Diarrhea in Horses

Diarrhea is not in itself a disease, but instead a symptom of many diseases, recognized when a horse’s feces change in consistency from the normal firm, well-formed fecal balls to runny, liquid feces. Diarrhea can range from merely loose stools to completely watery in appearance. There are certain instances in which a bit of diarrhea is normal, such as a sudden change of environment or feed, however, long bouts — those that persist more than a few days — or severe forms of diarrhea is not normal and require veterinary assistance.

Symptoms and Types

There are many causes and types of diarrhea leading to a range of severity. Mild diarrhea may go unnoticed for long periods of time if the horse is always out at pasture. As the severity of diarrhea increases, you may see fecal staining underneath the horse’s tail. In general terms, diarrhea can be classified as acute or chronic. Other than the obvious change in fecal consistency, you may see the following clinical signs:

Acute diarrhea:

¨       Fever

¨       Lethargy

¨       Inappetance

¨       Loud gut sounds

¨       Dehydration

¨       Signs of colic (abdominal pain)

¨       Weakness

¨       Edema (fluid accumulation in lower limbs and underneath the abdomen)

Chronic diarrhea:

¨       Weight loss

¨       Poor, unkempt appearance such as dull eyes and rough hair coat

¨       Lethargy


As previously stated, diarrhea is a common symptom for many different diseases. Listed below are a few causes to some of the more common forms of diarrhea in horses.

  • Chronic Diarrhea
    • Parasites
    • Excessive ingestion of sand
    • Chronic Salmonella infection
    • Inflammatory or infiltrative bowel disease
    • Neoplasia (lymphosarcoma in the gut)
  • Acute Diarrhea
    • Salmonella infection
    • Clostridial infection
    • Potomac Horse Fever
    • Antibiotic-associated diarrhea
    • NSAID (Non-steroidal anti-inflammatory) toxicity
    • Assorted toxicities (i.e. arsenic, cantharidin, various plant toxicities)


Finding the cause of the diarrhea can be a challenge and does require the intervention of a veterinarian if the horse is systemically sick or the diarrhea has been persistent.

Your veterinarian will first perform a thorough physical exam on your horse, taking note of any dehydration or other problems secondary to the diarrhea that will need immediate attention. Your veterinarian will then likely take a blood sample as well as one or more fecal samples. Depending on the clinical signs the horse is exhibiting, the vet may test the feces for parasites, or may submit the sample to a diagnostic lab to test for bacteria such as Salmonella and Clostridia. If the diarrhea has been chronic and inflammatory bowel disease is suspected, sometimes an abdominal ultrasound is recommended, or even an intestinal biopsy.


The name for the species of horses, donkeys, mules


A medical condition in which the body has lost fluid or water in excessive amounts


Usually used in veterinary medicine to refer to certain drugs that are designed to combat intestinal worms in animals.


Term used to imply that a situation or condition is more severe than usual; also used to refer to a disease having run a short course or come on suddenly.


The process of removing tissue to examine it, usually for medical reasons.

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