Equine motor neuron disease is a disease which affects the motor neurons in the spinal cord and brain stem of horses. Cases have been documented in the United States and worldwide. While the exact cause of equine motor neuron disease isn’t known, researchers have correlated a vitamin deficiency with the likelihood of horses developing the disease.
Fortunately, the chances of a horse getting equine motor neuron disease can be greatly reduced by diet or vitamin supplementation. While there is not a treatment option which guarantees success, diagnosing the disease and starting treatment early gives the horse the greatest chance of recovery.
What Is Equine Motor Neuron Disease?
Motor neurons are responsible for sending signals to the muscles in a horse, causing them to contract and allowing the horse to move. Equine motor neuron disease affects the motor neurons, eventually causing damage to them if untreated. It is thought that damage to the motor neurons occurs by oxidative stress caused by free radicals. The disease was first identified by researchers in 1990, typically affecting older horses with a median age of 10. Researchers found that the feeding and housing of horses seemed to be the primary cause of the disease, as opposed to the genetics of certain horse breeds.
The early symptoms of the disease are muscle weakness and loss. As the disease develops, horses may have difficulty standing and may frequently shift their weight on their hind legs or lay down more than normal. Other symptoms include an uncoordinated gait, muscle trembling or spasms, weight, and muscle loss despite the horse eating a normal amount of food, or the horse not lifting its head.
What Causes Equine Motor Neuron Disease?
In 1990, researchers identified equine motor neuron disease and found that it was most common in horses which did not have access to pastures for grazing and were fed grain instead. This led researchers to investigate vitamin deficiencies in horses with the disease. Horses that were affected by the equine motor neuron disease were found to have lower plasma levels of vitamin E. In a study conducted in 2007, 10 out of 11 horses fed a low vitamin E diet developed the disease within 44 months.
Treatment Options Available for Equine Motor Disease
While a vitamin E deficiency may be linked to the development of equine motor neuron disease, the exact cause of the disease remains unknown. The prognosis once a horse has been diagnosed with equine motor neuron disease varies, so the best option is to prevent the disease before it develops. However, once a horse starts exhibiting symptoms of equine motor neuron disease, the current treatment is supplementation of the horse’s diet with vitamin E. Vitamin E is an antioxidant that can neutralize free radicals, preventing or reversing damage to the motor neurons.
In all cases studied by researchers, horses with the equine motor neuron disease are deficient in vitamin E. Plasma vitamin E levels can be determined by a blood test. Veterinarians will sometimes also perform a muscle biopsy to determine if the horse’s symptoms are being caused by other illnesses. Once a horse has been diagnosed with equine motor neuron disease, horses are given supplements of at least 5000 IU of vitamin E.
A horse’s prognosis after beginning vitamin E supplementation varies. In some cases, horses make a full recovery. In others, symptoms may disappear, but the horse may relapse in the future if put back to work. Sometimes, the progression of the disease is halted but the horse never returns to normal. Other times, the supplementation may have no effect at all and the disease progresses. Since the disease is still not well understood, a horse’s recovery varies case-by-case. Diagnosing the disease early and beginning a regiment of supplementation is currently the only treatment option.
Prevention of Equine Motor Neuron Disease
Since the treatment options for the equine motor neuron disease are limited, the best option is to prevent it from developing. Allowing horses to graze in pastures supplies them with sufficient vitamin E to help prevent the disease. For horse owners that are concerned about their feed or soil, tests can be ordered by a veterinarian to determine if the levels in the feed or soil are sufficient for a horse’s diet.
Pasture grazing may not always be an option, for example, if there are seasonal or available land limitations. In these cases, horses are typically fed a grain-based diet. To help prevent equine motor neuron disease, horses should be given regular vitamin E supplements. Vitamin E supplements derived from natural sources are typically better absorbed by the horse than synthetic vitamin E. Vitamin E supplements should be labeled d-alpha tocopherol, the form of vitamin E which is present in natural sources.
Again, since the cause of the disease is not completely understood, there is no guarantee that diet or supplementation will completely prevent the disease. However, ensuring that a horse receives adequate vitamin E may help prevent its appearance.
Equine motor neuron disease is a disease that affects the motor neurons of a horse, affecting the horse’s muscles and its ability to stand and walk. The leading risk factor for the disease is thought to be a vitamin E deficiency, caused by the horse’s diet. To help prevent the disease, a horse should be allowed to graze in pastures if possible. If pasture grazing isn’t possible, the horse’s diet should be supplemented with naturally derived vitamin E. Once symptoms appear, supplementation with vitamin E is currently the only treatment option, and the effectiveness varies case-by-case.
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