Vitamin E deficiency can contribute to clinical neurologic disease in horses. | Hannah Kleckner, Penn Vet New Bolton CenterVitamin E functions as an important and potent antioxidant supporting neuromuscular health in horses, said Sarah F. Colmer, VMD, Dipl. ACVIM, a fellow in large animal neurology at the University of Pennsylvanias New Bolton Center, in Kennett Square, during her Burst presentation at the 2025 American Association of Equine Practitioners Convention, held Dec. 6-10, in Denver, Colorado.Horses typically get vitamin E from fresh green grass. Levels of vitamin E degrade rapidly in stored hay. In addition, individual animal factors might affect horses vitamin E blood levels, such as increased metabolism or malabsorption.Equine Motor Neuron DiseaseIf horses havent consumed enough vitamin E, they can develop equine motor neuron disease (EMND), a sporadic neurodegenerative disease characterized by muscle wasting, weight loss, muscle fasciculations (involuntary contractions of small muscle fibers), excessive recumbency (lying down), weight shifting, and a characteristic elephant on a ball stance in some cases. We are seeing less of EMND because our knowledge of vitamin E importance has improved, said Colmer. This condition is typically observed in horses with a history of limited access to pasture.Approximately 45% of EMND horses treated with vitamin E respond, but many horses must be euthanized. In some cases horses might simply stabilize and neither decline nor improve.Vitamin E Responsive Myopathy in HorsesAnother disease, vitamin E responsive myopathy (VEM), presents with less severe signs of EMND, often with a history of poor performance, said Colmer. In this population, not all horses have low serum vitamin E levels at the time of testing.Biopsies of the sacrocaudalis dorsalis medialis muscle, located at the base on the horses tail, show what appear as moth-eaten fibers suggestive of VEM. Affected horses can respond very well to vitamin E supplementation, some making complete recoveries.Vitamin E and eNAD and EDMThe neurogenerative diseases equine neuroaxonal dystrophy(eNAD) and equine degenerative myeloencephalopathy (EDM) cause chronic symmetric, mild-moderate ataxia, and sometimes behavior changes. No pre-mortem diagnostic test exists for this condition, and veterinarians do not believe eNAD or EDM result from low vitamin E intake alone.It appears to be multifactorial, possibly affected by both genetic makeup of the horse, the environment (pesticides, for example), and the nutritional component, Colmer explained. Not all affected horses respond to vitamin E supplementation.Vitamin E Supplementation in HorsesWhen managing horses with any of these conditions or neuromuscular concerns, Colmer recommended increasing vitamin E intake to achieve blood levels between 3 and 6 micrograms per milliliter (g/ml). Note that this is higher than the reference range, which starts at 2 g/ml, and reference ranges, units, and targets differ between laboratories (anything below 2 g/ml is considered low, but this depends greatly on the individual horse).I often start supplementing vitamin Edeficient horses with 5,000 IU vitamin E per day and recheck blood vitamin E levels in one to two months, Colmer said. Further adjustments may be needed, so rechecking is recommended. Colmer said natural sources of vitamin E are usually preferred over synthetic.Take-Home MessageHorses need vitamin E to support their neuromuscular health, and inadequate intake can contribute to several neuromuscular diseases. Early recognition and appropriate supplementation of vitamin E can significantly improve outcomes in some conditions, and regular monitoring of vitaminE levels in the blood helps veterinarians guide effective supplementation and management.