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

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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 horses’ 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 when its upset, diarrhea is frequently the result. But what are the causes the disruption, 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 its 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 their body of critical moisture needed for their 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 is dormant and will remain that 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, which prevents the absorption of fluids. 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 or Banamine. And antibiotics are essential in treating our equine friends, but they often are a cause of diarrhea.

Antibiotic-associated diarrhea (AAD) not only causes a horse to feel bad, but it can also be fatal. It’s believed equine antibiotics decrease principle 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 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, lay eggs passed in the horse’s manure.

Diagnosing the cause

It’s essential to determine the cause of diarrhea so you can treat it effectively. Sand induced intestinal inflammation reacts well to treatment; however, some cases need aggressive treatment if your horse has any chance to recover.

Physical exam

Picture of a vet checking a horse that has diarrhea,

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

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 is chronic weight loss 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.

To find out if your horse is dehydrated, perform a simple skin tent test. 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.

If they are pale or white, your horse doesn’t have enough fluid. 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.

Treating diarrhea

Treatment varies based on the cause of the sickness and 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. It is at risk, and you don’t want your horse to dehydrate and colic!

Diarrhea can be fatal, so don’t take any chances.

Preventive measures

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

In reality, diarrhea is inescapable, but there are some steps you can take to reduce the risk that your horse develops the problem.

  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


If your horse has diarrhea, it needs to be attended to right away. Hopefully, its 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 persist for more than 24 hours. If you’re unsure, don’t take any chances; call the vet.

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