Few of us think of vitamin E unless we’re also supplementing selenium, but vitamin E deficiency can cause neurological diseases, including equine degenerative myeloencephalopathy (EDM) and equine motor neuron disease (EMND). Although both diseases can be slowed, a cure is not possible.
Symptoms of EDM typically first appear around eight months of age, although it can also occur in older animals. It begins as a mild ataxia of the hind legs that then progresses to involve all four legs.
Affected horses swing their hind legs in a wide outside arc when turning. Proprioceptive deficits — the inability to tell where their legs are located — are often noted in horses with EDM. Low vitamin E levels are noted in the spinal fluid and blood of horses with EDM.
Little-to-no pasture is a risk factor. Fresh grass contains vitamin E, but hays do not, as the curing destroys vitamin E. Supplementation can help stabilize the condition, but the horse never returns to normal. Untreated horses either stabilize or reach the point they must be euthanized.
EMND strikes adult horses, with most cases noted around age 16. Symptoms are both more dramatic and more rapid in onset than with EDM.
Horses with EMND tend to have an unexplained rapid weight loss despite an excellent appetite, muscle atrophy and profound weakness. The horse may tremble when he stands and spend a lot of time lying down. When standing, he will typically hold his head low with all four legs placed farther under the body than normal. He may shift weight from one leg to the other behind.
The muscle enzymes in a horse with EMND may be elevated, and there is abnormal glucose absorption from the intestine, as with EDM. Although a definitive diagnosis requires a biopsy of the muscle that elevates the tail, the combination of symptoms and low blood vitamin E levels, with no evidence of other possible causes of similar symptoms, can be used to make the diagnosis. Lesions involve a degeneration of the nerves that control movement. The findings are strikingly similar to human amyotrophic lateral sclerosis, also know as Lou Gehrig’s disease.
As with EDM, horses without access to fresh grass are at high risk, although feeding pelleted complete feeds has also been identified as a risk factor. Oddly, a history of cribbing or manure eating is also more common in horses with EMND and may be related to the intestinal pathology. Treatment with vitamin E supplementation can arrest the disease’s progression, although a cure can’t be expected.
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