Shivers in horses is a condition that leaves many owners searching for answers. 

A horse that suddenly struggles to move smoothly, legs trembling with no clear cause, can be a troubling sight. 

What’s behind these unusual spasms? How does it impact a horse’s daily life? 

In this guide, we’ll uncover what Shivers is, the signs to watch for, and what can be done to manage it. 

Let’s explore the mystery of Shivers and what it means for horses and their care.

What is Shivers in Horses?

Shivers is a neurological condition seen in horses, primarily affecting the hind limbs. 

It causes involuntary muscle spasms, making the horse’s leg tremble or jerk, especially when the horse backs up or lifts a hind leg. 

Scientists believe it may stem from an issue in the central nervous system, though the exact cause remains unknown.

The condition is more common in large breeds, such as draft horses and warmbloods, and may have a genetic link. 

In affected horses, the muscles around the hind legs don’t function properly, leading to noticeable spasms or “shivering” movements. 

Over time, Shivers can worsen, making simple tasks difficult for the horse, like standing for farrier work.

Classification of Equine Shivers

Shivers in horses is usually classified based on the types and direction of leg movement affected.

Here’s a breakdown of these classifications:

Hyperflexion

Hyperflexion involves excessive bending of the joints, particularly in the hind legs. 

When a horse with Shivers tries to lift its leg, it often bends the hock and stiffle joints more than normal, pulling the leg up high toward the belly. 

This movement is involuntary and can happen suddenly.

Forward hyperflexion

Forward hyperflexion is a variation where the horse’s leg bends at a steep angle but moves slightly forward, rather than straight up. 

It’s like the leg is lifting toward the horse’s chest instead of just under the belly. 

This type of flexion often occurs when the horse tries to back up or turn, making these movements uncomfortable and difficult.

Hyperextension

Hyperextension is the opposite of hyperflexion. Instead of bending excessively, the joints extend or stretch beyond their normal range. 

In horses with Shivers, this may happen as the leg extends backward, giving a “stiff” or “locked” appearance. 

Hyperextension can make simple standing or walking challenging, as the leg becomes rigid and hard to move normally.

Risk Factors of Equine Shivers

The risk factors for Shivers in horses include:

1. Breed predisposition

Certain breeds, especially large or heavy ones, are more prone to Shivers. 

Draft breeds, warmbloods, and some sport horses like dressage and eventing horses show a higher incidence. 

2. Genetic factors

While Shivers isn’t fully understood, there appears to be a genetic component. 

Horses with family histories of Shivers are more likely to develop the condition.

3. Body size and muscle mass

Larger horses with significant muscle mass, especially in the hindquarters, are at greater risk. 

The higher body mass may strain the nervous system, making these horses more susceptible to neuromuscular disorders like Shivers.

4. Diet and nutritional imbalance

Diets low in essential nutrients or lacking specific electrolytes can aggravate Shivers. 

High-carbohydrate diets and low-fat diets may contribute to symptom development or severity, though this area needs more research.

5. Performance and workload

Horses with high workloads, especially in disciplines requiring hind-leg engagement, may be more prone to developing Shivers or showing worsened symptoms. 

Intensive training may increase muscle stress, contributing to the risk.

6. Age

Shivers often become more noticeable as horses mature, typically emerging around five years or older. 

As horses age, symptoms may progress, making age an important risk factor.

Causes of Equine Shivers

The exact cause of Shivers in horses is not fully understood. 

However, research suggests several potential factors that may contribute to its development. 

Here are the key causes:

1. Neurological dysfunction

Shivers is a neurological disorder, originating in the brain, specifically in the cerebellum, which coordinates muscle movement. 

Damage or abnormal function in this area may cause the tremors and spasms typical of Shivers.

2. Genetic predisposition

There seems to be a genetic component to Shivers, especially since it is more common in specific breeds.

Horses with a family history of Shivers may be more likely to develop the condition, suggesting a hereditary influence.

3. Abnormal muscle function

In horses with Shivers, the muscles around the hind limbs don’t contract and relax in a normal pattern. 

This abnormality may be due to disrupted nerve signals or imbalanced neurotransmitters, which help nerves communicate. 

When these signals are disrupted, the muscles can contract or release involuntarily, causing the trembling and spasms seen in Shivers. 

4. Nutritional imbalances

Imbalances in nutrients, such as low-fat and high-carbohydrate diets, may exacerbate Shivers symptoms. 

Horses with a deficiency in essential vitamins or minerals (e.g., magnesium or vitamin E) might have an increased risk.

5. High body mass and muscle bulk

Larger horses with significant muscle mass, especially in the hindquarters, may be at a higher risk of developing Shivers. 

The increased weight and muscle bulk might strain the nervous system, leading to neuromuscular issues.

6. Overexertion or high workload

Horses used in high-performance disciplines, such as dressage or eventing, may be at higher risk. 

The stress from heavy workloads could trigger or worsen Shivers symptoms in susceptible horses.

Signs of Shivers in Horses

Shivers in horses present with a range of symptoms, from mild to severe. 

These signs are primarily observed in the hind limbs and worsen as the condition progresses.

Mild clinical signs

Mild tremors. Slight quivering or trembling of the hind legs, especially noticeable when the horse lifts a leg.

Occasional leg lifting. The horse may lift a hind leg abnormally high, even without moving.

Stiffness in movement. Some horses may show mild stiffness when backing up or making turns.

Difficulty holding feet up for farrier. Horses may struggle slightly during farrier work, lifting the leg but with minor control issues.

Head and tail movements. Mild, involuntary head shaking or tail twitching can sometimes accompany early stages of Shivers.

Severe clinical signs

Pronounced muscle spasms. Strong spasms that cause the hind leg to jerk upwards involuntarily, often held in the air before slowly lowering it.

Frequent and intense leg lifting. The horse may repeatedly lift one or both hind legs, especially when asked to move backward or when stressed.

Severe stiffness and locking. Significant rigidity in the hindquarters, making movement difficult or almost impossible in severe cases.

Reluctance or inability to back up. Horses with advanced Shivers may refuse to back up or do so with extreme difficulty.

Loss of balance and coordination. In severe cases, the horse may lose balance, struggle to stay steady, or show poor coordination during movement.

How to Diagnose Shivers in Equines

Diagnosing Shivers in horses involves careful steps to identify symptoms and rule out similar conditions. 

Here’s a breakdown of each step:

1. Physical and behavioral observation

The first step is watching how the horse moves. A vet will observe the horse as it backs up, turns, or lifts a hind leg. 

Horses with Shivers often show leg trembling, stiffness, or exaggerated lifting. 

These behaviors help reveal early signs of Shivers.

2. Neurological examination

A neurological exam helps the vet check how well the horse’s nervous system is working. 

This exam includes testing muscle tone, reflexes, and sensitivity. 

By examining these areas, the vet can see if there are issues with how the muscles and nerves work together, which often shows up as trembling or spasms.

3. Differential diagnosis

Shivers can look like other conditions, such as Stringhalt or EPM. 

To diagnose Shivers accurately, the vet must rule out these other possibilities. 

This may involve blood tests, X-rays, or other exams to ensure the symptoms aren’t caused by another condition.

4. Medical history and breed assessment

The vet will also look at the horse’s medical history and breed. 

Shivers is more common in certain breeds, like draft horses and warmbloods. 

Information about the horse’s age, workload, and family history of Shivers can give important clues in making a diagnosis.

5. Advanced diagnostic tools

Sometimes, the vet may use advanced tools like electromyography (EMG) to study muscle activity. 

EMG can show abnormal muscle contractions, which help confirm Shivers. 

Imaging, like MRI or CT scans, can also be helpful if there are complex cases or other suspected conditions.

How to Treat Shivers in Horses

Treating Shivers in horses focuses on managing symptoms since there is currently no cure. 

Some essential strategies for treating and managing shivers are:

1. Dietary adjustments

Adjusting the horse’s diet can help manage symptoms. 

A high-fat, low-carbohydrate diet is best, as it may reduce muscle spasms and improve muscle control. 

Adding fat sources like rice bran or vegetable oil can also provide energy without triggering excessive carbohydrate intake. 

2. Regular, low-impact exercise

Exercise that strengthens muscles without straining the horse’s hindquarters is beneficial. 

Regular, low-impact activities like walking or light trotting can help maintain muscle tone and flexibility. 

Consistent exercise also prevents stiffness, which may ease some symptoms. 

3. Farrier modifications and hoof care

Shivers can make hoof care challenging, so you need to work with an experienced farrier. 

Farriers may use modifications like extra support or shoeing techniques to help the horse stand comfortably during trimming or shoeing. 

Shorter, more frequent farrier sessions can also help minimize stress.

4. Muscle relaxants and supplements

Some horses may benefit from muscle relaxants prescribed by a vet to reduce spasms. 

Additionally, supplements like magnesium and vitamin E may support muscle and nerve function. 

Always consult a vet before introducing any medication or supplement, as not all horses will react the same way.

5. Consistent routine and stress reduction

Horses with Shivers often respond well to a calm and predictable environment. 

Minimize stress, establish a consistent daily routine, and avoid sudden changes in their schedules to help reduce symptom flare-ups. 

6. Physical therapy and stretching

Some horses benefit from physical therapy, stretching, and chiropractic care. 

Work with a certified equine therapist to provide targeted exercises that support the horse’s muscle health.

Prevention of Shivers

Preventing Shivers in horses can be challenging since the exact cause is still unknown. 

However, certain practices may help reduce the risk, especially for horses predisposed to the condition. 

Here are some preventive steps:

Selective breeding. Avoid breeding horses with a family history of Shivers to reduce genetic risk.

Balanced nutrition. Provide a high-fat, low-carbohydrate diet to support muscle and nerve health.

Consistent, low-impact exercise. Keep up regular, gentle exercise to maintain muscle tone without overstraining.

Avoid overworking young horses. Introduce training gradually to prevent muscle and nervous system strain.

Routine health monitoring. Schedule regular veterinary check-ups to catch early signs and adjust care as needed.

What is the Prognosis of Shivers?

The prognosis for Shivers in horses is generally cautious. 

Shivers is a progressive condition with no cure, and symptoms often worsen over time. 

However, some horses experience only mild symptoms that remain stable with good management. 

Studies show that around 60-70% of horses with Shivers can lead functional lives if managed carefully. 

About 30-40% of horses may see symptoms progress, affecting tasks like backing up or standing for hoof work. 

Severe cases may lead to balance issues and impact the horse’s quality of life.

In sports like jumping or dressage, where hind-leg engagement is critical, up to 50% of affected horses may need to retire early. 

Early diagnosis and consistent care can improve a horse’s comfort and help control symptoms. 

Potential Rule Out for Shivers

When diagnosing Shivers, a vet needs to rule out similar conditions that may cause confusion. The conditions are:

1. Stringhalt

This causes the horse’s hind leg to lift suddenly and high, usually due to nerve damage.

Unlike Shivers, Stringhalt appears more during movement than in stationary positions.

2. Upward fixation of the patella

In this condition, the knee cap locks, causing the leg to stay extended or “catch.” 

This differs from Shivers, where trembling and spasms are the main signs.

3. Fibrotic myopathy

This causes a restricted, short stride due to scarring in the muscles, usually in one leg. 

It doesn’t produce the tremors or “shivering” effect seen in Shivers.

4. Stiff-Horse Syndrome (SHS)

A rare condition, SHS causes a constant stiff-legged gait due to muscle rigidity. 

It can look like Shivers, but SHS creates constant stiffness, while Shivers symptoms are more episodic.

5. Equine Motor Neuron Disease (EMND)

EMND causes muscle wasting and weakness rather than the spasms seen in Shivers. 

Horses with EMND often lose muscle mass, which is uncommon in Shivers cases.

6. Equine Protozoal Myeloencephalitis (EPM)

EPM affects the nervous system, leading to muscle weakness and balance issues across the body. 

Shivers, by contrast, primarily affects the hind limbs with specific tremors.

FAQs

Conclusion

Shivers in horses can be a challenging condition, but understanding it is the first step to helping your horse live comfortably. 

While there’s no cure, proper management can make a huge difference. 

With the right diet, gentle exercise, and attentive care, many horses with Shivers lead fulfilling lives. 

Remember, early detection and a steady routine are key. Work closely with your vet to ensure the best support for your horse. 

Shivers may be a mystery, but with knowledge and patience, you can help your horse navigate it more easily.