Horses on pasture may be affected by equine motor neuron disease.
Authors: McGorum B C, Mayhew I G, Amory H, Deprez P, Gillies L, Green K, Mair T S, Nollet H, Wijnberg I D, Hahn C N
Journal: Equine veterinary journal
Summary
# Equine Motor Neuron Disease in Grazing Horses: A European Perspective Equine motor neuron disease (EMND) has traditionally been associated with poor forage access and vitamin E deficiency in North American populations, yet this 2006 European case series challenges that assumption by documenting EMND in 13 of 32 affected horses (41%) that maintained part- or full-time access to lush pasture. Despite median grazing durations of 12 hours daily—and notably, five horses grazing for at least 23.5 hours continuously—all affected grazing horses presented with low plasma/serum vitamin E concentrations at clinical onset. The findings suggest that inadequate vitamin E intake alone cannot explain EMND development in these cases, and abnormal vitamin E bioavailability or excessive utilisation may underlie both disease manifestation and depressed serum levels regardless of forage quality or availability. Clinicians should avoid dismissing EMND as a differential diagnosis simply because horses have access to apparently nutritious pasture, and may need to investigate whether factors beyond simple vitamin E insufficiency—such as absorption defects or increased metabolic demands—contribute to disease pathogenesis in grazing populations. This work highlights important regional differences in EMND epidemiology and warrants further investigation into the mechanisms driving vitamin E dysfunction in pasture-kept horses presenting with motor neuron signs.
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Practical Takeaways
- •Do not rule out EMND in grazing horses with full-time pasture access—vitamin E deficiency can occur despite apparently adequate herbage intake due to bioavailability issues
- •Monitor vitamin E status in all horses showing signs consistent with EMND, regardless of grazing management, and consider supplementation even in grass-fed animals
- •Recognize that vitamin E status in grazing horses may reflect abnormal metabolism or utilization rather than dietary intake alone, suggesting investigation of underlying metabolic factors
Key Findings
- •13 of 32 horses (41%) with EMND had part- or full-time access to grass-based pasture, contrasting with North American literature emphasizing limited herbage access as a risk factor
- •All grazing horses with EMND had low vitamin E status despite apparently adequate pasture intake, suggesting abnormal bioavailability or excessive vitamin E utilization rather than simple dietary insufficiency
- •5 horses were at pasture for ≥23.5 hours daily, with 2 maintained year-round at pasture, yet still developed EMND with low vitamin E levels
- •EMND diagnosis should not be excluded based on full-time lush grass access; inadequate vitamin E intake was probably not the sole causative factor