vitamin e supplements
Vitamin E is an essential nutrient in the equine diet, meaning horses cannot make it themselves and must consume it through their diets. Horses can easily meet this requirement with adequate access to high-quality pasture. However, vitamin E levels drop rapidly in preserved forages (think hay). And horses with decreased vitamin E levels can be at risk for developing some neuromuscular conditions. As such, owners might need to supplement this vitamin in their horses’ diets, one veterinarian and researcher said.

Carrie Finno, DVM, PhD, Dipl. ACVIM, assistant professor at the University of California, Davis, School of Veterinary Medicine, has studied vitamin E and its effects on equine neuromuscular conditions extensively. She shared her recommendations for effective vitamin E supplementation at the 2018 American Association of Equine Practitioners Convention, held Dec. 1-5 in San Francisco, California.

Why Is Vitamin E Important?

Vitamin E is a collective term used to describe a group of eight compounds known as tocopherols, the most bioavailable of which is alpha-tocopherol (α-TOH)—in particular, RRR stereoisomer (RRR-α-TOH).  Once absorbed, this form is the most bioactive in animal tissue because the liver takes it up preferentially.

Vitamin E is a fat-soluble vitamin that plays a critical role in neuromuscular health. The National Research Council recommends horses consume 1-2 IU of vitamin E per kilogram of body weight per day, which equals 1,000-2,000 IU per day for a 500-kilogram (1,100-pound) horse.  Veterinarians typically use serum levels of α-TOH to assess a horse’s whole-body vitamin E status, with values of >2 µg/mL considered to be normal. Individual metabolism of vitamin E between horses varies greatly, Finno stressed.

Horses with with a vitamin E deficiency can be at risk for several conditions, including equine motor neuron disease (EMND), vitamin E deficient myopathy (VEM), equine neuroaxonal dystrophy/equine degenerative myeloencephalopathy (eNAD/EDM), as well as general muscle soreness and poor performance. Whether a vitamin-E-deficient horse will develop these conditions depends on multiple factors, such as the extent of the deficiency, genetic predisposition, and when during the horse’s life the deficiency occurs.

Finno’s research has shown that foals with eNAD/EDM have very low α-TOH levels in their cerebrospinal fluid, suggesting that if vitamin E deficiencies occur in genetically susceptible foals during their first year of life, eNAD/EDM might result.

In adult horses, length of deficiency might be a key factor in what health conditions occur. A short-term deficiency might result in muscle weakness, while longer-term deficiencies might lead to full-blown VEM. In her work with Stephanie Valberg, DVM, PhD, Dipl. ACVIM, ACVSMR, of Michigan State University, Finno has shown that apparently healthy horses had serum α-TOH below 2 µg/ml. Even more worrying, she said, they showed abnormal mitochondria in approximately 4% of their muscle fibers.

Supplementing Vitamin E

Finno recommended all horses on less than 12 hours per day of good-quality pasture receive supplemental vitamin E and that all horses should have their serum α-TOH levels monitored. Research has shown that the most rapid rises in serum α-TOH concentrations occur when horses consume water-soluble liquid forms of α-TOH at 10 IU/kg body weight per day, said Finno. In fact, serum levels more than double in 12 hours with 5,000 IU, and cerebrospinal fluid levels of α-TOH increase significantly after 14 days when supplemented with 5,000 IU of the water-dispersible product.

Natural-source liquid forms of , so when their horses need long-term supplementation, owners are often keen to use more cost-effective powdered forms instead. Finno cautioned that switching from the natural liquid α-TOH to a powdered α-TOH acetate form can result in a significant decrease in serum α-TOH unless owners make the transition gradually. She recommended avoiding synthetic α-TOH altogether, as it does not effectively increase serum α-TOH.

Based on her work, Finno shared the following protocols for supplementing α-TOH-deficient horses:

  • If deficient (serum α-TOH <2 µg/mL) with no clinical signs of neuromuscular disease, supplement with 2,500 IU/450 kg body weight per day of liquid natural α-TOH;
  • If deficient and showing symptoms of neuromuscular disease, supplement with 5,000 IU/450 kg body weight per day of liquid natural α-TOH.
  • Horses with normal α-TOH do not need supplementation but should be rechecked at six-month intervals or after diet changes.

Recheck supplemented horses’ α-TOH levels after three weeks, said Finno. If they are within normal ranges, you can add natural α-TOH acetate powder or pellets to the diet at 5,000 IU per day and reduce the liquid natural α-TOH gradually over a 12-week period. At that point, recheck serum levels, she said. If these are normal, you can reduce α-TOH acetate to 3,000 IU per 450 kilograms (roughly 1,000 pounds) of body weight per day and recheck the horse in six months. Should the horse turn up deficient after the 12-week transition, he’ll need to go back on the liquid and maintained on the lowest dose possible to remain >2 µg/mL serum α-TOH.

For horses that are deficient after three weeks on 2,500 IU/450 kilogram body weight per day of liquid α-TOH, increase their dose to 5,000 IU. If normal after three weeks at this level of supplementation, you can transition to the powdered/pelleted α-TOH acetate. Otherwise, increase the dose to 7,500 IU/450 kilogram body weight per day for three weeks before transitioning to α-TOH acetate if serum levels are then normal.

Finno said her research has identified that some horses fail to respond to even the highest levels of supplementation with the liquid natural α-TOH form. She believes these horses might have malabsorption due to parasite damage or gastrointestinal inflammation.

She cautioned against supplementing at levels greater than 10,000 IU per day or 20 IU/kilogram body weight of the natural α-TOH acetate powder or pellet. This is the National Research Council’s upper safe limit, based upon the synthetic product; levels beyond this might lead to coagulopathy (reduced ability for the blood to coagulate) and impaired bone mineralization. Finno only recommends doses higher than 5,000 IU/day of the liquid α-TOH if veterinarians have confirmed horses have not responded to that dose.

Serum values exceeding 5 µg/mL are too high, and doses need to be reduced. Finno pointed out that, in humans, more than 50% of cytochrome isoforms that metabolize therapeutic drugs also metabolize vitamin E. This means that particularly large doses of vitamin E might impact the efficacy of some therapeutic drugs also being given to the horse.

Take-Home Message

With horses having less access to quality pasture—whether due to obesity concerns, lack of available space, or their performance management—vitamin E supplementation and monitoring should be an essential part of equine management. With routine blood work and a strategic supplementation protocol, it is possible to avoid the negative consequences associated with vitamin E deficiency.