Sometimes your horse gets the runs when you travel to a horse show, or when the spring grass gets lush, so you don’t think of diarrhea as a big deal. But Dr. Katharina Lohmann, associate professor of Large Animal Medicine at the Western College of Veterinary Medicine, says that can be a mistake. “We teach our students that acute diarrhea is serious. It’s an emergency.”

Diarrhea may be the main symptom of many potentially dangerous conditions such as infections, parasite overloads, and toxins.

Diarrhea Defined

The first challenge in dealing with diarrhea, Lohmann says, is defining it. Horses normally have frequent poops throughout the day, and the consistency can vary quite a bit depending on their diet and other activities. Horse owners need to be aware of what’s normal for each particular horse.

“If the horse is having somewhat more frequent bowel movements, but they are still of normal consistency, that’s less of a concern,” Lohmann says. “But if they are very loose and watery, and especially if they are loose and significantly more frequent, I would strongly recommend consulting with a veterinarian.”

Signs of illness combined with diarrhea make for an emergency situation. Generally, symptoms of acute diarrhea include:

  • loose, watery, frequent stools
  • fever
  • lethargy/depression
  • loss of appetite
  • loud gut sounds
  • dehydration
  • signs of abdominal pain
  • weakness
  • edema in lower limbs and abdomen

Chronic diarrhea over a longer period of time will additionally manifest as:

  • weight loss
  • poor appearance (dull eyes, rough hair coat)


The most serious causes of diarrhea are bacterial or viral infections (i.e. Potomac horse fever, salmonella, clostridium difficile, coronavirus). These are not only potentially dangerous for the horse, but may be passed on to other horses – and in some cases, to humans as well. Because of that, Lohmann’s recommendations for management focus not just on curing the horse that is sick, but preventing the spread of the disease.

Whether the horse is going to be brought to a veterinary hospital or seen during a farm visit, the animal should be kept isolated from others. “If the horse is pastured, we recommend leaving him in that field and moving the other horses to a clean field,” says Lohmann. “Be sure to keep the manure away from the other horses and away from the feed and water.” People working around the horse should wear coveralls and ideally gloves, wash their hands frequently if not wearing gloves, and clean their boots before going indoors or working with other horses. If you take the horse to a clinic, expect him to be placed in isolation.

With some diarrheal diseases (such as salmonella infections), there is also a risk to humans, so small children and those with weakened immune systems should be kept away from the area where the horse is stabled.

Lohmann also recommends collecting a large sample of the horse’s feces that can be used for testing, using a clean container with a tight-fitting lid. “One of the difficulties from the veterinarian’s standpoint is that many different infectious diseases have very similar symptoms. If we see the horse who is lethargic and has diarrhea, there are several possible diagnoses, and we really need to do testing to see which it is,” explains Lohmann. That can be costly, and often multiple tests are necessary to determine the problem and decide which medications would be best to treat the illness.

Sometimes, even after extensive testing, no clear answer is found and the veterinarian will need to make treatment decisions based on what has been eliminated and what illnesses are known to be prevalent in the area.

Occasionally, horses develop diarrhea during or following treatment with antibiotics for an infection. The theory behind this is that antibiotics can upset the normal intestinal flora and allow other bacteria to take over, causing diarrhea. It is a rare complication in horses, says Lohmann, but it is a reminder of the need to be cautious about using antibiotics. Ironically, for some bacterial infections causing diarrhea, antibiotics are the best treatment. “This is why it is important to do the testing and talk with the veterinarian,” she says.

Toxins, etc.
Blister beetles are insects that can live in alfalfa hay; if a horse inadvertently eats them, he may develop diarrhea. Other substances that can cause diarrhea include adverse reactions to commonly-used NSAIDS such as banamine and bute.

Horses who ingest sand while grazing or eating hay spread on sandy ground may also develop diarrhea, as the sand is very irritating to their digestive system. Other causes include bowel inflammation, altered intestinal flora, even congestive heart failure and chronic liver disease.

Home Treatment

What can you do while waiting for the vet?

Keeping the horse hydrated is essential. Add electrolyte powder to the water. Fresh water should always be available as well.

“Many people will give their horses Pepto Bismol or similar medications,” says Lohmann. Bio-Sponge is another frequently-used intestinal adsorbant. “For these types of medications to work, you would often need to give a much larger volume than you can give without using a stomach tube – and stomach tubing must only be done by veterinarians.” Lohmann suggests owners consult with their veterinarian before administering any medications to their horses.

Another home remedy Lohmann warns against is mineral oil, which can be fatal if the horse aspirates it into his lungs.

Probiotics are sometimes recommended by veterinarians, but Lohmann says that definitive research is still lacking in this area and some studies with foals have shown they did worse when given certain probiotics.

Veterinary Care

Your vet will try to identify the cause of the diarrhea and treat that if possible. Because dehydration and electrolyte imbalance is a major concern for any horse with diarrhea and the horse’s inflamed gut may not absorb water well, IV-fluid therapy is standard. Some horses who have lost protein may also be given IV plasma. Founder is also a common complication; veterinarians often try to pre-empt this by icing the horse’s feet.

One rather unusual treatment has shown some good results in humans with clostridial diarrhea and has also been used in horses: fecal transplants. Feces collected from a healthy horse is transplanted into the bowel of a horse with acute diarrhea; the idea is that the healthier bacteria will then take over and eliminate the ones making the horse ill. “There is not a lot of research in horses, but anecdotally, it’s been effective in some cases,” says Lohmann. One challenge is that even apparently healthy horses may actually have some degree of infectious bacteria in their feces, so careful testing is needed.

Lohmann’s main message to horse owners is to take diarrhea seriously. If your horse seems ill in other ways, or if the diarrhea lasts more than a brief period, contact your vet right away. Those watery, frequent stools can be a true emergency, and prompt treatment increases the odds of a good outcome.