Equine grass sickness

Equine grass sickness (EGS) is a debilitating and usually fatal disease which commonly presents as impaired activity of the gut, caused by nervous system damage, which prevents food from travelling through the digestive system properly. 

Cases are common in northern European countries, particularly Great Britain. The disease occurs almost exclusively in horses with access to grass, but even though the condition was first identified around 1909, the true cause of EGS remains unknown. 

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The disease can present as acute (sudden onset), subacute (milder clinical signs) and chronic (slow onset). 

Symptoms of EGS include: 

• Absence of gut sounds 
• Increased heart rate 
• Gastric reflux (food out of nostrils) 
• Colic 
• Difficulty swallowing 
• Rapid otherwise unexplained weight loss 
• Tucked up abdomen 
• Drooping eyelids 
• Muscle tremors.  

Chronic cases can survive around 40-50% of the time with intensive nursing. Contact your vet immediately if you suspect your horse is displaying signs of grass sickness.  

Fast Facts guide to Equine grass sickness

This Fast Facts guide includes:

• Clinical signs of the different types of grass sickness
• Treatment of grass sickness
• Risk factors and prevention strategies

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Last updated: 11/8/2026. Advice collated by the World Horse Welfare research and education team and externally reviewed Charlotte Gilbert, BSc, MSc, The Grass Sickness Fund.