Diarrhea in Horses

What Is Diarrhea in Horses?

Diarrhea in horses can occur at any age and for a variety of reasons. Depending on the severity of the diarrhea, it can quickly lead to a medical emergency as horses become dehydrated from a loss of fluid.

If your horse starts having diarrhea, it is very important to call your veterinarian right away and to isolate the horse from other horses in case the cause is infectious. Allowing the horse access to fresh, clean water is also very important to help reduce the risk of dehydration.  

Symptoms of Diarrhea in Horses

Horses experiencing diarrhea may exhibit the following symptoms: 

• Loose/watery stool 

• Acting painful or colicky

• Lethargic  

• Anorexia (not eating) 

Causes of Diarrhea in Horses

Diarrhea may be caused by these several different factors: 

• Infectious agents (clostridium, Salmonella, coronavirus, Potomac horse fever) 

• Parasites  

• Sand ingestion 

• Stress 

• Gastric/stomach ulcers 

• Changes in diet 

• Non-steroidal, anti-inflammatory drug administration 

• Inflammatory bowel disease 

• Toxins 

• Neoplasia 

How Veterinarians Diagnose Diarrhea in Horses

Veterinarians diagnose diarrhea in horses based on its medical history, physical exam findings and diagnostic testing.  

To obtain a thorough history, the veterinarian may ask questions about changes in your horse’s diet or lifestyle, as well as any recent travel or exposure to new horses. They may also want to know about the horse's vaccine and deworming history.  

During a physical exam, the veterinarian looks for signs of dehydration (dry and tacky gums/mucous membranes, visual skin tent, sunken eyes), and listens to its heart, lungs and abdominal gut sounds for abnormalities such as hypermotility (increased gut activity). They will also want to take the horse's temperature for signs of a fever which may indicate an infectious cause of diarrhea. 

Fecal samples may be taken to test for parasitic egg count and bacterial culture. A fecal sample can also be used to look for sand in the feces.  

If there is a concern that your horse could have a systemic (body-wide infection or disease) condition causing the diarrhea, your vet may want to do further diagnostic testing such as blood work including a complete blood count and chemistry to look at its internal organ function.  

Ultrasound and radiographs (X-rays) may also be advised to look at the intestines for any abnormalities such as thickening. Radiographs are a great way to find abnormalities (such as sand) that has accumulated in the intestines.  

If the suspected cause of diarrhea is due to gastric ulcers and/or stress, the veterinarian will likely want to perform an endoscopic exam in which a scope is guided down the horse's nose into the esophagus and stomach to examine any visual ulcerations. This test must be done after fasting and is generally performed at a veterinary clinic or hospital.   

Treatment of Diarrhea in Horses

Treatment depends on the underlying cause of the diarrhea, the age of the horse, and the severity of the symptoms.

In mild cases, treatment may include gastrointestinal support with probiotics or a gastrointestinal supplement and monitoring. Most adult horses that develop diarrhea—with no other symptoms—will be back to normal in a day or two. In more severe cases, your horse may need intravenous (IV) fluids, electrolytes anti-inflammatories, and antibiotics. 

Treatment of Diarrhea Caused by Infectious Disease 

Infectious causes of diarrhea include clostridium, Salmonella, coronavirus, and Potomac horse fever. These conditions will likely lead to a severe disease with dehydration, fever, and a very sick horse that requires veterinary care immediately. A large percentage of these horses require hospitalization with intravenous fluids and electrolytes due to severe dehydration. They should be isolated from all other horses as these types of infections are extremely contagious.  

Treatment of Diarrhea Caused by Parasites 

Diarrhea caused by parasitic infection is common and requires a fecal exam to determine the type of worm present. Once known, the veterinarian will discuss with you the best deworming protocol for treatment and future prevention. Fecal testing can often be performed at your local veterinary clinic or sent off to the veterinarian’s lab of choice for testing.

The worms that can infect horses and cause diarrhea include: 

• Small redworms (Cyathastomes) 

• Large redworms (Strongyles) 

• Ascarids 

• Intestinal threadworms (Strongyloides Westeri) 

• Tapeworms 

• Bots 

• Lungworms 

Based on the fecal results, your veterinarian can decide on the best deworming medication and protocol that is most beneficial. Your veterinarian may also recommend starting your horse on a gastrointestinal supplement or probiotic to help support the gut as it heals from the worm infestation.  

Treatment of Diarrhea Caused by Sand Accumulation 

Treatment of diarrhea caused by sand accumulation in the intestinal tract will likely include feeding a product such as SandClear® to help the sand to pass over time. The veterinarian will likely want to perform follow-up exams to make sure the sand is dissipating with the prescribed supplementation. If the horse lives in a sandy environment, new management may need to be implemented to prevent the horse from ingesting sand in the future. 

Treatment of Diarrhea Caused by Stress and Gastric Ulcers 

Horses that are stressed are much more likely to develop gastric ulcers. Treatment of stress and ulcers often includes changing the horse’s lifestyle to include more time to graze in a pasture or other turnout methods. Some horses may also benefit from having a friend turned out with them or toys to play with. 

Other management changes may include a reduction in the amount of grain fed, an increase in forage given, and the reduction of the time a horse goes without forage.  

The veterinarian may also prescribe Gastrogard®, a medication to help ulcers heal. If your horse is prone to stress, the veterinarian may prescribe Ulcergard® or Gastrogard as a preventative measure for ulcers in times of stress, like travel.  

Treatment of Diarrhea Caused by Change in Diet 

Diarrhea from a recent change in diet is usually does not require any veterinary care. Slow transitions to any new food, or forage over 7-14 days, is best for the prevention of diarrhea and appetite changes. 

Treatment of Diarrhea Caused by Medication 

If a horse develops diarrhea while on any type of non-steroidal anti-inflammatory (NSAID) medication such as Banamine® (flunixin meglumine) or Bute® (phenylbutazone), call your veterinarian immediately before giving it the next dose. Some horses can develop right dorsal colitis due to administration of NSAIDs. This can be severe and require veterinary care.  

Treatment for Other Causes of Diarrhea in Horses 

Other less common reasons that horses may develop diarrhea include toxin ingestion, neoplasia/cancer or inflammatory bowel disease (IBD). Treatment for toxin ingestion will depend on the toxin ingested and other symptoms, but supportive care will likely be implemented by the veterinarian. Neoplasia may be very hard to diagnose and treat and will also commonly include supportive care. Horses that have chronic episodes of diarrhea may be diagnosed with inflammatory bowel disease and require a special diet, gastrointestinal supplementation and veterinary care to try to reduce the symptoms. 

Recovery and Management of Diarrhea in Horses

Recovery and management of diarrhea depends on the initial cause and severity. In general, horses will recover faster the earlier diarrhea is observed, and medical intervention is started.  

Infectious and parasitic agents cause the greatest potential for serious dehydration, and the risk of developing severe infections leading to endotoxemia and colic. Endotoxemia occurs when bacteria in the intestinal tract die, and toxins are released into the intestines and travel to the bloodstream. Endotoxemia is a life-threatening condition in horses. 

Prevention of Diarrhea in Horses 

Always provide horses with good, quality forage and gradually introduce any changes in diet. Discuss your farm’s fecal egg count and deworming protocol with your primary vet. Monitor your horse's stress level—especially when traveling and competing. Horses that do seem to easily develop diarrhea may do well on a probiotic or GI support supplement such as AssureGuard Gold made by Arenus, or digestive supplements made by KER or Platinum Performance. These can help restore the normal gut flora and help to maintain good gut health.