Equine grass sickness.
Authors: Pirie R S, Jago R C, Hudson N P H
Journal: Equine veterinary journal
Summary
Equine grass sickness (EGS) is a polyneuronopathy with devastating effects on both central and peripheral nervous systems, almost exclusively striking grazing horses and triggering characteristic clinical signs rooted in autonomic and enteric nerve degeneration. The severity of disease correlates directly with the extent of neuronal loss in the myenteric and submucous plexuses; acute and subacute presentations involve such extensive degeneration that resulting intestinal dysmotility proves incompatible with survival, whilst some chronic cases with less severe pathological changes may recover. Pirie, Jago and Hudson's comprehensive review synthesises over a century of research literature spanning epidemiology, pathological mechanisms, diagnostic approaches, and treatment options, yet despite this substantial body of work, the precise aetiological trigger remains frustratingly unidentified. Understanding which horses are at heightened risk, recognising the pathognomonic signs early, and distinguishing between disease forms are essential clinical skills for practitioners managing grazing populations. The persistent gap between our understanding of EGS pathophysiology and our ability to prevent or definitively treat it underscores the need for continued epidemiological vigilance and investigation, particularly regarding the specific environmental or infectious factors that might precipitate this devastating condition in susceptible animals.
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Practical Takeaways
- •Recognize that EGS presents with characteristic clinical signs linked to autonomic and enteric nervous system degeneration in grazing horses, with prognosis varying by disease form
- •Understand that acute and subacute EGS cases have poor survival due to severe intestinal dysmotility, while some chronic cases may survive with less severe neuronal damage
- •Be aware that despite extensive investigation, the underlying cause of EGS remains unidentified, limiting preventive strategies
Key Findings
- •EGS is a polyneuronopathy affecting central and peripheral nervous systems that almost exclusively affects grazing horses
- •Disease severity correlates with extent of neuronal degeneration in myenteric and submucous plexuses, with acute/subacute forms causing fatal intestinal dysmotility
- •Chronic forms of EGS with less severe neuronal degeneration have better survival rates than acute presentations
- •Despite over 100 years of research, the precise aetiology of EGS remains unknown