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Equine Vitamin E Deficiency

Equine Journal

December Ask the Vet

Author: Taryn Gervais, D.V.M., of New England Equine Medical and Surgical Center |

Date Added: November 30, 2011 |

Q: How can you tell if your horse is deficient in vitamin E? How will it affect your horse? What can you do to combat it?

A:  A horse’s vitamin E level can be determined by measuring the vitamin E content of serum or plasma samples that are obtained from the blood. A deficiency of vitamin E can manifest as nutritional myodegeneration (a.k.a. white muscle disease), in either the cardiac form or the skeletal form. Nutritional myodegeneration is related to a deficiency of either vitamin E or selenium. Vitamin E deficiency can also manifest in Equine Motor Neuron Disease, which is a product of chronic (long-standing) vitamin E deficiency.

The cardiac form of nutritional myodegeneration is marked by severe myocardial (heart muscle) decompensation, and is often seen in fast-growing animals, with lesions in the heart, diaphragm and intercostals muscles. This form usually has a sudden onset and results in a fast decline with death, despite medical therapy. The skeletal form of nutritional myodegeneration usually has a slower onset, with clinical signs of muscle weakness and stiffness. Affected animals have muscle weakness, trembling, and may even be unable to stand or ambulate. They will commonly have hardened, swollen muscle groups. Clinical signs of the skeletal form of nutritional myodegeneration can also include difficulty eating (due to weakness of the tongue muscles), difficulty breathing (due to weakness of the diaphragmatic and intercostals muscles), and signs of cardiac dysfunction (due to cardiomyopathy). Animals with the skeletal form of nutritional myodegeneration often respond well to medical treatment, which will include the administration of both vitamin E and also selenium.

The more common effect of vitamin E deficiency seen in adult horses is Equine Motor Neuron Disease. There are two forms of EMND described, the subacute and the chronic forms. The subacute form is manifested as acute onset of trembling, muscle fasciculations, frequent recumbency (lying down), hind limb weight shifting, low head carriage, loss of muscle mass, and possibly a strong appetite. The chronic form of EMND is manifested as improved trembling and muscle fasciculations, which may subside altogether, and muscle atrophy, as well as a high tail/head position. The lack of vitamin E in EMND horses causes lesions to form in the lower motor neurons of the spinal cord gray matter, as well as various cranial nerves and other parts of the neurologic network essential for normal function. These parts of the nervous system undergo noninflammatory degeneration, and the muscles that are innervated by these affected neurons undergo neurogenic atrophy, meaning that they become weak and lose mass because of lack of neurologic input. When about 30% of motor neurons are affected, clinical signs develop.

Equine Motor Neuron Disease can affect all breeds and is usually seen affecting only a single animal in a barn rather than as a herd outbreak. Horses with EMND usually have had no pasture access for over a year before their clinical signs begin to present. Diets deficient in green foodstuffs (i.e. pasture), with poor quality grass hay and no access to alfalfa or supplemenation of vitamin E can predispose a horse to EMND. Aside from measuring a horse’s plasma vitamin E level, a veterinarian can also test for EMND with a more invasive test, which involves submitting a sample of the sacrocaudalis dorsalis muscle for analysis.

Treatment for Equine Motor Neuron Disease involves supplementation of the diet with oral vitamin E (5000-7000 IU per day). This can improve horses that are clinically affected with EMND, but it is unlikely to produce full resolution of signs, due to the inability to restore dead neurons.

As a means of preventing these consequences of vitamin E deficiency, owners can provide all horses that lack access to good quality grass or green hay for over a year with oral vitamin E supplementation at the level previously described. Additionally, these horses should have their plasma vitamin E levels monitored routinely.

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