Shivers in Horses: Causes, Symptoms, Diagnosis, and Management

Shivers is a neurological disorder in horses that affects coordination and control of the hind limbs, particularly during movements such as backing up or lifting the hind legs. Horses with shivers display characteristic trembling, spasms, or abnormal limb positioning, most often when asked to pick up a hind foot or move backwards.

The condition can range from mild to severe and is most commonly observed in large breeds such as warmbloods, draught horses, and draft crosses. Although shivers has been recognised for more than a century, the exact cause remains unclear. Understanding how the condition presents and progresses can help horse owners manage affected horses effectively.

What Is Shivers

Shivers is a chronic neuromuscular disorder that interferes with the horse’s ability to control certain movements of the hind limbs and tail. It is considered a neurological condition, affecting the signals between the brain, spinal cord, and muscles responsible for coordinated movement.

The disorder typically becomes noticeable when a horse is asked to lift a hind leg, back up, or hold a hind limb flexed, such as during hoof trimming or shoeing. Instead of lifting the limb smoothly, the horse may show sudden trembling, jerking movements, or prolonged spasms.

In many cases, horses appear completely normal when walking or trotting forward, particularly in the early stages of the condition.

Breeds Commonly Affected

Although shivers can occur in any horse, certain breeds appear to be more predisposed.

Breeds frequently affected include:

• Warmbloods
• Draught horses
• Draft crosses
• Thoroughbreds
• Sport horses

The condition is most often diagnosed in young to middle-aged horses, though symptoms may develop gradually over time.

Causes of Shivers

The exact cause of shivers is not fully understood, but research suggests it involves abnormalities in the nervous system, particularly areas of the brain responsible for coordination and motor control.

Recent studies have linked shivers to dysfunction in the cerebellum, the region of the brain that regulates balance and movement precision.

Possible Contributing Factors

Several factors may play a role in the development of shivers:

• Degeneration of nerve cells controlling muscle coordination
• Abnormal muscle metabolism
• Genetic predisposition
• Underlying neuromuscular disorders
• Associated muscle diseases such as polysaccharide storage myopathy (PSSM) in some horses

While trauma or injury is rarely the cause, the condition may become more noticeable during periods of increased workload or stress.

Symptoms of Shivers

The signs of shivers vary in severity but typically involve abnormal hind limb movement, especially when the horse is asked to lift or hold a hind leg.

Common Clinical Signs

• Sudden trembling of the hind limb when lifted
• Difficulty holding the hind leg up for hoof picking or shoeing
• Jerking or spasmodic movements of the limb
• Tail elevation or trembling during episodes
• Difficulty backing up
• Abnormal hind limb posture when attempting to move backwards

Some horses may lift the hind limb very high and hold it in a flexed position while the muscles tremble.

Behaviour During Farrier Work

Shivers is often first noticed by a farrier because the horse struggles to hold a hind foot up. When the limb is lifted:

• The leg may suddenly jerk upward
• Muscles may tremble or shake
• The horse may snatch the leg away
• The tail may elevate or quiver

These episodes can last several seconds before the limb returns to normal.

Advanced Cases

In more severe or advanced cases, additional signs may develop:

• Difficulty backing up
• Abnormal hind limb movement when turning
• Increased frequency of muscle spasms
• Progressive coordination problems

Despite these abnormalities, many horses remain capable of forward movement and exercise.

Diagnosis

Diagnosing shivers is usually based on clinical observation of characteristic movements, as there is currently no single laboratory test that confirms the condition.

Veterinary Examination

A veterinarian will assess the horse’s gait and neurological function by observing:

• Walking and trotting in a straight line
• Turning in tight circles
• Backing up
• Picking up and holding the hind limbs

The difficulty backing up combined with tremors during hind limb flexion is often strongly suggestive of shivers.

Diagnostic Tests

Although diagnosis is primarily clinical, additional testing may be used to rule out other conditions.

Possible tests include:

• Blood tests to assess muscle enzymes
• Genetic testing for muscle disorders such as PSSM
• Neurological examination
• Muscle biopsy in some cases

These tests help distinguish shivers from other neuromuscular disorders.

Conditions That Can Be Confused With Shivers

Several conditions can cause abnormal hind limb movement similar to shivers.

Differential Diagnoses

• Stringhalt
• Fibrotic myopathy
• Upward fixation of the patella
• Equine motor neurone disease
• Other neurological disorders affecting coordination

A veterinary examination is important to ensure an accurate diagnosis.

Treatment

Currently, there is no cure for shivers, but many horses can be managed successfully with appropriate care.

Treatment focuses on improving muscle function, reducing symptoms, and maintaining the horse’s comfort and mobility.

Exercise Management

Regular exercise is often beneficial for horses with shivers.

Recommended management includes:

• Consistent turnout
• Regular light to moderate exercise
• Avoiding prolonged stall confinement
• Maintaining overall fitness

Many horses move more comfortably once warmed up and in regular work.

Nutritional Management

Dietary adjustments may help support muscle and nerve function.

Common nutritional strategies include:

• Diets low in starch and sugar
• Increased dietary fat for energy
• Vitamin E supplementation
• Balanced mineral intake

In horses with concurrent PSSM, specialised diets may be required.

Farrier Management

Because shivers often affects the horse’s ability to hold a hind leg up, farrier work may require special handling techniques.

Helpful strategies include:

• Allowing frequent breaks during trimming or shoeing
• Supporting the limb in a lower position
• Avoiding excessive limb flexion
• Using patient, calm handling

Experienced farriers often develop techniques to manage affected horses safely.

Prognosis

The progression of shivers varies between horses.

Mild Cases

• Horses may remain stable for many years
• Performance may not be significantly affected
• Regular exercise often helps manage symptoms

Progressive Cases

• Coordination issues may gradually worsen
• Backing up may become increasingly difficult
• Some horses eventually develop more obvious gait abnormalities

Despite this, many horses with shivers continue to live comfortable lives with appropriate management.

Prevention

Because the underlying cause of shivers is not fully understood, specific prevention strategies are limited.

However, good general management may help reduce the severity of symptoms.

Management Recommendations

• Maintain consistent exercise routines
• Provide balanced nutrition
• Monitor horses for early neurological signs
• Seek veterinary advice if abnormal hind limb movement develops

Early recognition allows owners to adapt management strategies before the condition becomes more challenging.

When to Contact a Veterinarian

Horse owners should consult a veterinarian if they notice:

• Trembling of the hind limbs when lifted
• Difficulty holding a hind foot for cleaning or shoeing
• Trouble backing up
• Unusual tail movements during limb flexion
• Progressive coordination problems

Early veterinary assessment can help confirm the diagnosis and rule out other treatable conditions.

Conclusion

Shivers is a chronic neurological condition that affects hind limb coordination in horses, particularly during movements such as backing up or lifting the hind legs. While the exact cause remains uncertain, the disorder is thought to involve abnormalities in the brain regions responsible for motor control.

Although there is no cure, many horses with shivers can be managed successfully through regular exercise, appropriate nutrition, and patient handling during hoof care. With proper management and veterinary guidance, affected horses can often continue to work and maintain a good quality of life.