Shivers

Shivers is a poorly understood progressive neurological condition characterized by involuntary muscle tremoring and abnormal movement patterns in the hind legs, usually becoming more pronounced when the horse is asked to back up or when the hind legs are lifted. The condition ranges from barely noticeable fine tremoring to severe, dramatic muscle shaking that significantly impacts the horse's movement and athletic ability. Unlike seizures or other neurological conditions, shivers doesn't cause loss of consciousness or sudden collapse—instead, the horse maintains awareness and control while experiencing involuntary muscle contractions that interfere with coordinated movement.

Why understanding shivers matters is that it's a progressive condition that tends to worsen over time, particularly with continued athletic work. Early recognition allows you to make management decisions that slow progression and maintain quality of life longer. Conversely, continuing athletic work as shivers worsens can accelerate decline. Understanding what you're dealing with helps you make informed decisions about your horse's future.

The exact cause of shivers remains unclear. Research suggests it might involve dysfunction in the spinal cord or neuromuscular junction, but definitive cause hasn't been established. Shivers appears to have some genetic component and is more common in some breeds (particularly Warmbloods and draft horses) than others. The condition cannot be cured, though management can sometimes help maintain function.

Shivers is one of the few conditions where a veterinary diagnosis is primarily based on clinical presentation rather than laboratory findings. There's no blood test or imaging study that definitively diagnoses shivers. Your veterinarian diagnoses based on the characteristic tremoring patterns, how the condition presents, and ruling out other causes of abnormal hind leg movement.

This guide will explain what shivers is, what causes or contributes to its development, what signs you'll observe, how veterinarians approach diagnosis, and most importantly, how to manage a horse with shivers to maximize comfort and quality of life while the condition progresses.

The underlying cause of shivers remains unknown despite decades of research. This is one of the frustrating realities of managing the condition—there's no identified root cause to address, making prevention impossible and cure impossible. The condition appears to involve dysfunction in the nervous system's control of hind limb muscles, but the precise mechanism is unclear.

Genetic predisposition appears to play a significant role. Shivers runs in some families and breeds, suggesting hereditary factors contribute. Warmbloods and draft horse breeds show higher incidence than other breeds. Some horses appear to be born with a predisposition that manifests as the horse matures. This genetic component means that shivers horses should not be bred, as offspring have increased risk of inheriting the condition.

Spinal cord involvement is suspected by some researchers. The tremoring pattern and movement abnormalities suggest possible dysfunction in the spinal cord's control of hind limb muscles. However, necropsy studies have not consistently shown structural abnormalities that would explain the clinical signs.

Neuromuscular junction dysfunction is another hypothesis. If the communication between nerves and muscles is disrupted, it could produce the involuntary tremoring observed in shivers. However, this mechanism remains speculative.

Exercise intensity sometimes appears to influence shivers manifestation. Horses exercised heavily might show more prominent signs than those with light activity. This observation has led to the theory that excessive neuromuscular activation triggers or exacerbates the condition. However, this isn't universally true—some shivers horses show signs regardless of activity level.

Stress or excitement sometimes exacerbates shivers signs. A horse that shows mild shivers at rest might show much more pronounced signs when nervous or excited. This suggests that emotional state or neuromuscular activation somehow influences the expression of the condition.

Progression timing is somewhat variable. Some horses show signs early in life (young adults), while others don't manifest obvious shivers until their teens or later. The reason for this variation in timing isn't understood. Some horses' conditions progress rapidly, while others progress slowly over years.

Fine muscle tremoring in the hind legs is the hallest characteristic sign of shivers. This tremoring is involuntary and particularly pronounced when the horse is asked to back up. When backing, the hind legs might show obvious shaking or tremoring that makes the movement jerky and uncoordinated. The tremoring might be subtle at first—just a slight shakiness—or might be dramatic and obvious.

Abnormal hind limb movement is characteristic. When walking or trotting, a shivers-affected horse might move stiffly in the hind legs, perhaps with slight goose-stepping movements. The movement appears uncoordinated or lacking fluid quality. Someschlorses show exaggerated movement with dramatic knee action in front and stiff, jerky movement behind.

Difficulty picking up the hind legs is common. When a farrier tries to pick a hind leg to trim the hoof, a horse with shivers might have difficulty lifting and holding the leg steady. The leg might shake, and the horse might have difficulty maintaining balance on three legs. This difficulty persists even for experienced horses that have been having their feet trimmed without issue.

Shaking when hind legs are lifted is highly characteristic. Gently lifting a hind leg upward often produces pronounced tremoring. This tremoring might be visible as obvious muscle shaking or might just be a vibration you can feel in the leg. This sign is often used diagnostically because it's quite characteristic of shivers and occurs reliably in affected horses.

Squatting or straddling of the hind legs sometimes occurs. A shivers horse might position their hind legs in a wide stance or unusual positions, perhaps to compensate for the difficulty with coordinated movement. Some horses have difficulty achieving a normal stance.

Difficulty in backing up is characteristic. Backing movement requires coordinated control of hind legs, and shivers horses often struggle with this. They might back jerkily, crookedly, or with tremoring that makes the movement difficult. Some severely affected horses become almost unable to back at all.

Progressive worsening over time is typical. A horse showing very mild signs might progress to more pronounced signs over months or years. The rate of progression varies, but shivers is generally a progressive condition. What starts as barely noticeable tremoring when backing might develop into obvious movement abnormalities at all times.

Signs that worsen with exercise sometimes occur. Some horses show more pronounced shivers signs when fatigued or after heavy work. The tremoring might be barely noticeable at the beginning of a ride but much more obvious at the end.

Emotional influence on signs is common. A nervous, excited, or anxious horse might show much more pronounced shivers signs than a calm one. This temporal relationship between emotional state and shivers manifestation is important for management.

Signs that might mimic or be confused with other conditions sometimes create diagnostic confusion. A young horse with early shivers might be mistaken for a horse with poor training or bad attitudes because the movement abnormalities might appear behaviorally motivated. Careful examination and understanding of the condition helps avoid misdiagnosis.

Diagnosis of shivers is primarily clinical, based on the characteristic signs observed during physical examination and movement evaluation. Your veterinarian will examine your horse's movement, assess hind limb coordination and control, and observe how the horse responds when the hind legs are lifted or when backing is requested. The characteristic tremoring when hind legs are lifted is particularly diagnostic.

Lameness evaluation helps rule out orthopedic causes of abnormal hind limb movement. Your vet will assess for lameness, joint problems, or other orthopedic issues that might mimic shivers. Shivers horses are typically not lame, though severely affected horses might move so abnormally that lameness becomes difficult to assess.

Radiography might be recommended to rule out skeletal or spinal problems that could cause similar signs. X-rays of the hocks and other hind limb joints can rule out arthritis or other joint disease. Radiographs of the spine are sometimes taken to rule out spinal compression or other structural problems.

Equine neurological examination is performed to assess the horse's neurological status overall. The veterinarian evaluates reflexes, cranial nerve function, movement, and other neurological parameters. Shivers horses typically have normal neurological examination findings aside from the abnormal hind limb signs.

There is no blood test or imaging study that definitively diagnoses shivers. The diagnosis is made based on the clinical presentation and the characteristic signs. This is one of the diagnostic challenges—there's no confirmatory test, so diagnosis relies on recognizing the pattern of signs.

Unfortunately, there is no cure for shivers. The condition is progressive and cannot be reversed. Treatment focuses on managing signs, maintaining comfort, and helping the horse live as normally as possible despite the condition.

Muscle relaxants and anti-inflammatory medications sometimes help manage shivers signs, though the evidence for effectiveness is limited. Phenylbutazone might provide some pain relief or reduction of inflammation. Dantrolene, a muscle relaxant, has shown some promise in managing shivers, though results are inconsistent and the medication can have side effects.

Vitamin E supplementation is sometimes recommended, as deficiency has been theoretically linked to some neuromuscular conditions. While there's no strong evidence that supplementing vitamin E helps shivers specifically, some horses might benefit.

Herbal and alternative treatments are used by many owners, though evidence for efficacy is largely anecdotal. Some horses seem to improve somewhat with various supplements or therapies, though it's often unclear whether the improvement reflects natural variation in the condition or actual treatment benefit.

Management and activity modification are the primary approaches to helping a shivers horse. Accepting that the condition is progressive and will worsen over time helps inform management decisions.

Managing a shivers horse involves accepting the progressive nature of the condition while implementing strategies that maintain quality of life as long as possible. Activity level should be adjusted based on the severity of the condition and the horse's comfort level. A horse with very mild shivers might continue light ridden work, while a more severely affected horse might need to be retired from riding.

Exercise should be light and consistent rather than intense and sporadic. A shivers horse benefits from daily light activity—hand-walking, light pasture turnout, gentle ridden work—more than from sporadic intense work that might exacerbate the condition. Consistent light exercise might slow progression compared to inactivity.

Avoiding backing under saddle is often recommended for shivers horses, as backing exacerbates the condition and is often difficult for affected horses. This limits the activities the horse can participate in but reduces stress on the compromised neurological system.

Trimming and farrier care requires special consideration. A farrier accustomed to working with shivers horses can often manage hoof care despite the tremoring and difficulty with hind leg manipulation. Communication with your farrier about the condition helps them understand what they're dealing with and work safely and effectively.

Feeding and nutrition should be optimized. A horse in good condition and receiving quality nutrition is better able to tolerate the progressive decline. Ensuring adequate minerals, vitamins, and protein supports overall health.

Mental stimulation and companionship remain important despite the horse's physical limitations. Many shivers horses benefit from interaction with their handlers and other horses, provided the activity level matches their physical capabilities.

Monitoring progression helps you recognize when the horse's condition is worsening and management adjustments are needed. Regular evaluation of how the horse is moving and functioning allows you to adapt management accordingly.

Emotional management of the condition is important for owners. Accepting that shivers is progressive and the horse will eventually need retirement helps owners make appropriate long-term plans rather than struggling through progressive decline. Some owners find it helpful to retire the horse to pasture earlier rather than pushing them to continue work as the condition worsens.

Prevention of shivers is largely impossible given the genetic predisposition and unknown underlying cause. Shivers horses should not be bred, as offspring have increased risk of inheriting the condition. If you own a horse with shivers, neutering or spaying (if female) prevents breeding of affected animals.

No specific management or environmental factors have been proven to prevent shivers from developing in genetically predisposed horses. Maintaining good overall health doesn't prevent the condition, though it might help the horse tolerate it better.

Prognosis for shivers is guarded to poor. The condition is progressive and will eventually worsen to the point where the horse can no longer be ridden or perform athletic work. The timeline for progression varies tremendously. Some horses have barely detectable shivers and progress slowly over years. Others show significant signs and progress rapidly, potentially becoming unable to perform within months or a few years.

Life expectancy in shivers horses is generally normal—the condition doesn't directly threaten life. However, at some point, the horse will become so affected that riding and athletic work are no longer feasible. At that stage, some horses can live contentedly in pasture or with light activity. Others struggle with the dramatic movement abnormalities and diminished quality of life.

Quality of life assessment is crucial when managing shivers progression. A horse that can walk comfortably, has normal social interactions with other horses, and appears content has reasonable quality of life despite the condition. A horse struggling with movement, appearing distressed, or unable to perform any of the activities they previously enjoyed might be approaching the point where euthanasia is a humane option.

Retirement to pasture is often the eventual outcome for shivers horses. As the condition progresses and ridden work becomes impossible, many shivers horses do well with pasture living and light interaction with handlers. They can often live years in this state if quality of life is maintained.

The decision about when a shivers horse should be euthanized is deeply personal and depends on the horse's individual condition, the owner's resources, and the horse's quality of life. Regular discussions with your veterinarian help you monitor the horse's condition and make informed decisions about the horse's long-term future.