Diarrhoea is relatively common and a potentially serious condition that affects horses of all ages. In all but the mildest cases it is wise to call your vet to ensure prompt treatment is initiated and more serious conditions are identified before they worsen.

Parasites (worms)

Small roundworms cause disease in young horses following anthelmintic treatment (worming) and can be preceded by weight loss. This can be a fatal condition, but can be prevented by regular worming and removing droppings from pasture
Large roundworms can cause colic and ill thrift at any age. But is easily prevented by routine anthelmintic treatment (worming) and removing droppings from pasture. Routine worm faecal egg count analysis can monitor the effectiveness of your worm prevention and allow you to target your regime at high risk individuals and times of the year.
Tapeworms can cause diarrhoea and ill thrift.

Colitis (inflammation of the colon)

Colitis can be infectious or non-infectious in origin. Infectious causes include salmonella and clostridial infections. These are both life-threatening and can be transmitted to humans. They usually develop suddenly and are accompanied by signs of colic. If infectious colitis is suspected the horse will need to be isolated and may require intensive nursing. Non-infectious causes include right dorsal colitis, which is inflammation of the colon commonly caused by long-term drug administration, e.g. Bute (phenulbutasone).

Grain overload

Usually accidental exposure and consumption of large quantities of concentrate feed. This results in disruption of the normal gut flora and systemic endotoxaemia. Diarrhoea and laminitis develop secondarily and can be fatal. Seek veterinary attention urgently if your horse breaks into a feed store.

Inflammatory bowel disease (IBD) and lymphoma (cancer)

IBD causes weight loss and diarrhoea that progress slowly over several months. Horses can be treated with steroids, but the condition is not curable and the prognosis is poor.

Dental disease

If a horse has poor teeth it will not be able to chew its food properly, this can result in diarrhoea due to inadequate digestion of roughage. This can be prevented by routine dental care.

Sudden dietary changes

Horses gut flora adapts to digest the food they are provided with. If that diet is changed suddenly the gut flora will not be prepared and the food eaten will not be adequately digested. To prevent this ensure that all diet changes are made slowly, usually over a 7-10 day period.

Other causes

Any disturbance of the gastrointestinal tract may result in diarrhoea.

If you notice your horse has diarrhoea, you should call your vet for advice.
If the horse is bright and eating well, and has had diarrhoea for a while, it may not be necessary to have an emergency call out, but if the horse is depressed or has suddenly developed diarrhoea, or is showing any signs of colic, then an emergency call out will probably be necessary. You should discuss this with your vet when you call them.
Whilst waiting for your vet to arrive, keep the horses hind quarters clean, do not feed sugar beet or vast quantities of other concentrates. Try to avoid rich haylage or silage, and if the horse is showing signs of colic remove all feed until your vet arrives.

Clinical examination

  • Infectious colitis (inflammation of the colon) often causes a fever.
  • In cases of chronic diarrhea horses can develop ventral oedema (fluid collection along belly).
  • Horses should be assessed for signs of colic and systemic infection.

Dental examination

  • Check for fractured teeth, sharp points, evidence of tooth root infections, or any other cause of poor mastication (chewing).

Faecal samples

  • Culture for bacteria, e.g. Salmonella.
  • Worm faecal egg count to assess worm burden.
  • Examine faeces for evidence of worm larvae.
  • Examine faeces for evidence of long fibres indicating poor chewing.

Blood tests

  • Can confirm presence of a high tapeworm burden.
  • Signs of infection and inflammation.
  • Protein levels in blood are low in horses with diarrhoea.

 Abdominal ultrasound

  • Will show evidence of gut thickening and inflammation.
  • The gut can only be assessed in small sections due to the large size of the equine abdomen.
  • Ultrasound scanning is something that your own vet may not be able to do as a powerful ultrasound machine is required.
  • Your horse may require referral to a specialist centre for an abdominal scan.

Yes, in cases of diarrhoea, the underlying condition needs to be treated, e.g. rasp teeth to remove sharp points.
If the diarrhoea is severe the horse’s hydration status will need to be maintained, so fluid therapy may be required.  This can be given orally via a stomach tube or into the vein via a drip. If your horses is severely dehydrated referral to a specialist centre may be required.
Any ongoing causes of diarrhea should be removed. If your horse is on any drugs for other conditions, e.g. Bute or antibiotics, it may be necessary to stop these treatments. Antibiotics kill most bacteria, including the friendly bacteria, in the gut, for this reason antibiotics aren’t usually given to treat diarrhoea in horses.
Steroids may be required if gut inflammation is the cause of the problem. Steroids are the best anti-inflammatory drug available, however they do carry side effects and may not necessarily cure the problem.
In severe cases of diarrhea when horses are very sick plasma therapy can be used to replace lost protein. This requires intensive nursing and would only be undertaken in extreme situations.

The main aim is to avoid sudden changes in your horse’s diet. It is very important to feed horses consistently; any sudden changes in the diet will disrupt the gut flora and could cause diarrhoea.
Routine worm prevention is essential, this includes removing droppings from the paddock every couple of days which reduces exposure to worms, and routine anthelmintic treatment (worming) will reduce any existing worm burden. The best way to manage a yard is for all the horses to be wormed at the same time with the same product and for worm faecal egg count analyses to be carried out intermittently to monitor effectiveness of the treatment.
Routine dental care is also very important, so ensure that your horses teeth are checked annually or more frequently in older horses or if dental disease is evident. Ensure that the teeth are checked by a qualified equine dental technician or a vet.