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Also Known As

Diarrhea, Loose, watery manure


Diarrhea in adult horses can be acute or chronic. Evidenced by an increase in the amount and consistency of manure expelled, diarrhea may develop when the horse eats contaminated, unfamiliar, or inappropriate feed, or may be due to infections caused by bacteria, viruses, or diseases of the colon.

Any horse with diarrhea should be seen by a veterinarian who can detect the source, quickly treat dehydration and electrolyte imbalances, and prescribe remedies.

Chronic diarrhea requires special care because it may be caused by diseases of the intestine, such as cancer, or by deficiencies in the intestinal tract that make it impossible for the horse to absorb nutrients.


  • Loose, watery manure with an increase in frequency of movement and volume
  • Manure that is dark in color, explosive, foul-smelling, bloody, or blood-tinged
  • Loss of weight in chronic cases
  • Listlessness and obvious discomfort
  • In foals, unsightly hair loss around the tail


Diarrhea can develop as a result of a number of factors, including eating contaminated or unfamiliar feed, overeating grain, ingesting sand or dirt, infection by bacteria or viruses, diseases of the colon, poisoning from plants, arsenic or phosphorus poisoning, parasites, and Potomac horse fever. Shipping or transporting the horse, changing the deworming routine, or treatment with certain antibiotics can also cause diarrhea.


The best prevention is the elimination of possible causes of diarrhea from the horse's environment and activities. Isolating horses with diarrhea to prevent spread of the disease and thoroughly cleaning premises and equipment with a formaldehyde disinfectant should help keep the disease in check.


Treatment depends on the cause of the diarrhea. A veterinarian should be called in to do testing and cultures, which might include a fecal examination with special attention to a salmonella culture, testing for Clostridium difficile toxin, a swirl test for sand or the presence of strongyle eggs, peritoneal fluid analysis, and any other tests recommended under the specific circumstances.

Food should be removed, but the horse should be provided with plenty of water. Some veterinarians recommend that horses have access to good quality hay.

If an infectious or parasitic disease situation exists, a veterinarian can assess the situation and help make sure the disease is not passed on to other animals. Any horse that develops severe, acute diarrhea is going to lose weight and the electrolyte balance will need to be maintained.

Inflammatory bowel disease, neoplasia, and parasitism should be ruled out, or treated, depending on findings of the examinations, cultures, and tests. Assessment of body condition is important in determining the main course of treatment.

If salmonella is the cause of the disease, fecal shedding may persist for days to weeks and can pose a risk to other animals or humans. Enteric salmonellosis is characterized by acute colitis and horses may suffer from cardiovascular shock. Fever, abdominal pain, and abdominal distention may be present, as well as other noted symptoms. Ongoing assessment and treatment by a veterinarian is crucial for returning the horse to a condition of good health.

Treatment of chronic diarrhea caused by imbalances in the organisms normally present in the intestines can require time and patience to produce some degree of success. Given a healthy diet and care not to expose the horse to environmental factors that might contribute to diarrhea is important and should reduce the likelihood for future bouts.

In the worst-case scenario, a procedure called transfaunation can be tried. This involves tubing the horse with fluid obtained by straining normal manure or intestinal contents from a horse. This fluid is rich in beneficial intestinal organisms and may help correct imbalances in the affected horse's system.

A diet high in complex fiber (hay, straw, and bran, but no grass) will also aid in obtaining better formed manure and may help with maintaining stability in the horse's intestines and colon. .

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EquiMed Staff

EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.