The Importance of Vitamin E

Vitamin E. You've seen it marketed as a solution for everything from neurological disorders to muscle disease and yes, there are even claims that it can clear EPM. While Vitamin E deficiencies can absolutely contribute to serious neuromuscular disorders, it is not a cure-all, and it won't treat an active EPM infection.

That said, Vitamin E is one of the supplements I most commonly recommend, typically alongside a serum Vitamin E blood serum test done by your vet, and for good reason. Many horses have a mild deficiency simply due to decreasing pasture quality and limited grazing access. It's one of the few supplements where the evidence for routine use in horses with restricted pasture access is genuinely solid.

Vitamin E is essential for numerous physiological processes. It serves as a potent antioxidant, supports normal gene expression, helps prevent inappropriate platelet clumping, and protects the walls of your horse's cells from oxidative damage.

Beyond its antioxidant role, evidence suggests that Vitamin E supplementation supports immune function, with research showing improved immune response and enhanced bacterial killing by immune cells in horses receiving supplementation. For a performance horse heading into show season, that immune support is worth noting.

Now for the part that matters most for those of you with horses in work. Vitamin E deficiency doesn't just affect sick horses, it can quietly undermine the performance, recovery, and neurological function of otherwise healthy horses too.

Some signs of Vitamin E deficiency are tragic and obvious. Others are subtle and easy to miss. Let's get into it.

There are quite a few neuromuscular diseases associated with Vitamin E deficiency, spanning a broad range of clinical presentations. I won't be covering all of them here, but I will discuss three of the most significant and well documented:

• Equine Motor Neuron Disease (EMND)

• Equine Neuroaxonal Dystrophy / Equine Degenerative Myeloencephalopathy (eNAD/EDM)

• Vitamin E Deficient Myopathy (VEM)

All three have evidence supporting Vitamin E deficiency as a primary contributing factor.

Equine Motor Neuron Disease (EMND)

EMND is a progressive motor neuron disease typically caused by prolonged vitamin E deficiency, usually with clinical symptoms presented after 18 months of deficiency. The disease disrupts signals from the brainstem to the muscles in many ways resembling ALS (Lou Gehrig’s disease) in humans. It commonly appears around 15 years of age.

 Clinical signs include:

• Muscle twitching

• Muscle atrophy

• Weakness

• Abnormal weight loss

The prognosis is sobering. With vitamin E supplementation, the only known treatment, approximately 40% of horses improve, 40% stabilize, and 20% progress in severity. Horses that stabilize can go on to have a good quality of life but are unfit for performance. Horses diagnosed with EMND are not safe for riding.

This is why prevention matters. EMND is largely avoidable with adequate Vitamin E.

Equine Neuroaxonal Dystrophy (eNAD) / Equine Degenerative Myeloencephalopathy (EDM)

eNAD and EDM are clinically indistinguishable from one another. Both involve abnormal changes to select neurons in the nervous system, with lesions appearing in different areas depending on the specific disease type. Affected horses vary in sex and breed, but onset typically occurs between birth and 36 months of age, with most clinical signs appearing between 6 and 12 months.

Clinical signs include:

• Poor proprioception — difficulty sensing where their limbs are in space

• Gait abnormalities

• Incoordination, particularly while turning

Sadly, once clinical signs appear there is no reversal. Definitive diagnosis can only be made through post-mortem examination of the brainstem and spinal cord, this means many cases go unconfirmed during the horse's lifetime.

Horses with suspected eNAD/EDM are not safe to ride. Due to the genetic basis of these conditions, affected horses are also not suitable for breeding. Horses with mild clinical signs may be managed as pasture companions.

Prevention is the only tool we have. For horses without access to fresh pasture, Vitamin E supplementation should begin as early as possible — ideally before deficiency has a chance to take hold.

Vitamin E Deficient Myopathy (VEM)

VEM has the clinical symptoms of EMND but without the characteristic muscle atrophy in the muscles along the horse’s spine that defines EMND. Affected horses show low levels of vitamin E in muscle tissue but serum levels were inconsistent making early detection through serum testing valuable.

The good news? When caught early, VEM is reversible and most horses respond well to vitamin E supplementation and make a full recovery. Some research suggests VEM may represent an early stage of EMND, but more studies are needed to confirm that relationship.

This is why testing matters. A simple serum Vitamin E test can catch deficiency before it progresses to something irreversible.  

Vitamin E deficiency is associated with some truly devastating diseases but in many cases it is preventable.

The foundation is simple: give your horse access to quality pasture whenever possible. Fresh grass is the best natural source of Vitamin E. When pasture access is limited, supplementation is highly recommended.

I recommend an annual serum Vitamin E test. I like to pair it with spring vaccinations, so it becomes part of your routine care rather than an afterthought.

And if you notice your horse performing poorly, losing muscle, or dropping weight unexpectedly, don't wait. Work with your veterinarian to find the cause. Caught early, many of these conditions are manageable or reversible. Caught late, they may not be.

Stay curious. 🐴

References:

1.     Finno, C.J. and Valberg, S.J. A Comparative Review of Vitamin E and Associated Equine Disorders. Journal of Veterinary Internal Medicine, 2012, 26: 1251–1266.

2.     Finno, C.J. and Valberg, S.J. How to Effectively Supplement Horses with Vitamin E. AAEP Proceedings, 2018, Vol. 64: 469.