Bit & Bridle

Equine Stringhalt

Other Names

  • Equine Reflex Hypertonia
  • Acquired Stringhalt
  • Australian Stringhalt
  • Classic Stringhalt

What Is Stringhalt in Horses?

Stringhalt is a neuromuscular condition characterised by an involuntary, exaggerated upward flexion of one or both hindlimbs. Affected horses exhibit a distinctive jerky, snapping movement in which one or both hind legs are snatched sharply upward towards the abdomen during the forward phase of each stride. The severity ranges from a subtle flick that may only be noticeable at certain gaits or in specific conditions, through to a dramatic, violent involuntary movement that makes normal locomotion nearly impossible.

The condition arises from dysfunction in the neural pathways controlling hindlimb movement — specifically an abnormality in the reflex arc involving the lateral digital extensor muscle. When this reflex behaves abnormally, the result is uncontrolled, hyperexaggerated limb elevation rather than the smooth, coordinated movement of a healthy horse.

Stringhalt is classified into two broad forms. Classic (or “true”) stringhalt typically affects one hindlimb and is usually associated with specific local causes. Australian (or acquired) stringhalt affects one or both limbs simultaneously and is associated with pasture toxicity — most commonly ingestion of hypochoeris radicata (flatweed/false dandelion) or other toxic plants. Understanding which form is present influences both treatment and prognosis significantly.

Causes

The causes of stringhalt differ between the two main forms:

Classic (Unilateral) Stringhalt

  • Trauma to the dorsal pastern or fetlock: Injury to the dorsal aspect of the lower limb — lacerations, adhesions, or scar tissue over the fetlock or pastern — can tether or interfere with the normal action of the lateral digital extensor tendon, producing an abnormal reflex response.
  • Joint or soft tissue adhesions: Adhesions from old injuries or surgery around the hock or fetlock can disrupt normal limb mechanics.
  • Idiopathic: In many cases of unilateral stringhalt, no specific underlying cause can be identified despite thorough investigation.

Australian (Bilateral) Stringhalt

  • Plant toxicity: Associated with ingestion of hypochoeris radicata (flatweed), a plant that proliferates in overgrazed, stressed, or drought-affected pastures. Other implicated plants include dandelion and mallow in various outbreaks.
  • Distal axonopathy: The toxin(s) in these plants are thought to cause damage to the longest peripheral motor and sensory nerves — a “dying-back” neuropathy affecting the distal axons.
  • Pasture conditions: Outbreaks typically occur when pastures are stressed — following drought, poor grazing management, or overgrazing — which increases flatweed abundance relative to desirable grasses.

Symptoms and Signs

The hallmark sign is unmistakable once seen:

  • Involuntary hindlimb elevation: Sudden, involuntary snatching of one or both hind feet sharply upward during the forward phase of the stride. In mild cases, the limb is elevated slightly above normal; in severe cases, it is snapped up towards the belly with considerable force.
  • Worse at certain times: Signs are often exacerbated when the horse is cold, turning in a tight circle, backing, or first starting to move after standing still. Some horses show minimal signs once warmed up at active gaits.
  • Bilateral involvement: Australian stringhalt typically affects both hindlimbs, which can result in a characteristic “bunny hopping” or severely disrupted gait. Horses in severe bilateral cases may have great difficulty walking.
  • Muscle wasting: In prolonged or severe cases, atrophy of the hindquarter muscles — particularly the distal limb muscles — may become apparent.
  • Associated with other neurological signs in severe cases: In severe Australian stringhalt outbreaks, affected horses may also show weakness, dysphagia (difficulty swallowing), and weight loss reflecting more widespread neuropathy.

Diagnosis

Diagnosis is based primarily on clinical observation of the characteristic gait abnormality. Additional steps include:

  • Gait assessment: Observation at walk, trot, backing, and turning. Asking the horse to back several steps is a reliable way to exacerbate signs in mildly affected horses.
  • History and pasture evaluation: In cases of bilateral stringhalt, a thorough pasture history, including recent drought or overgrazing, and an assessment of the pasture for flatweed or other toxic plants is essential.
  • Rectal examination and neurological assessment: A full neurological examination helps characterise the extent of neural involvement and rule out spinal cord disease that could mimic aspects of stringhalt.
  • Lower limb radiography and ultrasonography: Relevant in cases where trauma or adhesions to the fetlock or pastern region are suspected as a cause of classic unilateral stringhalt.
  • Electromyography (EMG): Nerve conduction studies and muscle electromyography can document the extent of peripheral nerve dysfunction in cases of Australian stringhalt, supporting the diagnosis and potentially informing prognosis.

Treatment

Treatment depends on the form and severity:

Australian (Pasture-Associated) Stringhalt

  • Pasture removal: The most important step is removing the horse from the affected pasture immediately. In many cases, clinical signs improve spontaneously over weeks to months once the source of toxin is eliminated. Mild to moderate cases often recover fully with pasture removal alone.
  • Supplementary feeding: Provide good-quality hay and a balanced diet to support recovery and reduce reliance on the affected pasture.
  • Phenytoin: The anticonvulsant phenytoin has been used in some cases to reduce the severity of involuntary limb movements and provide temporary relief during recovery, though its use requires veterinary supervision and is not universally effective.

Classic (Unilateral) Stringhalt

  • Lateral digital extensor tenectomy: Surgical removal of a section of the lateral digital extensor tendon (myotenectomy) is the primary treatment for classic unilateral stringhalt and is frequently effective in reducing or eliminating signs. The procedure involves excision of a portion of the tendon under general or standing sedation, depending on the approach used.
  • Addressing underlying causes: Adhesions, scar tissue, or injuries to the dorsal pastern or fetlock should be addressed surgically if present.

The BEVA advises veterinary diagnosis before considering surgical intervention, as not all horses with apparent stringhalt are surgical candidates. For related hindlimb conditions, see our article on Equine Bone Spavin.

Prevention

  • Monitor pastures regularly for flatweed (hypochoeris radicata) — a common low-growing weed with yellow dandelion-like flowers. It flourishes on overgrazed, stressed, or drought-affected pastures.
  • Maintain healthy pasture through appropriate stocking rates, fertilisation, and reseeding after drought — this reduces the proportion of weeds relative to desirable species.
  • Avoid turning horses onto severely overgrazed paddocks where weeds dominate the available grazing.
  • Where flatweed is present, apply herbicide or mechanically remove it before allowing horse access.
  • Manage all lower limb injuries promptly and carefully to reduce the risk of adhesions developing around the fetlock and pastern.

Prognosis

Prognosis depends on the form and severity of stringhalt:

For Australian (pasture-associated) stringhalt, the prognosis with early pasture removal is generally good. Mild to moderate cases often recover fully within three to twelve months. Severe cases may have permanent residual gait abnormalities. Horses that remain on affected pasture continue to deteriorate and may not recover fully even after removal.

For classic unilateral stringhalt, lateral digital extensor tenectomy offers meaningful improvement in many cases, though not all horses return to completely normal gait. Mild residual signs may persist in some horses post-surgery. Horses with a clearly identified underlying cause that has been successfully treated have the best outcomes.

When to Call the Vet

Contact your vet if you observe:

  • Any involuntary, exaggerated upward snapping of one or both hindlimbs during movement
  • Multiple horses in the same paddock developing similar gait abnormalities simultaneously — a cluster of cases suggests Australian stringhalt and warrants immediate pasture investigation
  • Progressive worsening of gait abnormality in a horse on pasture
  • Muscle wasting of the hindquarters alongside altered gait
  • Any horse that is struggling to walk normally due to hindlimb movement abnormality

Frequently Asked Questions

Is stringhalt painful for horses?

Classic stringhalt is generally not believed to be painful — it is a neurological reflex abnormality rather than a primary pain response. However, severe bilateral cases can be distressing for the horse due to the loss of controlled movement, and the physical violence of the limb snapping can cause secondary injuries. Horses with severe stringhalt may show distress and exhaustion from the constant involuntary movement.

Can a horse with stringhalt be ridden?

This depends entirely on severity. Horses with mild unilateral stringhalt may continue in work with minimal impact on performance. Horses with severe bilateral stringhalt may be unsafe to ride and unable to perform normal gaits. After successful surgical treatment or pasture removal and recovery, return to ridden work is often possible. Each case must be assessed individually by your vet in the context of the intended use.

How common is flatweed in UK pastures?

Hypochoeris radicata (flatweed or cat’s ear) is found throughout the UK and is a common component of established pastures, lawns, and rough ground. However, Australian stringhalt outbreaks are more commonly reported in Australia and parts of North America than in the UK, possibly due to differences in the specific toxin concentrations in different geographic populations of the plant. UK horse owners should nonetheless monitor pastures for weed dominance and manage accordingly.

Will stringhalt come back after surgery?

Recurrence after lateral digital extensor tenectomy is possible but not the norm in cases where the surgery is performed correctly. Some horses show partial improvement rather than complete resolution of signs. Horses whose stringhalt is due to a pasture toxin and who return to the contaminated pasture will relapse — the surgery does not address the neurological root cause in Australian stringhalt cases and is not the appropriate primary treatment for that form.