Why Does My Horse Have Diarrhoea?

What can cause loose droppings, which warning signs are an emergency and why you should speak to your vet as soon as your horse has diarrhoea.

Quick Answer

Speak to your vet as soon as your horse has diarrhoea, so the cause can be found and dealt with quickly.
Sudden, severe, watery diarrhoea in a dull, lethargic horse, or one with a high temperature, is an emergency, so phone your vet or an out-of-hours emergency vet straight away.
Any diarrhoea in a foal needs a call to your vet the same day, and straight away if the foal is quiet, off its milk or has a high temperature.
Causes range from a feed change, stress or medicines to infections and worms, and sometimes no cause is found.
Keep an affected horse away from other animals and wash your hands well, because some causes can infect people.

When your horse has diarrhoea, it is hard to know whether it is a minor upset or something serious. A UK vet-group fact sheet says it is a common problem in adult horses and mostly harmless. However, it adds that in very rare cases it can be fatal, so it must be taken seriously and investigated by your vet.

This guide covers the causes that UK sources describe, the signs that make diarrhoea an emergency and what you can safely do while you wait for your vet. It also looks at foals, which need extra care.

Chestnut horse standing behind a wooden fence in a green paddock – speak to your vet as soon as your horse has diarrhoea

Why a horse has diarrhoea: the main causes

Diarrhoea means loose or watery droppings, usually passed more often than normal. In both acute and chronic diarrhoea, the initial cause damages the gut wall, so the gut cannot absorb water as it should.

Often a definite cause is never found. In one study mentioned by a UK vet group, only 30 percent of cases ended up with a clear diagnosis. The causes below are ones that UK sources describe.

A change in feed or routine

Acute diarrhoea can follow a change of routine, such as a new feed. A sudden diet change can upset the gut bacteria and let unwanted bacteria overgrow.

Because of this, many horses recover very quickly. Even so, you should still speak to your vet rather than assume it will settle.

Fresh spring grass

Horses often get diarrhoea after moving onto fresh green grass. The droppings are usually very green and watery, and some horses have it every spring.

One UK source says it normally settles within about 24 hours, especially if the horse goes back to its usual diet. Even so, speak to your vet as soon as it starts, and phone straight away if it does not settle or your horse seems unwell.

Stress and travel

Some horses develop diarrhoea when travelling. Your Horse magazine describes this as usually a stress response.

Medicines

Antibiotics can disrupt the healthy bacteria in the bowel and cause diarrhoea. Worming treatments and some painkillers are also listed as possible triggers.

For this reason, do not give any medicine to a horse with diarrhoea unless your vet says so. If your horse needs oral antibiotics, tell your vet about any past reactions. Your vet can then choose a different treatment or add gut-protecting measures.

Horses eating hay at a tractor-tyre hay feeder in a paddock – a sudden feed change is one reason a horse has diarrhoea

Infections and acute colitis

Colitis is inflammation of the large colon. Well-documented causes include bacterial infections such as Salmonella and Clostridium, and treatment with antibiotics.

Equine coronavirus has also been identified in adult horses in the UK. It can cause fever, loss of appetite and colic, with or without diarrhoea. Treatment is supportive and most horses recover.

Colitis is serious and can be life-threatening, because affected horses can quickly become dehydrated and toxic. Very little UK data exists on colitis in adult horses, and the signs are often similar whatever the cause, so your vet needs lab tests to look for the cause.

Worms

Larval cyathostominosis, a worm-related condition, has long been recognised as a cause of weight loss and diarrhoea. The Royal Veterinary College says cases seem to be seen more often, which could be linked to increasing wormer resistance.

Worm egg counts every three months are one way to keep track. For more, see Worming Your Horse.

Sand in the gut

Sand enteropathy depends on where you live, and it can cause either acute or chronic diarrhoea. A faecal test for sand is described as notoriously inaccurate, so your vet may need abdominal X-rays to confirm it.

Free water in the droppings

One UK vet-group sheet notes that horses are often reported to have a "free water" phase when passing droppings. It says there is no clear cause, although the way fibre is digested in the colon has been suggested.

Only one source describes this, so ask your vet to rule out other disease first.

Diarrhoea in foals

A foal's immune system is less developed than an adult's. As a result, foals pick up infections more easily and can become sicker more quickly.

Horse & Hound advises that any form of diarrhoea in a foal justifies contacting your vet the same day. If a foal has a high temperature, is reluctant to feed or seems quiet and depressed, get vet advice immediately.

"Foal heat" diarrhoea is common in the first couple of weeks. Sources differ on how harmless it is, and one says it can still cause illness and dehydration around 5 to 15 days after birth. For that reason, call your vet if you see it.

Threadworms can pass through the mare's milk and cause diarrhoea in the foal. Adult worming plans are not suitable for foals, so ask your vet what to do.

Signs to look for with diarrhoea

Droppings can range from semi-solid to watery. You may also see the horse straining, or droppings stuck to the tail and down the legs.

Watch for other changes too, because these help your vet decide how urgent it is:

Colic signs such as pawing, lying down more than usual, rolling, kicking at the belly or looking at the flank
Not eating, or dullness and lethargy
A raised temperature (World Horse Welfare gives 37.5 to 38.5°C as the normal range for an adult horse)
Swelling under the belly or on the lower legs
Fresh blood in the droppings, or an unusually foul smell
Weight loss

Emergency: Contact a Vet Immediately If…

The diarrhoea is severe, watery and came on very quickly, and your horse is dull, lethargic or has a high temperature.
The diarrhoea comes with colic signs, signs of laminitis or a raised temperature.
You see swelling under the belly or on the lower legs.
There is blood in the droppings.
Your horse shows signs of dehydration (see Dehydration in Horses).
A foal has diarrhoea and is quiet, off its milk or has a high temperature.

Phone your vet or the nearest out-of-hours emergency vet straight away. Colitis can make horses dehydrated and toxic very quickly.

When to Contact Your Vet

Speak to your vet as soon as your horse has diarrhoea, even if it is still bright and eating.
Phone the same day for any foal with diarrhoea.
Tell your vet about any recent feed change, medicine, travel or worming.
Tell your vet if the diarrhoea keeps coming back or your horse is losing weight.

UK sources advise speaking to your vet as soon as diarrhoea starts. Do not wait to see whether it clears up.

What to do while you arrange the vet

Phone your vet first. Then, while you wait for advice, these steps from a Horse & Hound first-aid feature (first published in 2004) are sensible:

Stable the horse away from other animals.
Offer good hay and plenty of water, and encourage the horse to drink.
Avoid lush grass and concentrate feeds.
Keep the tail and hindquarters clean to protect the skin.
Take care with hygiene and wash your hands well afterwards.

Hygiene matters because some causes, including Salmonella and clostridial disease, can infect people. Take extra care if anyone caring for the horse has a weakened immune system.

Do not give antibiotics, painkillers or wormers yourself. Some of these can cause diarrhoea, and the cause needs to be found first. Ask your vet about electrolytes or probiotics rather than starting them on your own.

How vets investigate and treat diarrhoea

UK vet-group guidance says a full blood panel should be run in all cases. Your vet may also test droppings for worm eggs, sand and bacteria.

In many cases no precise cause is found, which limits specific treatment.

In mild cases, treatment may be as simple as dietary changes and time. More serious forms need hospitalisation and intensive care. Treatment may include fluids, electrolytes, probiotics and pain relief, but that is for your vet to decide.

Acute colitis is described as the most severe form and can be fatal. This is why early vet contact matters.

How to reduce the risk of diarrhoea in horses

Not every case can be prevented, but Your Horse magazine suggests these steps to lower the chance that your horse has diarrhoea:

Change feeds gradually, including a new batch of hay, by mixing new with old.
Carry out worm egg counts every three months.
Tell your vet about any previous reaction before oral antibiotics are used.

For weight changes, see Why Is My Horse Losing Weight?

How Pet Med Direct Can Help

Diarrhoea in a horse is a situation for your vet first. Please phone your vet before you buy or give anything, and follow the advice you are given.

Once your vet has advised you, you can browse our equine range. If your vet prescribes a medicine, you can read how pet prescriptions work. Prescription-only medicines (POM-V) are supplied solely against a valid prescription from the horse's own vet.

Some pet medicines require a valid veterinary prescription. Pet Med Direct can only supply prescription medicines after the prescription has been checked. Always follow your vet's advice and the directions on the medicine label.

Frequently Asked Questions

Is diarrhoea in horses an emergency?

It can be. Sudden, severe, watery diarrhoea with a dull, lethargic horse or a high temperature needs immediate veterinary attention. Even milder diarrhoea should be discussed with your vet as soon as it starts.

Why does my horse get loose droppings on spring grass?

Horses often get green, watery droppings after moving onto fresh grass, and some do so every spring. One UK source says it normally settles within about 24 hours if the horse goes back to its usual diet. Even so, speak to your vet as soon as it starts, and phone straight away if it does not settle or your horse seems unwell.

Is foal heat diarrhoea normal?

It is common, but sources disagree on how harmless it is. Because it can still lead to illness and dehydration, the safest approach is to call your vet the same day for any foal with diarrhoea.

Can I catch something from a horse with diarrhoea?

Some causes, including Salmonella and clostridial disease, can infect people. Take care with hygiene and wash your hands, keep the horse away from others and take extra care around anyone with a weakened immune system.

Related Equine Health Guides

Sources and Further Reading

This article was researched from the sources listed above. It is general information for horse owners and is not a substitute for advice from your own vet.

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This article is for informational purposes only and does not constitute veterinary advice.
If you are concerned about your horse’s health, please consult a qualified veterinarian.