Equine Shivers: A Neuromuscular Disorder

Other Names

Shivers; shivering syndrome; equine shivering disease; stringhalt-like syndrome (incorrectly).

What is Equine Shivers?

Equine Shivers is a progressive neuromuscular disorder that affects the hindlimbs of horses, causing characteristic involuntary trembling, flexion, and abduction of one or both hind legs. The condition typically presents during specific movements — most notably when the horse is asked to back up, pick up a hindfoot, or move in tight turns. Between episodes, many affected horses appear entirely normal at the walk or trot.

Shivers is considered a distinct condition from stringhalt, though the two are sometimes confused by horse owners and less experienced practitioners. Unlike stringhalt — which causes excessive involuntary flexion during forward movement — Shivers episodes are most pronounced when the horse attempts backward motion or when a hindlimb is lifted and held.

The condition is seen across multiple breeds but appears to be over-represented in tall, heavier draught breeds including Warmbloods, Clydesdales, and Shires. It can develop at any age but is most frequently diagnosed in horses between two and eight years of age. Progression is variable — some horses remain mildly affected for years, while others deteriorate more rapidly.

Causes

The underlying cause of Equine Shivers is not fully understood, and research into the condition is ongoing. Histopathological studies of affected horses have revealed abnormalities in the cerebellum — the part of the brain responsible for coordinating smooth, controlled movement — and in the Purkinje cells that regulate cerebellar function. This suggests a degenerative process within the central nervous system rather than a primary muscle disease.

A genetic predisposition is suspected, given the familial patterns observed in certain draught breeds, but no specific causative gene has been identified. There is no evidence that the condition is caused by trauma, infection, or nutritional deficiency, though these factors may influence the rate of progression.

Interestingly, recent research has identified a possible link between Shivers and Polysaccharide Storage Myopathy (PSSM type 2 / MFM), with some horses presenting features of both conditions simultaneously.

Symptoms and Signs

The hallmark signs of Equine Shivers are triggered by specific movements and include:

Trembling, shaking, or violent flexion of a hind leg when the limb is lifted or when backing is requested
The lifted limb is held in a flexed, elevated position and trembles before being lowered
Tail is often raised or quivering simultaneously
Difficulty or resistance to moving backwards — the horse may take only one or two stumbling steps
Episodes typically resolve within seconds once the trigger movement stops
Normal gait at walk and trot between episodes in mild cases
Progressive muscle wastage over the hindquarters and croup in more advanced cases
Difficulty maintaining balance and coordination during collected work in severe cases

Farriery and veterinary examinations can be complicated in affected horses, as picking up the hindlimbs triggers episodes and makes safe handling more challenging.

Diagnosis

Diagnosis is primarily clinical, based on the characteristic episodic hindlimb trembling and flexion triggered by backing or hindlimb lifting. Your vet will observe the horse during these manoeuvres and assess the severity and frequency of episodes. A thorough neurological examination is performed to rule out other causes of hindlimb dysfunction.

Differential diagnoses to exclude include stringhalt (which affects forward movement), fibrotic myopathy (a mechanical condition causing a characteristic gait abnormality), and primary spinal cord disease. Muscle biopsy and genetic testing for overlapping myopathies (particularly PSSM) may be recommended given the emerging evidence of co-occurrence.

There are no specific blood tests that diagnose Shivers, though CK and AST may be measured to evaluate concurrent muscle disease.

Treatment

There is currently no cure for Equine Shivers and no consistently effective medical treatment. Management focuses on maintaining the horse’s quality of life, slowing progression where possible, and adapting work and handling procedures:

Dietary management — low-starch, high-fat and fibre diets and natural vitamin E supplementation (particularly if concurrent myopathy is suspected) are often trialled
Regular exercise — consistent daily turnout and low-intensity exercise may help maintain muscle condition and slow deterioration
Avoiding prolonged stabling — lack of movement appears to worsen signs in many horses
Training the horse to tolerate backing more calmly through patient, consistent handling
Adapting farriery techniques — using a hoof stand rather than holding the limb in a flexed position for extended periods can reduce stress for both horse and farrier

Muscle relaxants have been used in some cases but with inconsistent results. Physiotherapy and massage may support secondary muscle tension.

Prevention

Given the likely genetic basis of the condition, there are no reliable preventive measures. For owners of at-risk draught and warmblood breeds, maintaining optimal body condition, avoiding sudden increases in workload, and ensuring excellent overall nutrition provides the best foundation for muscle and neurological health. Horses with a family history of Shivers should be assessed before purchase if they are intended for disciplines requiring frequent backing or collection.

Prognosis

The prognosis is variable and difficult to predict in an individual horse. Some mildly affected horses remain functional and comfortable in light to moderate work for many years. Others deteriorate progressively and eventually become unsafe to handle or unable to perform their intended role. Advanced cases with significant muscle wastage and loss of coordination carry a poor long-term prognosis, and euthanasia on welfare grounds may eventually be necessary.

When to Call the Vet

Seek veterinary assessment if your horse shows hindlimb trembling or involuntary flexion when asked to back, has difficulty with hindlimb handling during farriery, or is showing progressive muscle wastage over the hindquarters. Early diagnosis helps establish a management plan before significant deterioration occurs.

Frequently Asked Questions

Is Equine Shivers the same as stringhalt?

No. Stringhalt causes involuntary, exaggerated upward flexion of the hindlimb during forward movement and is typically more obvious at the walk. Shivers primarily affects backward movement and hindlimb handling, and involves trembling and prolonged flexion rather than the abrupt snapping upward movement of stringhalt. The two can sometimes occur together, and veterinary examination is needed to distinguish them.

Can horses with Shivers still compete?

Some mildly affected horses continue to compete in disciplines that do not require frequent backing or extreme collection. However, the condition is progressive in many cases, and horses should be reassessed regularly. Disciplines involving repetitive backing, such as Western reining, are more challenging for affected horses.

Does Equine Shivers worsen in winter?

Many owners and vets report that cold weather and reduced exercise appear to exacerbate signs of Shivers. Keeping affected horses in regular work and minimising prolonged periods of box rest may help manage the condition through winter months.

Is Equine Shivers inherited?

A genetic predisposition is suspected, particularly in draught breeds, but no specific causative gene has been identified. It would be prudent not to breed from severely affected animals, though this is currently based on observed familial patterns rather than confirmed genetic testing.

For further information on equine neuromuscular disorders, the British Equine Veterinary Association (BEVA) is a reliable resource.