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Why Does My Horse Have Diarrhea? Tips to Prevent and Treat

Last updated: December 20, 2022

By: Miles HenryFact Checked

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I recently visited a neighbor and noticed one of his horses has diarrhea. He wasn’t sure why his horse contracted the ailment and asked if I knew what could’ve caused his horse’s diarrhea.

Diarrhea in horses is typically caused by bacterial infections, antibiotics, inflammation of the intestines, or internal parasites. Horses with this ailment have loose, watery stools accompanied by frequent bowel movements. Equine diarrhea can cause severe damage and even be fatal.

Horses have delicate digestive systems, and diarrhea is frequently the result when it’s upset. But what are the causes of the disruption, and how can it be prevented and treated?

Picture of a sick horse laying on the ground.

Why horses have diarrhea

Horses get diarrhea for various reasons; sometimes it’s caused by their feed, sometimes it’s caused by a virus or bacteria, antibiotics, and other times it may be caused by parasites or disease that affects the digestive system.

If your horse has diarrhea, you need to take steps to ensure it doesn’t dehydrate. Equine dehydration is a serious condition that causes colic and can be fatal.

Dehydration occurs because the horse’s body isn’t functioning correctly, and critical fluids are not absorbed. When this happens, the fluid passes through the colon and exists as runny poop.

The lack of fluids retained by the animal deprives the body of critical moisture needed for its organs to function correctly.

Bacterial infections

Bad feed and sickness can lead to bacterial infections that cause diarrhea. Salmonella bacteria are the primary culprits causing runny poop, and once it enters a horse’s body, various reasons cause the flora to multiply.

Changes in diet, antibiotics, and colic create opportunities for salmonella bacteria to flourish. Even a microscopic level can cause bad bouts of fluid loss and dehydration, and horses often need IV fluids to recover.

Change effects bacteria

Most horses live with a certain amount of harmful bacteria in their GI tract. However, the bacterial flora remains dormant until their bacteria balance is upset.

What are some things that provoke bacteria to action? It doesn’t take much to tilt the apple cart; dietary changes, antibiotics, transporting, and changing medications can result in diarrhea manifestation.

Recurring colic

Colic and the onset of diarrhea have a reciprocal relationship. They are both a cause and a symptom; a horse with colic is prone to bacterial infections, which leads to diarrhea. Also, horses that have diarrhea are often dehydrated, which is a cause of colic.

Inflammation of the intestines

Often inflammation of the intestines related to the onset of diarrhea is a result of sand ingestion. Horses typically digest minute amounts of dirt from eating off the ground.

The sand irritates the gastrointestinal membranes and causes an adverse reaction, preventing fluids’ absorption. Sand ingestion isn’t the only cause of inflammatory bowel disease (IFB); horses also have adverse reactions to medications.

Two common drugs that are known to cause mild cases of diarrhea are Bute and Banamine. And antibiotics are essential in treating our equine friends, but they often are a cause of diarrhea.

Antibiotic-associated diarrhea (AAD) causes a horse to feel bad and can also be fatal. It’s believed equine antibiotics decrease principal bacteria in the animal’s hindgut, allowing harmful bacterial pathogens to grow.

Intestinal inflammation can also occur when horses develop a reduction of white blood cells, typically associated with other more severe diseases such as cancer. Specific plants are also a cause of inflammatory bowel diseases.

Internal parasites

Strongyle is the parasite that wreaks the most havoc on the equine digestive tract. They cling to blades of pasture grass and are ingested by grazing horses.

Once inside the animal’s stomach, they cling to the horse’s gut’s wall and pierce holes in its lining. The holes create internal leaks, which lead to diarrhea. The adult strongyle, still inside the animal’s digestive tract, lays eggs that pass in the horse’s manure.

Worming programs are a must for horse owners who want to prevent their animals from getting parasites. A good quality product will help kill worms that cause diarrhea and many other harmful varieties.

Picture of a vet checking a horse that has diarrhea,

Diagnosing the cause

If your horse has diarrhea, you may be wondering what could be causing it. There are many potential causes of diarrhea in horses, and it can be tricky to diagnose the exact cause so it can be effectively treated.

For example, sand-induced intestinal inflammation reacts well to treatment; however, some cases need aggressive treatment if your horse can recover.

Physical exam

Start your exam by evaluating your horse’s vital signs and checking its feet for signs of laminitis. Checking for laminitis may seem strange when diagnosing intestinal disease, but laminitis develops in severe cases of bacterial infection.

Also, note if your horse is losing weight explicitly due to its sickness. Horses with diarrhea lose weight because of water loss; however, it is critical to note if their weight loss results from the depletion of fluids or if chronic weight loss is associated with IFB or parasite infestation.

Often when it’s the latter, horses manifest a reduction in their weight before the onset of loose bowels, and the condition persists regardless of the volume of diarrhea.

Some symptoms require immediate attention from a vet. For example, if you notice a high volume of watery diarrhea, your horse is a canidate for IV treatment to replenish lost water and electrolytes.

Perform a simple skin tent test to determine if your horse is dehydrated. Pull the skin at your horse’s shoulder and release; it should return to normal relatively quickly; if it remains extended, then your horse is dehydrated.

Another easy way to check your animal is to look at its mucous membranes and check the capillary refill time. Flip back their lips and check that they are pink, push against their gums and watch how fast they return to their natural color.

Your horse doesn’t have enough fluid if they are pale or white. A failed capillary test is also indicative of bacterial infections. If your horse’s mucous membranes take an unusually long time to refill, you should call a vet.

Veterinarians can run a series of blood tests to help determine the cause of diarrhea. Typically they run a complete blood count (CBC), plasma total protein and fibrinogen, and serum chemistry test.

In addition to a blood test, they may also test the animals’ feces to check for sand, toxins, and strongyle eggs. However, even with all the tests available, it’s often difficult to pinpoint the disease’s exact cause.

Picture of a young horse in training.

Treating diarrhea

If your horse has diarrhea, you may be wondering what to do. Diarrhea can be a serious problem in horses, and treating it as soon as possible is important.

In most cases, the first thing you should do is call your veterinarian because diarrhea can be a sign of a serious health problem. It is important to get professional medical help as soon as possible.

Your veterinarian will be able to determine the cause of diarrhea and recommend the best course of therapy. The type of treatment your horse needs will vary based on the cause of diarrhea and its duration.

If your horse is feeling fine but passing semi-runny stools after changing its diet, then it should recover relatively quickly. Keep an eye on your animal and make sure he continues to drink plenty of water. You may also consider adding electrolyte powder to his water bucket as a precaution.

However, if the animal is passing almost straight fluid or the condition persists for more than a day or two, you need to contact a vet and have your horse checked because it is at risk of colic and dehydration; diarrhea can be fatal, so don’t take any chances.

Preventive measures

One of the most important things you can do as a horse owner is to learn how to prevent diarrhea in horses. Although it may seem like a minor issue, diarrhea can actually lead to serious health problems in horses if it is not treated properly.

One way to prevent diarrhea in horses is to make sure that they have access to clean water at all times. It is also important to feed them a balanced diet and avoid giving them any food that may be contaminated.

If you are unsure about what to feed your horse, consult with a veterinarian or equine nutritionist. Another way to prevent diarrhea is to keep their living quarters clean and free of any potential contaminants.

Regularly clean their stalls and ensure their pasture is free of manure and other waste. Finally, horses should be vaccinated against common diseases that can cause diarrhea.

Commercial probiotics advertise their products’ effectiveness in preventing diarrhea; however, I haven’t seen any results that indicate they are helpful.

In reality, diarrhea is inescapable, but there are some steps you can take to reduce the risk that your horse develops the problem. Here is a list of things to keep in mind:

  1. Have your horse on a deworming program
  2. Make available a fresh and clean water source,
  3. Gradually introduce new feed,
  4. Limit grazing time when the grass is lush,
  5. Keep your pastures in good shape and sprayed,
  6. And please make sure all your horses are current on their vaccines

Following these tips can help prevent your horse from getting diarrhea.


If your horse has diarrhea, it must be attended to immediately. Hopefully, it’s a mild case that can be remedied with the passage of time and a bucket of water.

The causes of diarrhea vary, and it’s challenging to prevent. Contact your vet if your horses’ diarrhea is excessive, watery, or persists for more than 24 hours. If you’re unsure, don’t take any chances; call the vet.


Can ulcers cause diarrhea in horses?

Yes, ulcers can cause diarrhea in horses. Ulcers in the stomach or small intestine can lead to inflammation and irritation of the lining of these organs, which can cause diarrhea.

Can hay cause a horse to have diarrhea?

It is possible for hay to cause diarrhea in horses. There are several factors that can contribute to hay-induced diarrhea in horses, including the quality of the hay, the type of hay, and the amount of hay that is fed.