Equine Grass Sickness is one of those conditions most of us hope we’ll never have to deal with — but it’s also one we can’t afford to ignore. It’s rare, but devastating. And because we still don’t fully understand why it happens, it can feel especially unsettling. If you’ve ever found yourself worrying about it during spring turnout, you’re not alone. Here’s what you need to know — in plain, practical terms.
What is Equine Grass Sickness?
Equine Grass Sickness (EGS) is a disease that affects the nervous system, specifically the part responsible for controlling the gut. In simple terms, it stops the digestive system from working properly. Food can’t move through the gut as it should, which leads to a build-up, discomfort, and eventually serious complications. It’s not just a digestive issue — it’s a whole-body problem.
There are three forms:
- Acute – comes on quickly and is usually fatal within 1–2 days
- Subacute – slightly slower but still very serious
- Chronic – develops over time, and in some cases, horses can survive with intensive care
What Causes Grass Sickness?
This is the frustrating part — we don’t have a single, clear answer. The strongest theory links grass sickness to toxins produced by a soil-borne bacterium called Clostridium botulinum. But not every horse exposed develops the condition, which suggests there’s more going on.
What we do know is that certain situations seem to increase the risk:
- Grazing, particularly in spring and early summer
- Fields with disturbed soil (harrowing, poaching, recent turnout changes)
- Periods of cool, dry weather
- Horses aged roughly 2–7 years
- Yards where cases have occurred before
It’s also worth saying — it isn’t contagious. One case doesn’t mean it will spread horse to horse.
Symptoms to Watch For
Grass sickness can be difficult to spot early, especially as some signs overlap with colic.
Things that should raise a red flag:
- A horse going off their food
- Dullness or just not quite being themselves
- Mild or persistent colic signs
- Reduced droppings
- Weight loss (more obvious in chronic cases)
- Difficulty swallowing or quidding
- Excessive salivation
- Patchy sweating or muscle tremors
One of the more classic signs is a tucked-up appearance, where the abdomen looks drawn in. If something feels off, trust that instinct and call your vet. With grass sickness, it’s always better to act sooner rather than later.
Can It Be Treated?
This is the part no one likes hearing. There’s currently no cure for Equine Grass Sickness.
- Acute and subacute cases are usually euthanised on welfare grounds
- Chronic cases can sometimes be managed, but it requires intensive, long-term care
For horses with the chronic form, management typically includes:
- Highly digestible, calorie-dense feeds
- Small, frequent meals
- Careful nursing and monitoring
- Time — often months, not weeks
Some horses do recover, but it’s a long road and not always a predictable one.
Reducing the Risk
Because we don’t fully understand the cause, prevention is about risk management rather than guarantees.
Practical steps that may help:
- Introduce turnout gradually, especially in spring
- Provide hay or haylage alongside grazing
- Avoid turning out onto recently disturbed pasture
- Keep grazing consistent — minimise sudden changes
- Avoid overgrazing and maintain good pasture management
- Consider mixed grazing where possible
If your yard has had a previous case, it’s worth having a more tailored plan in place with your vet.
A Final Thought
Grass sickness sits in that uncomfortable space of being both rare and serious — which is why it stays at the back of so many horse owners’ minds. You don’t need to manage in fear of it. But being aware of the signs, understanding when risk is higher, and knowing when to act can make all the difference. If nothing else, take this as a reminder to trust your gut — you know your horse better than anyone.
Last Updated on 17/04/2026