Equine Grass Sickness: Signs, Weather Risk and UK WhatsApp Alerts

What is equine grass sickness?

Equine grass sickness (EGS) is a rare but usually fatal disease that damages the nerves controlling a horse's gut, so the digestive system slows down or stops. It mostly strikes grazing horses, ponies and donkeys in Britain and northern Europe, the cause is still unknown, and only about 20% of affected horses in Britain survive.

Vets also call it equine dysautonomia. The damage hits the autonomic nervous system, the part that runs automatic jobs like swallowing, gut movement and sweating.

It isn't contagious, so it doesn't pass from horse to horse. Even so, more than one horse on the same premises can be affected, and one horse can die while its field mate stays healthy.

Why grass sickness is in the news in 2026

On October 13, 2026, Your Horse reported that researchers are seeing grass sickness in areas where they wouldn't normally expect it, and more horses are dying after getting it. Experts, including Dr Beth Wells, EGS project lead at the Moredun Research Institute in Scotland, urged owners to learn the signs and sign up for local risk alerts.

That warning follows a cluster in southwest Scotland. In early September, STV and Vet Times reported that Machars Veterinary Services, based in Wigtown in Dumfries and Galloway, had reported multiple local losses to the disease in an area where, it said, cases are usually very rare. The practice suspected that this year's unusual weather played a part.

The Equine Grass Sickness Fund (EGSF), the Moredun-based research charity, says on its fundraising page that at least 62 horses have died from grass sickness in 2026. It also says it is running short of money for research.

The free WhatsApp risk alerts

• What it is: weekly or monthly WhatsApp messages with a grass sickness risk prediction for the area you choose.
• Who runs it: the Equine Grass Sickness Fund, part of the Moredun Foundation, with research partners.
• Why weather: research links more cases to big temperature swings, like frosty nights followed by warm sunny days, and to rain breaking a drought.
• How to join: sign up through Moredun's Connect Animal Health site; the EGSF website, grasssickness.org.uk, links to it. The service is currently limited to the UK.

An alert doesn't mean your horse will get sick. It's a cue to review grazing and watch your horses more closely for a while.

Grass sickness symptoms: acute, subacute and chronic

Vets describe three forms, and the signs often overlap. Acute signs can appear very quickly, so it helps to know them before you ever need to.

Signs to know, in plain words

• Trouble swallowing: dropping food, refusing feed or drooling saliva.
• Colic-like pain with a quiet gut: you hear little or no gut noise when you listen at the flanks.
• Patchy sweating: damp patches on the neck, shoulders or flanks for no clear reason.
• Muscle tremors: twitching, often over the shoulders and flanks.
• Droopy upper eyelids: a sleepy or sad look.
• Fast heart rate and a dull, depressed attitude.
• Fluid from the nose: sometimes green, foul-smelling liquid in severe cases, or dry, crusty nostrils in chronic ones.
• Rapid weight loss and a tucked-up, herring-gutted belly.
• Odd stance: chronic cases may stand with all four feet close together.

Because many of these signs look like colic, it's worth knowing the basics in our guide to the early signs of colic. Your vet is the one who tells the two apart.

What causes grass sickness in horses?

Nobody knows for sure, more than a century after the disease was first recorded in Scotland around 1907. One major line of research is whether Clostridium botulinum type C, a bacterium found in soil, is involved. That link has been proposed and is being studied, but it hasn't been proven.

Other pieces of the puzzle researchers are looking at:

• A nerve-damaging toxin made by a microbe in the pasture.
• Soil disturbance, plus soil and plant fungi and bacteria.
• Changes in gut microbes, nutrition, immunity and stress.
• Genetics: a Hungarian study suggested a possible inherited factor.

Almost all cases involve horses with access to grass. A few cases have been linked to hay in horses that weren't grazing.

Who is most at risk?

• Age: young adult horses, most often 2 to 7 years old, though any horse after weaning can be affected.
• Lifestyle: horses kept at grass. Native ponies and cobs are affected most often, mainly because they are more often kept at grass, but all types are at risk, from racehorses to pet ponies.
• Season: cases peak from April to June but happen year-round, and this year's warnings came in late summer and autumn.
• Weather: cool, dry spells with irregular frosts, big temperature swings and rain after drought.
• Place: fields where grass sickness has happened before, and recent moves or changes in pasture or diet.
• Region: Britain has the most cases worldwide, more on the east side than the west, especially in Scotland.

Outside Britain and northern Europe, the disease is rarely reported, with one big exception in South America.

Mal seco in Patagonia

In Argentine and Chilean Patagonia, horses get a disease called mal seco. Researchers consider it the same disease as grass sickness, or one that is extremely similar in its signs and in the nerve damage seen under the microscope.

The WhatsApp alerts only cover the UK for now, but knowing the signs and calling a vet quickly matters wherever your horse lives.

How to lower the risk: a pasture checklist

There is no guaranteed prevention, but the British Horse Society and EGSF suggest these steps:

• Keep grazing to a minimum in fields with past grass sickness cases.
• Avoid disturbing the soil, such as harrowing or digging, where horses graze.
• Don't let fields get grazed down to bare soil or churned into mud.
• Make diet and pasture changes gradually, not suddenly.
• Offer extra forage such as hay alongside grass.
• Pick up droppings by hand where you can.
• Co-graze with sheep or other ruminants if that's practical.
• Ask your vet about a testing-led deworming plan.
• When an alert flags high risk, consider shorter turnout and closer checks.

For more on forage and grazing, see our nutrition guide and hay shortage explainer.

What to do if you suspect grass sickness

Call your vet straight away. Grass sickness can move fast, and there's no safe way to judge it at home.

1. Bring the horse in and keep it quiet and safe.
2. Note which signs you see and when they started.
3. Check heart rate and gut sounds only if you've been taught how (our health basics page covers normal values).
4. Don't give any medicine unless your vet tells you to.
5. Tell your vet about recent field moves, weather or other horses that seem off.

The outlook is honest but hard. Acute and subacute cases don't survive, and vets will discuss humane options. Some carefully chosen chronic cases recover with weeks of intensive nursing, and many go back to normal working lives.

If it happens to your horse, it is not your fault. Dr Wells has said the disease strikes randomly, that it isn't the owner's fault and that the stigma around it needs to go.

What to watch next

• Autumn weather: frosty nights after mild days and heavy rain after dry spells are exactly the patterns the alerts track.
• Reporting: UK owners can report cases anonymously on the EGSF website to build the picture of where and when it strikes.
• The biobank: the Moredun Foundation and EGSF, with British Horse Society support, collect samples from affected horses. Vets can apply to cover sampling costs, so owners pay nothing.
• Research funding: the EGSF says its new research program gives the best chance yet of finding the cause, if it can be funded.

Grass sickness is rare, so there's no need to panic every time your horse looks tired. Knowing the signs, and acting fast, is the best thing any owner can do.