What are Shivers?
As noted above, shivers in horses has a long equine history and has, over the centuries, been described as being relatively common or uncommon and rare or very rare. Shivers, according to more recent data, seems to begin to show up in horses who are aged 5 years or older and, a recent study revealed that about 74 percent of those horses having shivers were progressing in the degree of severity of this disorder involving hind limb movement.
Shivers, or shivering, has a long equine history. Gait abnormality when backing up is the main characterization of this gradually progressive, chronic neuromuscular disease.
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Symptoms of Shivers in Horses
The symptoms of shivers in horses are similar to those seen in other neuromuscular conditions like stringhalt, stiff-horse syndrome and equine motor neuron disease (EMND). Though these symptoms are similar, the root cause is not. These symptoms can be occasional, intermittent and latent, making the early signs of this disease difficult to see. Here are some symptoms you might note to some degree in a horse with shivers:
- Involuntary muscle spasms or movements in the pelvis, one or both hind limbs or tail (movements are jerky - for example, a horse might jerk a hind limb away when it is picked up for cleaning or for shoeing)
- Most apparent when horse is asked to back up - the hind leg may raise abruptly, remain in a flexed position slightly away from the horse’s body and be held there for a duration lasting from seconds to several minutes
- After putting limb down, horse may experience more spasms especially if asked to move backward
- Involuntary muscle movements can be worse in slippery conditions, or when the horse is excited or under stress
- Though most often affects hind limbs, involuntary movements rarely can affect front limbs, head and trunk and occasionally ears, eyelids, lips and cheeks
Shivers in horses usually displays symptoms between the ages of 5 and 10 years and can affect both male and female genders of any breed. It generally affects males more often than females, with geldings being reported to have three times higher risk of development. This disease also seems to be more prevalent in taller horses than those which are shorter, with those horses that are 16.3 hands tall being the most often afflicted. There are two types or categories of shivers in horses:
- Hyperflexion - One hind limb is raised and held away from the horse’s body and the raised limb quivers while raised up; the limb is returned quickly to the ground when the spasms cease and can occur in one or both hind limbs
- Hyperextension - When moving backwards, the afflicted horse will place both hind limbs farther back than normal and will also place the front limbs farther forward than normal, giving a saw horse look to his stance
Causes of Shivers in Horses
There is no known cause for shivers in horses, though much research has been done to find one. Some feel the condition is a genetic one or that it at least has some genetic components but this has not been proven. No lesions have been found in any part of the neurological system in any horse. Research is ongoing and some researchers have isolated the portion of the brain which seems to affect the shivers and locomotion but as yet have not been able to take the research beyond that point.
Diagnosis of Shivers in Horses
A thorough physical examination will be required by your veterinary professional. He must rule out other possible conditions, some of which are more painful. Blood testing usually doesn’t show any abnormalities and the muscle enzymes like CK and AST are usually within normal range. Your vet will need to rule out other conditions like stringhalt, fibrotic myopathy, stiff-horse syndrome (SHS), equine motor neuron disease (EMND) and equine protozoal myeloencephalitis (EPM) as these diseases have similar symptoms and signs.
In regard to possible genetic involvement, there is, at this time, no genetic pattern specific to this disease and there is no test available to isolate it. Diagnosis will likely occur when the symptoms are indicative of shivers and other diseases and conditions with similar signs and symptoms have been ruled out.
Treatment of Shivers in Horses
As noted above, there has been no cause determined for shivers in horses. Without a cause, a cure is not possible. Treatment of the symptoms is pretty much all that can be offered. Some vets might suggest changing the horse’s diet to one which includes high fat and low carbohydrates but this has not been proven to effectively manage the disease. Rest is the best treatment to calm the symptoms but, be aware, the symptoms will likely return when exercise and other stressors are resumed.
Recovery of Shivers in Horses
There is no known cause for shivers in horses and, accordingly, there can be no cure until a cause is determined. For the horse afflicted with shivers, it can be expected that the condition will progressively worsen with eventual debilitation of the horse in its future. Sometimes the symptoms will calm down with rest but then return when the horse resumes exercise.
The prognosis can be poor for the horse diagnosed with shivers and the best you can do for him is love him and keep him as comfortable as possible. There will be good days and there will be bad days for your horse. As the disease advances, there will be increased frequency and severity of the symptoms, muscle wasting, and weakness. It can progress quickly or may take as long as 24 years to cause a horse to reach a point of incapacitation.