Vitamin E Requirements and Testing Recommendations in Horses

by Kentucky Equine Research Staff

Horses can satisfy vitamin E requirements by grazing fresh, green pasture, typically consuming about 2,000 IU per day. Modern management often limits pasture access, and while hay contains vitamin E, levels decline rapidly after baling and storage. Given these challenges, routine testing is the most reliable way to confirm your horse’s vitamin E status and prevent deficiency-related disease.

Zeroing In on Your Horse’s Vitamin E Status

“Horses should receive 1–2 IU of vitamin E (alpha-tocopherol) per kg body weight. based on a daily dry-matter intake of 2% to 2.5% of body weight. Alternatively, the total diet should supply 50 to 80 IU of vitamin E per kilogram of dry matter, an amount that provides roughly the same daily intake,” explained Catherine Whitehouse, M.S., a nutrition advisor for Kentucky Equine Research.

Vitamin E blood levels can be measured by your veterinarian. According to Carrie Finno, D.V.M., Ph.D., a board-certified internal medicine clinician at the University of California, Davis, horses should maintain blood vitamin E concentrations above 2 μg/mL.^*

Blood levels alone, though, do not necessarily indicate if signs of deficiency will develop.

“Whether or not a deficiency of vitamin E has an impact on health depends upon individual genetic factors, the temporal occurrence of deficiency during development, and the duration of deficiency,” explained Finno in her presentation at the 2024 American Association of Equine Practitioners Annual Convention.

For example, genetically susceptible foals with vitamin E deficiency may develop equine neuroaxonal dystrophy/equine degenerative myeloencephalopathy, whereas older horses with chronic vitamin E deficiency lasting more than 18 months may develop equine motor neuron disease. Other adults may develop vitamin E-responsive myopathy.

Finno recommended testing vitamin E status and supplementing horses that have levels below 2 µg/mL with vitamin E.

However, it is important to remember that different labs have different methods for analyzing vitamin E. Be sure to reference the specific range provided by the lab performing your test.

Choosing the Right Vitamin E Supplement

“Careful consideration of both product type and dose when targeting vitamin E supplementation in deficient horses is important,” she advised.

“Studies have shown that natural-source vitamin E is more effective at increasing vitamin E status in horses compared to synthetic vitamin E. Synthetic vitamin E (dl-alpha-tocopherol) contains eight different isomers, slightly different forms of the same compound that horses cannot use efficiently. Natural vitamin E (d-alpha-tocopherol) is made entirely of the isomer that horses absorb and use easily,” explained Whitehouse.

She added, “Supplementation levels above basic requirements are often needed to improve vitamin E status, making it essential that horse owners consult with their veterinarian and monitor how the individual horse responds to supplementation over time. Natural vitamin E is also available in different forms. Liquid products are water-dispersible, such as Nano-E, and have a higher bioavailability, making them the first choice when managing horses deficient in vitamin E.”

Why Follow-Up Testing Matters

Yes, routine testing of your horse’s vitamin E levels is recommended. If blood levels are still low in supplemented horses, additional testing for parasites or malabsorption may be recommended by your veterinarian.

Reprinted courtesy of Kentucky Equine Research. Kentucky Equine Research is an international equine nutrition, research, and consultation company serving horse owners and the feed industry.

Our goals are to advance the industry's knowledge of equine nutrition and exercise physiology, apply that knowledge to produce healthier, more athletic horses, and support the nutritional care of all horses throughout their lives. Learn more at Kentucky Equine Research.

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