Shivers in Horses
- Horse Education Online
- 1 day ago
- 9 min read
Understanding This Progressive Neurologic Movement Disorder
Shivers is one of the most recognizable neurologic movement disorders affecting horses. Although it has been documented for well over a century, researchers are still working to fully understand why it develops. For many owners, the first indication that something is wrong occurs during routine handling. A horse that has always stood quietly for the farrier suddenly snatches a hind leg high into the air, trembles, or seems unable to place the foot back on the ground. Others first notice that their horse struggles to back up, lifting a hind leg dramatically before awkwardly setting it down.
These abnormal movements can easily be mistaken for stubbornness, poor training, fear, or even an attempt to kick. In reality, horses with shivers are not choosing these movements. They are experiencing a disorder of movement control caused by abnormalities within the nervous system.
Modern research has dramatically changed our understanding of shivers. What was once believed to be primarily a muscle disease is now recognized as a neurologic disorder involving the cerebellum, the region of the brain responsible for coordinating smooth, controlled movement.
Fortunately, many horses with mild shivers remain comfortable and useful for years with appropriate management. While there is currently no cure, understanding the condition allows owners, veterinarians, and farriers to work safely while maximizing the horse's quality of life.
What Is Shivers?
Shivers, sometimes called Shivering Syndrome, is a progressive neurologic movement disorder that primarily affects the hind limbs.
The condition is characterized by involuntary episodes of exaggerated hind limb flexion, outward movement of the leg, muscle tremors, and difficulty coordinating certain movements. These episodes are especially noticeable when the horse:
Backs up
Picks up a hind foot
Has a hind foot held by the farrier
Turns sharply
Begins moving after standing
Unlike many orthopedic problems, horses with shivers often move surprisingly normally when walking or trotting straight ahead during the early stages of the disease. This can make diagnosis challenging until the characteristic signs become obvious.
In advanced cases, abnormal movements may begin to interfere with forward locomotion as well.
Why Is It Called "Shivers"?
The name comes from the trembling or quivering that commonly occurs during an episode.
However, the condition involves much more than simple shaking. The tremors occur because the horse cannot properly coordinate muscle activity during certain movements. The visible trembling is simply one outward sign of an underlying neurologic disorder affecting movement control.
How Common Is Shivers?
Shivers is considered relatively uncommon compared with many other equine neurologic diseases.
It has been reported in numerous breeds but appears most frequently in:
Draft horses
Warmbloods
Thoroughbreds
Sport horses
Many affected horses are diagnosed during adulthood after years of apparently normal movement.
Clinical Signs of Shivers
Although every horse is different, several clinical signs are considered highly characteristic.
Difficulty Backing Up
The hallmark sign of shivers is difficulty moving backward.
Instead of taking smooth backward steps, the horse may:
Hesitate
Lift one hind limb excessively high
Swing the leg outward
Tremble while the limb is elevated
Place the foot down abruptly or awkwardly
Some horses appear almost unable to coordinate backward movement at all.
Exaggerated Hind Limb Flexion
One hind limb may suddenly flex far higher than normal.
Instead of lifting only enough to clear the ground, the horse may bring the hoof nearly to the abdomen before freezing briefly in that position.
This exaggerated flexion often lasts several seconds before the horse slowly lowers the limb.
Abduction of the Hind Limb
The affected limb often swings outward away from the body.
Veterinarians refer to this as abduction, meaning movement away from the body's midline.
This abnormal motion further distinguishes shivers from many orthopedic conditions.
Trembling
Visible trembling may occur in:
The lifted hind limb
The thigh muscles
The hindquarters
The tail
The trembling can range from subtle muscle quivering to dramatic shaking.
Problems During Farrier Work
Many horses first receive a diagnosis because of problems during hoof care.
When asked to lift a hind foot, affected horses may:
Snap the leg upward
Hold it tightly flexed
Tremble continuously
Resist having the limb extended
Struggle to return the foot to the ground
Because these movements occur suddenly, inexperienced handlers sometimes believe the horse is threatening to kick.
In reality, the horse often has little control over the movement.
For farriers, understanding this distinction is extremely important. Patience, proper positioning, and allowing the horse frequent breaks can make trimming or shoeing much safer for everyone involved.
Slow Progression
Shivers is usually progressive.
Some horses remain mildly affected for many years, while others gradually develop more severe movement abnormalities.
Eventually, abnormal movements may appear even during forward walking.
Did You Know? Many horses with shivers can walk, trot, and even perform athletic work almost normally, yet be unable to back up without obvious difficulty. This unusual combination of normal forward movement and abnormal backward movement is one of the clues veterinarians use when making a diagnosis.
What Causes Shivers?
The exact cause remains unknown.
However, research over the past decade has greatly improved our understanding of what is happening inside the nervous system.
Rather than being a disease of the muscles themselves, shivers is now believed to originate within the cerebellum, the part of the brain responsible for coordinating movement, balance, posture, and timing.
In 2015, researchers identified selective degeneration of the axons extending from Purkinje cells, specialized neurons located within the cerebellum.
Purkinje cells act like traffic controllers for movement. They help ensure muscle contractions occur smoothly and in the correct sequence. When these cells lose their normal connections, movements requiring precise coordination become abnormal.
Backing up, balancing on one hind leg, and coordinating limb placement appear to require especially complex cerebellar control, explaining why these activities are affected first.
Subsequent molecular studies published in 2023 further supported this neurologic theory by identifying abnormalities within the affected cerebellar tissue.
Is Shivers Genetic?
Researchers suspect genetics may contribute to the condition, particularly in certain breeds.
However, no single gene has been identified, and the exact inheritance pattern remains unknown.
Because of this uncertainty, veterinarians cannot currently predict which horses will eventually develop shivers.
Is Shivers the Same as Stringhalt?
No.
Although both disorders involve abnormal hind limb movement, they are very different conditions.
Shivers | |
Most obvious when backing or lifting a hind foot | Most obvious during forward walking |
Hind limb held in exaggerated flexion | Sudden upward snapping motion of the leg |
Often accompanied by trembling | Usually no prolonged trembling |
Thought to involve cerebellar dysfunction | Mechanism differs and may involve peripheral nerves |
If you would like to learn more, read our article on Stringhalt in Horses, where we discuss this disorder in detail and explain how veterinarians distinguish it from shivers.
Could It Be Another Neurologic Disease?
Several neurologic disorders can affect the hind limbs.
These include:
Unlike these disorders, horses with shivers often maintain normal strength and awareness while displaying very specific abnormalities during backing and limb handling.
If you would like to learn more about these conditions, explore our articles on EPM, West Nile Virus, Wobbler Syndrome, Ataxia, and Sidewinder Syndrome, where we discuss their causes, diagnosis, and prognosis.
Use our Neuro Screen & Localization Assistant to see how different symptoms correlate with different conditions.
Did You Know? For many years, shivers was thought to be a muscle disease because affected horses often show enlarged or overactive hindquarter muscles. Modern research has shown that the primary problem lies within the nervous system, not the muscles themselves.
Is Shivers Painful?
Current evidence suggests shivers is not primarily a painful condition.
Instead, it represents abnormal movement caused by impaired neurologic coordination.
However, affected horses can become:
Frustrated
Anxious
Resistant during handling
Repeated struggling during hoof care or backing exercises may also lead to secondary muscle soreness or fatigue.
Because the horse cannot voluntarily control these movements, punishment or forceful correction should never be used.
How Is Shivers Diagnosed?
There is no blood test, genetic test, or single imaging study that confirms shivers.
Diagnosis relies primarily on clinical examination.
Veterinarians typically observe:
The horse walking forward
The horse backing up
Each hind limb being lifted individually
Tail movement
Muscle tone
Coordination
Additional testing may be performed to rule out:
Muscle disease
Other neurologic disorders
Researchers have also investigated three-dimensional motion analysis as a way to objectively measure the abnormal movements, although this technology is currently used mainly in research settings.
Treatment and Management
There is currently no cure for shivers.
Treatment focuses on maintaining function while minimizing stress and injury.
Management strategies include:
Maintain Regular Exercise
Many horses appear to perform better when kept in consistent work.
Regular movement may reduce the frequency or severity of episodes.
Reduce Stall Confinement
Extended stall rest may worsen clinical signs in some horses.
Whenever medically appropriate, regular turnout is often recommended.
Modify Farrier Handling
Because hoof care is commonly affected, farriers often adapt their techniques.
Helpful strategies include:
Picking up the foot slowly
Supporting the limb comfortably
Avoiding prolonged flexion
Taking frequent breaks
Allowing the horse time to regain balance
Avoid Punishment
The horse is not being disobedient.
Attempting to force normal movement through punishment only increases stress and may worsen handling difficulties.
Regular Veterinary Monitoring
Periodic examinations allow veterinarians to monitor disease progression while ruling out additional neurologic disorders that may develop.
Prognosis
The long-term outlook varies considerably.
Some horses remain only mildly affected throughout their lives.
Others gradually develop increasing difficulty with:
Hoof care
Backing
Athletic performance
General coordination
Many horses continue living comfortable lives as pleasure horses, while those requiring advanced athletic precision may eventually become limited.
Did You Know? Some horses with shivers compete successfully in lower-level disciplines for years after diagnosis. Disease progression is often slow, and many horses remain comfortable with appropriate management and patient handling.
Living With a Horse That Has Shivers
Owners can make life considerably easier by understanding the disorder.
Helpful practices include:
Keep handling calm and predictable.
Allow extra time during hoof care.
Avoid forcing backward movement.
Work closely with your veterinarian and farrier.
Monitor changes over time.
Recognize that worsening signs should prompt reevaluation.
Educating everyone who handles the horse is equally important. Riders, barn staff, and farriers should understand that the abnormal movements are involuntary rather than behavioral.
Current Research
Although tremendous progress has been made, many questions remain unanswered.
Researchers continue investigating:
Why Purkinje cell degeneration develops
Possible genetic influences
Biomarkers for earlier diagnosis
Better methods for measuring disease progression
Potential future therapies targeting cerebellar function
As our understanding of equine neurology continues to grow, future treatments may become possible.
Learn to Recognize Lameness and Gait Faults
Shivers is one of many gait abnormalities that can affect a horse's movement. Being able to recognize the difference between gait faults caused by neurological disease, lameness, or conformational problems is an important skill for every horse owner and equine professional. To help you build that knowledge, Horse Education Online offers a downloadable Lameness Flashcard Study Set and a downloadable Gait Fault Flashcard Study Set. These printable flashcards illustrate and explain common lamenesses and gait abnormalities, making it easy to study at home, prepare for certifications, or sharpen your observational skills in the barn. You may also enroll in our Online Equine Lameness Certification Program for an even more in-depth dive.
Key Takeaway
Shivers is a progressive neurologic movement disorder that primarily affects the coordination of the hind limbs during backing and limb handling. Although the condition can appear dramatic, it is not simply poor behavior, bad training, or ordinary lameness.
Modern research has shown that abnormalities within the cerebellum play a central role in the disease, helping explain why horses struggle with precise movements such as backing up or holding a hind foot for the farrier. While there is currently no cure, many horses remain comfortable and useful for years with thoughtful management, regular exercise, skilled farrier care, and ongoing veterinary monitoring.
Frequently Asked Questions
1. What is the first sign of shivers in horses?
The earliest sign is usually difficulty backing up or exaggerated lifting of one hind leg when it is picked up for hoof care.
2. Is shivers a form of lameness?
No. Shivers is a neurologic movement disorder rather than an orthopedic lameness.
3. Can horses with shivers still be ridden?
Many horses with mild shivers can continue riding and light athletic work, although advanced cases may become limited.
4. Is shivers painful?
Current evidence suggests the condition itself is not primarily painful, although secondary muscle soreness or stress may develop.
5. Can shivers be cured?
There is currently no proven cure. Management focuses on maintaining mobility and reducing stress.
6. How is shivers diagnosed?
Diagnosis is based on clinical examination, observation of the horse backing and lifting its hind limbs, and ruling out other neurologic or orthopedic diseases.
7. Is shivers hereditary?
A genetic component is suspected, but no definitive inheritance pattern has been established.
8. How is shivers different from stringhalt?
Stringhalt is most noticeable during forward walking, whereas shivers is most apparent during backing and when a hind foot is lifted.
9. What should a farrier know about horses with shivers?
The horse's abnormal leg movements are involuntary. Slow handling, patience, and frequent breaks often make trimming or shoeing safer and less stressful.
10. Does shivers always get worse?
Not necessarily. Some horses remain mildly affected for many years, while others experience gradual progression. Regular veterinary evaluations help monitor changes over time.
References
Aman, J. E., Valberg, S. J., Michalski, K. J., Bender, J. B., & Johnston, C. (2018). Abnormal locomotor muscle recruitment activity is present in horses with Shivering and Purkinje cell distal axonopathy. Equine Veterinary Journal.
Seino, K. K. S., DeClue, A. E., Foreman, J. H., et al. (2019). Three-dimensional kinematic motion analysis of Shivers in horses: A pilot study. Journal of Equine Veterinary Science.
Valberg, S. J., Lewis, S. S., Shivers, J. L., Barnes, N. E., Konczak, J., Draper, A. C. E., & Armien, A. G. (2015). The equine movement disorder "Shivers" is associated with selective cerebellar Purkinje cell axonal degeneration. Veterinary Pathology.
Valentine, B. A., et al. (1999). Clinical and pathologic findings in two draft horses with progressive muscle atrophy, neuromuscular weakness, and abnormal gait characteristic of shivers syndrome. Journal of the American Veterinary Medical Association.
Williams, Z. J., Finno, C. J., Henry, M. L., et al. (2023). Cerebellar axonopathy in Shivers horses identified by spatial transcriptomic and proteomic analyses. Journal of Veterinary Internal Medicine.
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