GRASS SICKNESS IN HORSES - Symptoms and prevention

The spotlight on Equine Grass Sickness
Equine grass sickness

Equine Grass Sickness, a condition known now to be caused by a toxin produced by a clostridia bacterium, the same bacteria that, in different circumstances, can cause Botulism. The insurer receives the highest number of claims in June and July however Petplan Equine’s veterinary expert Gil Riley warns that, while the condition is most prevalent between April and September – with a spike in May - it can strike at any time of year. 

“The bacterium lives in the soil and when it spreads onto the grass itself it can be ingested by horses. The toxin that is produced by the bacterium after it has been consumed interferes with the nerves in the horse’s intestine causing severe dysfunction and colic which is almost always fatal” says Gil. 

Grass sickness can present in one of three ways:

•Peracute: The horse is found dead in the field having presumably ingested large amounts of the bacteria.

•Acute:The horse usually  presents at first with moderate abdominal discomfort but a pulse that is abnormally high. 

•Chronic: This is the form of the condition from which affected horses can sometimes recover. It comes on slowly, usually two to three days, and presents as low grade colic with rapid weight loss. Other signs include: a droopy eyelid, dry sticky nasal discharge and faeces balls that are hard and small. 

Recovery from the Chronic form may be possible but only with intensive care and pain relief and providing the horse is still able to swallow; the swallowing reflex can be affected by the toxin and if this happens then even the chronic presentation will be fatal. 


•Avoid introducing new (usually young) stock onto paddocks that have previously produced grass sickness or where the soil has been disturbed – for drainage works for example.

•Avoid a grass-only diet; feed hay in the field or bring horses in at night.

Petplan Equine’s Senior Marketing Executive Charlotte Collyer says: “The statistics speak for themselves and show us that what was previously thought to be a summer-specific condition is something that affects horses throughout the year.”

“We understand an Equine Grass Sickness vaccine is currently being trialled. Until then we want to remind horse owners that prevention is of paramount importance as this is a condition for which there is often no cure” explained Charlotte. 
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For more information on Grass Sickness and how to spot signs and symptoms along with details about the Equine Grass Sickness vaccine trial visit