Target Vitamin E Deficiency Early to Improve Outcomes of Horses with EMND

The prognosis for horses with equine motor neuron disease (EMND) caused by prolonged vitamin E deficiency is usually poor, but veterinarians from the University of Minnesota showed that early diagnosis and treatment can help these animals.

Equine motor neuron disease is usually diagnosed too late for the veterinarian to help the animal, said Holly E. Bedford, DVM, MS, who presented the data at the recent 2010 ACVIM (American College of Veterinary Internal Medicine) Forum held in Anaheim, Calif. Classic clinical signs of EMND include weight loss (even though the horse's appetite is normal), muscle atrophy (wasting), weakness and twitching, an elevated tail head, increased periods of recumbency (inability to stand), a camped-under stance, and occasionally black discoloration of the incisors and a pigmented retinopathy (non-inflammatory damage to the retina).

"Often, the common complaint by the owner is weight loss or decrease in performance," she said. "Often the owners interpret the muscle atrophy as weight loss."

Veterinarians base a diagnosis of EMND on finding significant muscle atrophy that affects the nervous system on a biopsy of the sacrocaudalis muscle, which is located above the tail head on either side of the spine along with low levels of vitamin E on a blood test. But Bedford said she and her colleagues would have missed 40% of their cases if they used these standard diagnostic criteria.

Instead, when the researchers examined stained frozen biopsies from horses with weakness and muscle atrophy, they noticed that mitochondrial changes and a certain type of slow-twitch muscle fiber wasting (called anguloid atrophy) were less-severe than generally expected and might signal early EMND.

"We believe that the less severe atrophy is an early sign of vitamin E deficiency, which is based on less severe clinical signs and less severe atrophy [on muscle biopsy]," she said.

They observed eight horses with clinical signs consistent with EMND. Three had acute weight loss, muscle atrophy, and weakness with low serum vitamin E concentrations. Five had a slow onset of muscle atrophy, weakness, and poor performance with low serum or low sacrocaudalis muscle tissue vitamin E concentrations.

While all eight horses had clinical signs that were consistent with EMND, none had the classic changes seen on a muscle biopsy, she said.

Only six of the eight horses had deficient vitamin E levels on serum testing. However, the two horses with normal serum levels had the same clinical signs and abnormal muscle pathology as the others, along with vitamin E deficiency in the sacrocaudalis muscles. Normal serum vitamin E concentrations may not accurately reflect the concentration of vitamin E in the muscle, Bedford warned, "therefore I would not discount vitamin E deficiency if the serum vitamin E is normal."

"Our horses received 2,000-5,000 IU/day of oral natural vitamin E supplement until serum vitamin E concentrations were within normal reference ranges (2-4 µg/ml). After serum vitamin E concentrations were normal, maintenance levels of 1,000 IU/day were recommended. Horses in training should have 4,000 IU/day due to increased demand of exercising muscle, she added.

"We believe there are early signs of vitamin E deficiency in horses. It may be slow in onset, and it may be subtle--sometimes not even recognized by the owner. But if we recognize it early and institute treatment with vitamin E, we can improve the clinical outcome of these cases," she said. She recommended owners provide access to pasture, vitamin E supplementation, and a feed with higher vitamin E levels to affected horses.

About the Author

Marie Rosenthal, MS

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