, and hard exercise may make the movement more dramatic. Because several conditions can resemble stringhalt, your vet may also consider shivers, upward fixation of the patella, lameness from foot pain, hock arthritis, and other neurologic disease during the workup.

Diagnosis usually starts with a detailed history and a hands-on exam. Your vet will watch your horse walk, turn, and back, because stringhalt is often easiest to recognize during those movements. They will also ask when the signs started, whether one or both hind limbs are involved, whether other horses on the property are affected, and what the pasture has looked like in recent weeks or months.

A key part of diagnosis is ruling out other causes of abnormal hindlimb motion. Depending on the case, your vet may perform a lameness exam, hoof testing, flexion tests, and a neurologic exam. Radiographs, ultrasound, or other diagnostics may be recommended if pain, joint disease, or a foot problem is possible. Routine bloodwork is often normal in true stringhalt, and there is no specific blood test that confirms the pasture toxin form.

In selected cases, electromyography, or EMG, may help support the diagnosis by documenting abnormal muscle and nerve activity. It is not required in every horse. In practical terms, many horses are diagnosed based on the characteristic gait pattern plus the absence of another better explanation. That distinction matters, because treatment planning depends on whether your vet believes the problem is toxin-related, chronic classical stringhalt, or a different condition that only looks similar.

Not every case can be prevented, especially classical stringhalt, because its exact cause is still unclear. Still, pasture management can lower risk for the bilateral, toxin-associated form. Horses are more likely to graze undesirable weeds when pasture is sparse, dry, or overgrazed, so maintaining forage availability matters. Regularly walk fields, identify problem weeds early, and work with your local extension service or equine veterinarian if you are unsure what is growing.

If one horse on the property develops bilateral stringhalt, review the environment quickly. Removing affected and at-risk horses from suspect pasture may help limit additional exposure. Provide clean water and safe hay or uncontaminated grazing while your vet evaluates the situation. This is especially important in late summer or drought conditions, when weed intake may increase.

Good hoof care, footing, and routine veterinary attention also help because they reduce the chance that a painful lower-limb problem will be mistaken for stringhalt or contribute to abnormal movement. If your horse develops any new hind-end gait change, early evaluation gives you the best chance to sort out whether this is a temporary look-alike problem, a pasture-related neuropathy, or a chronic movement disorder that needs longer-term planning.