Vitamin E is produced by living plants exposed to the sun (1). It is a powerful antioxidant with key functions in immune health, reproduction, regulating the normal response to inflammation and muscular function (2). Fresh grass contains the highest amount of vitamin E, with a loss of approximately 50% within the first month of storage (3).
This is important to remember when considering whether your horse may be suffering from a condition related to a deficiency of vitamin E. If your horse does not have access to fresh grass, they may not be receiving an adequate amount of vitamin E. This might, however, not only be an issue during the winter months, when days are short, horses are on decreased turn out and grass does not grow as much due to the lack of sun. It may also be a consideration when a horse is on a prolonged period of box rest, with limited periods of hand grazing.
How much vitamin E does my horse need?
This value depends on your horse’s activity level. A 500kg horse needs (2):
Adult (no exercise, including stallions, breeding and pregnant mares) - 500 IU/ day.
Adult (light exercise) - 800 IU/ day.
Adult (moderate exercise) - 900 IU/ day.
Adult (heavy exercise) - 1000 IU/ day.
A horse with a vitamin E deficiency may need a higher amount.
What are the common signs of horses with a vitamin E deficiency?
Not every horse with a vitamin E deficiency will have clinical signs of disease. Affected horses may:
Display signs of poor performance.
Struggle to build up strength and topline.
Fatigue quickly.
Take a longer time to recover from exercise.
Long term vitamin E deficiency can also lead to Equine Motor Neuron Disease and Equine Degenerative Myeloencephalopathy (2).
How can I find out if my horse has a vitamin E deficiency?
A blood test is readily available through your regular vet practice. Your vet can then discuss these results with you, and make an appropriate plan going forward. It is important to note that sometimes, horses with normal blood serum vitamin E levels still do not have adequate levels of vitamin E within their muscles, and therefore require supplementation anyway.
Which supplement should you pick?
There are 2 types of supplements - synthetic and natural.
The natural form is more bioavailable, meaning that it is more easily absorbed and therefore more effective (4). Although a lot of balancers contain some vitamin E, it is usually inadequate and mainly in the synthetic form.
Side effects from high-dose supplementation in horses is thought to be low risk (2), however, giving the proposed recommended dose (above) would be advocated unless your horse is actually showing symptoms of vitamin E deficiency or has decreased serum levels.
Some vitamin E supplements are produced in combination with another antioxidant - Selenium. Although vitamin E is fairly safe even at high levels, this is not the case with selenium and extra caution should be taken.
Conclusion
Even though a vitamin E deficiency is more likely to be the case during the winter months due to lack of fresh grass, it should be considered as a possible cause of poor performance, especially in horses struggling to build topline.
References
Fritsche, S., Wang, X. and Jung, C. (2017) “Recent advances in our understanding of tocopherol biosynthesis in plants: An overview of key genes, functions, and breeding of vitamin E improved crops,” Antioxidants, 6(4), p. 99.
Finno, C.J. and Valberg, S.J. (2012) “A comparative review of vitamin E and associated equine disorders,” Journal of Veterinary Internal Medicine, 26(6), pp. 1251–1266.
McDowell LR. Vitamin E. In: LR McDowell, ed. Vitamins in Animal Nutrition. San Diego, CA: Academic Press, Inc; 1989: 93– 131.
Fiorellino, N. M., Lamprecht, E. D. & Williams, C. A. (2009) Absorption of Different Oral Formulations of Natural Vitamin E in Horses. Journal of Equine Veterinary Science, 29(2): 100-104.