Equine motor neuron disease (EMND) is a neurodegenerative disorder of the lower motor neuron system. The etiology of EMND is unknown, although studies have suggested vitamin E deficiency contributes to the its development. This retrospective study was done to examine whether low plasma antioxidant levels are associated with the risk of EMND. We evaluated whether this association was confounded by season of diagnosis, age, breed and management practices. 314 horses were included in the study, 108 had been diagnosed with EMND. Vitamin A, vitamin E, selenium, and beta-carotene were measured. The only antioxidant with significant association was vitamin E, where EMND cases had decreased concentrations. This supports the involvement of oxidant injury in the pathophysiology. Horses with EMND were significantly older. The age association probably is a result of needing more time for whole body vitamin E levels to be depleted sufficiently. Ongoing research is needed to elucidate these associations.