Equine Motor Neuron Disease Study Guide

Overview and Clinical Importance

Equine Motor Neuron Disease (EMND) is an acquired neurodegenerative disorder affecting the somatic lower motor neurons in adult horses. First described in 1990 by Cummings et al., the disease shares striking similarities with sporadic amyotrophic lateral sclerosis (ALS) in humans, also known as Lou Gehrig's disease. EMND is strongly associated with chronic vitamin E (alpha-tocopherol) deficiency, typically occurring in horses that have been deprived of adequate vitamin E for 18 months or longer.

The disease results in progressive degeneration of motor neurons in the ventral horns of the spinal cord and selected brainstem nuclei, leading to neurogenic muscle atrophy, weakness, and characteristic clinical signs. Understanding EMND is critical for NAVLE success because it represents an intersection of nutrition, neurology, and clinical medicine with diagnostic and prognostic implications.

Etiology and Pathophysiology

Vitamin E Deficiency as Primary Risk Factor

Alpha-tocopherol (vitamin E) is the primary chain-breaking antioxidant that prevents cyclic propagation of lipid peroxidation in cell membranes. Motor neurons are particularly vulnerable to oxidative stress due to their exceptionally long axons and resulting high metabolic demands. Fresh green pasture is the primary natural source of vitamin E for horses, providing approximately 110 IU per kilogram of dry matter.