Cover Story | Lameness

Managing Vitamin E Deficiency in Today’s Horse

By Marie Rosenthal MS

One reason there are fewer horses today suffering with neuromuscular disease is because veterinarians better understand the importance of vitamin E in the horse’s diet, according to Sarah F. Colmer, VMD, DACVIM-LAIM, an internal medicine specialist and neurology fellow at the University of Pennsylvania School of Veterinary Medicine, in Philadelphia.

Vitamin E is an important antioxidant that’s imperative for neuromuscular health. Fresh green grass is the primary dietary staple for horses to get vitamin E, and stored feed may have less. In addition, the animal’s metabolism may vary the amount of vitamin E the horse gets.

“Veterinarians must consider the individual animal even in a uniformly managed herd,” Dr. Colmer said, “because there may be varying metabolism [individually] in some of the horses or malabsorption that might affect individual vitamin E levels.”

For many horses that do get an acquired neurodegenerative disease, their history often shows limited access to pasture for long periods, she said. Clinical signs include significant muscle wasting, weight loss, fasciculations, excessive recumbency and weight shifting. And sometimes their stance looks like an “elephant [balancing] on a ball.”

Evaluation for equine motor neuron disease (MND) should include a biopsy of the sacrocaudalis dorsalis medialis (SCDM)—otherwise known as the tail head muscle. The typical histopathologic findings for the SCDM biopsy include moth-eaten fibers and very angular muscle fibers, Dr. Colmer explained.

“Treatment involves high doses of vitamin E supplementation, and prognosis can be quite variable,” she said. “About 45% of these cases seem to respond to high-dose vitamin E therapy,” she said, adding that in about 69% of cases, including some who were treated, euthanasia will be required within 3 months.

“And some horses can stabilize, but they may not necessarily show improvement,” she warned.

In more recent years, clinicians and researchers identified a subset of horses with clinical signs that indicate a more subtle form of neuron disease, consistent with vitamin E-responsive myopathy (VEM), she said. There is some muscle atrophy and weakness, and possibly low serum vitamin E concentrations, although this is not the case in all of these subtle cases, and the owner or trainer often complains of poor performance with the horse.

“Importantly, the thing that defines this group of horses is that many of them may improve with vitamin E supplementation before they reach that MND ‘point of no return’,” she said.

At PennVet’s New Bolton Center, Dr. Colmer said, equine neuroaxonal dystrophy (eNAD) and equine degenerative myeloencephalopathy (EDM) are the leading causes of neurologic disease they see. They are often chronic symmetric mild-to-moderate ataxia conditions that may include behavioral changes.

Unfortunately, there is no available diagnostic test in the living horse for these conditions (eNAD/EDM). In a case series at New Bolton, 73 of 100 horses with eNAD or EDM had ataxia, and 69% of those had an element of abnormal behavior, she said.

“Horses with eNAD or EDM probably have a multifactorial etiology for these diseases,” she added. “We know that many of these horses have low levels of vitamin E, but not all.” There may be genetic predispositions, environmental exposures to different substances like wood preservatives and pesticides as well as a nutritional component at play, according to Dr. Colmer.

“Sometimes supplementation may help some of these horses with aspects of their clinical signs, but it may not necessarily cure these horses,” she said.

Regarding testing for vitamin E levels: “It’s very important that you pay attention to different laboratories that use different methodologies and have different reference ranges [for vitamin E],” she said.

“For our laboratory, the reference range is technically 2 to 10 mcg/mL, but we tend to try to keep our horses that have neurologic or muscular concerns closer to the middle of that reference range,” she said.

When adding supplementation, “not all products are created equally, but it is important to have a quality product when you are supplementing these horses. Products come in different formulations, such as powders, pellets and liquids,” she added.

For very deficient animals, she often recommends starting at 5,000 IUs per average size horse per day, and rechecking the horse’s levels after 1 or 2 months of supplementation.

Although vitamin E appears safe for supplementation, there is still the thought that there can be too much a good thing. Some researchers have identified possible complications including association with vitamin K antagonism and bleeding. “So, it behooves you to consider testing for vitamin E,” she said. MeV