What Causes a Horse to Have Diarrhea

When a horse experiences an increase in the volume of feces, has more fluid content to their stools, or has more frequent bowel movements than normal, then it is highly likely that they have diarrhea. Diarrhea in horses can be either acute, happening suddenly, or it can be chronic.
Whenever acute diarrhea is experienced by a horse, it should be treated as a medical emergency. When diarrhea continues for 14 days or more, it shifts to being chronic diarrhea.

There are many reasons why a horse could have diarrhea. A veterinarian will run a series of tests, including blood work and a physical examination, to determine what the cause may be. There will be several fecal examinations performed as well to determine causation. Additional tests, such as an ultrasound, rectal palpation, and belly tapping may also be necessary.

In some instances, an intestinal biopsy or an absorption test may be required to diagnose the cause behind the diarrhea.

Always consult with a veterinarian regarding this health issue and do not rely on guides such as this to produce an outcome. This information is not intended to serve as a substitute for a treatment plan or be used as a diagnostic tool.

Here are some of the causes of diarrhea in horses that are common.

#1. Bacterial Infections

There are multiple types of bacterial infections that can affect horse health and be the cause of diarrhea. Two of the most common types of infections that horses experience are salmonella infections and Potomoc horse fever, or PHF.

PHF is a form of equine colitis and the infections lies within the intestinal tract of the horse. Cases may be mild, but severe cases can be life-threatening. It is most commonly seen along the U.S. East Coast, but may occur anywhere in the world. The initial fever with PHF is often missed, but a second fever can occur and trigger swelling in the limbs, increased toxin rates, and even laminitis. 

Salomnella infections are often found in the food of the horse and can be spread through fecal contact. What makes this infection so dangerous is the fact that a horse may exhibit no signs of infection until it becomes quite severe. Look for twitching, straining, and dehydration with the horse. Some horses with a mild infection may exhibit a lack of appetite.

More than 100 different bacterial infections in horses have been identified that can cause diarrhea. For that reason, a veterinarian exam is often required. 

#2. Intestinal Parasites

Intestinal parasites are very common with horses. Egg counts on fecal matter should be performed on a regular basis to ensure good health. A count at least twice per year, and sometimes once per quarter, may be necessary.

The three most common types of parasites that affect horses are roundworms, strongyles, and tapeworms. Many parasites are quite small, but some may grow several inches in length. What can make them difficult to detect is that the larvae can survive for more than 6 months in non-optimal environmental conditions. 

Pasture management techniques and medication tend to be the treatment methods. Some treatments may require a stomach tube to be effective.

#3. Changes in Food

Any change to the feed of a horse offers the chance for diarrhea to occur. Avoid rapid changes in feed, when it becomes necessary to make a change, to limit the risk of this health issue forming.

Diarrhea tends to occur most frequently when a horse is first introduced to a new and lush pasture. Limit the time a horse can spend in a lush pasture at first to decrease the risks of diarrhea. Grains and concentrates should be kept at a minimum during a feed change cycle as well. 

#4. Antibiotics

When a bacterial infection occurs, a veterinarian may prescribe antibiotics to help the horse recover. Although the medication will eliminate the infection, it may also change the balance of the helpful gut bacteria as well. When the gut bacteria are imbalanced, there is a good chance that diarrhea will form.

The only way to treat this condition is to restore the balance of helpful gut bacteria. That can be difficult to do if the horse is on a long-term antibiotic therapy. You will need to speak with your veterinarian about this issue because the treatment plan must be designed with the individual horse’s symptoms in mind.

Diarrhea caused by antibiotics can also resolve on its own after a couple of days. You may be asked by your veterinarian to wait out the symptoms. 

#5. Sand Consumption

Because horses are pasture animals, there is always the chance that they could eat soil, dirt, and sand as they munch on some grass, alfalfa, or hay. Some horses will purposely eat sand because they’re bored. In some cases, horses attempt to eat sand because they are suffering from a mineral deficiency.

The most common time to see sand consumption in horses is during the time when they shed their winter coat.

To stop sand consumption, the cause of the behavior must be identified. If it is a learned behavior that occurs because of boredom, stall toys and more personal attention can prevent further cases of diarrhea. Introducing the horse to a herd if it is on its own, even if it occurs only once or twice per month, can help to alleviate loneliness and boredom as well.

If there is a mineral deficiency, then add a mineral lick or change the supplements and grains being given to the horse.

#6. Inflammatory Bowel Disease

IBD occurs in horses when the immune system of the animal begins to attack the digestive system. It may also occur because of an allergy to a product in the horse’s feed, the presence of an ulcer, or have an unknown cause.

Treating IBD often requires a change to the feed of the horse. Some horses may require a complete pelleted diet, such as hay pellets, to avoid diarrhea and colic. Increased proteins, added beet pulp, and fat supplements may also be recommended, depending upon the classification of IBD that is diagnosed.

Some horses with IBD may even benefit from being fed a gluten-free diet.

Because inflammation is involved with this disease, some horses may be prescribed anti-inflammatory medication to help deal with their diarrhea. Adding additional fiber to the diet of the horse may be helpful in some instances as well. If IBD is the diagnosis, it becomes a lifelong management of the horse’s diet to prevent diarrhea from returning. 

#7. Heart or Liver Changes

Heart disease and liver disease can dramatically alter the quality of life a horse experiences. The onset of symptoms from these organ changes can be abrupt, especially since 75% of the liver must be affected before a horse will show any clinical signs of this issue.

Horses dealing with liver and heart changes may also experience weight loss, increased instances of colic, and chronic fever. Circling, aimless walking, and head pressing are common behaviors seen when dealing with this type of health issue.

Depending upon the cause of the disease or organ changes, surgery may be able to repair the damage that is caused. Certain medications may be prescribed to slow down the disease or changes that are occurring. In some instances, unfortunately, there may also be nothing that can be done to help the horse and palliative care may be the recommendation. 

#8. Cancer

Cancer can be tricky to spot in horses, especially if it is not a skin tumor. Cancer is relatively rare in horses, but acute diarrhea can be a symptom of it.

If all other attempts at diagnosing the diarrhea have failed, a veterinarian may work up a series of tests to determine if there are markers that indicate the presence of cancer. Lymphoma tends to be the most common cancer, by carcinomas, sarcoids, and other cancers are possible as well. 

Treating cancer often means using chemotherapy and immunotherapy, but the treatments can be quite expensive. Many horses are not diagnosed with cancer until it is at an advanced stage, which further complicates the diagnosis. 

There are also times when a horse may have diarrhea and the cause may never be discovered.

By treating diarrhea immediately through a treatment plan that is developed by a veterinarian, it is often possible to stop diarrhea quickly so the horse can return to good health. This is especially true if the cause of the diarrhea can be eliminated. 

Part of a treatment plan will often involve giving a horse prebiotics and probiotics. Yeast supplements may be recommended, along with amino acid supplements. The horse may be required to have changes to their diet if the grain or hay they are consuming is believed to be the cause of the diarrhea.

When diarrhea is seen in horses, there is the possibility that it could be contagious to other members of the herd. Take action right away to protect each horse so that an acute case of diarrhea doesn’t necessarily need to turn into a chronic case.