In your quest to find the most suitable feed for your horse, you may have noticed that some of those designed for performance horses contain natural vitamin E. There is no doubt that providing a suitable amount of vitamin E helps to support health and performance, but could the source of vitamin E in your horse’s diet also have an effect?

Why is vitamin E so important?

Vitamin E is an essential, highly powerful antioxidant and plays a key role in supporting muscle and immune health. Antioxidants help to prevent cell damage caused by free radicals. All living cells, including muscle cells, use oxygen leading to the production of molecules called free radicals. When production of free radicals exceeds antioxidant capacity (oxidative stress), cell damage can occur.

Sources of vitamin E in the diet

Whilst free access to green grass may provide sufficient vitamin E for light work (sometimes more), levels in hay and haylage may be negligible - published requirements are also considered to be minimum requirements rather than being optimum. Taking all of this into consideration, many horses need or may benefit from additional vitamin E in their diet.

field being cut for hay

Natural vs. synthetic vitamin E

Natural and synthetic sources of vitamin E differ in their bioavailability – a term used to describe how much of a substance can be absorbed and used by the body. Natural vitamin E has higher bioavailability and may help to further support muscle and immune health in some horses.

What does the science say?

In 2019 SPILLERS, in collaboration with the Universities of Georgia and Kentucky, set out to investigate the potential benefits of synthetic vs. natural vitamin E in exercising horses. Eighteen horses were divided into three diet groups

  1. Hay plus grain and 1000iu of synthetic vitamin E
  2. Hay plus grain and 4000iu of synthetic vitamin E
  3. Hay plus grain and 4000iu of natural vitamin E

All horses completed a standardised exercise test before and after a six-week training programme. The blood vitamin E levels remained within acceptable limits in all horses.  However, the horses fed natural vitamin E: 

-Had higher levels of vitamin E in their blood at most time points than both other groups

-Showed less evidence of oxidative stress post exercise compared to those fed lower levels of vitamin E   

-Showed less change in AST concentrations with exercise and lower concentrations post exercise likely reflecting less muscle damage

 -Showed less reduction in stride duration in the final exercise test - stride duration reduced in all horses in the second test compared to the first but to a lesser extent in the horses fed natural vitamin E

Imogen Murray cross country eventing showing the importance of vitamin E in the diet

What does the science mean?

This study suggested that feeding natural vitamin E may offer health and performance benefits in performance horses.

Is it time to forget about synthetic vitamin E?

Definitely not! Synthetic vitamin E has been helping to meet the horse’s requirements safely and effectively for decades – published requirements are also based on synthetic vitamin E. However, for horses in hard work, including both natural and synthetic sources of vitamin E may help to support optimum health and performance.

For more advice on feeding your competition horse contact the SPILLERS Care-Line.


Fagan MM, Adams A, Harris P, Krotky A, Duberstein KJ. Cytokine and oxidative stress response to vitamin E supplementation in exercising horses. 26th Equine Science Society Symposium, Asheville, NC, June 3 – 6 2019. J Equine Veterinary Science;76:48-9