Diarrhea can affect horses of all ages, breeds and sizes, resulting in dehydration, weight loss, poor nutrient absorption or electrolyte imbalance.

Diarrhea is described as the increased excretion of liquid or semi-solid feces. Cases of equine diarrhea can range in severity from mild episodes to serious and long-term episodes, which may require veterinary attention.

Diarrhea itself is not a disease, but a symptom of another underlying condition. Unfortunately, the underlying cause is not identified in 50% of equine diarrhea cases. [1][2][3]

An imbalance of the gut microflora (known as dysbiosis), is a cause or result of many types of diarrhea in horses. This can be caused by dietary factors, although there are many reasons why a horse may have dysbiosis and diarrhea. [4]

This article describes the common causes of diarrhea, the complications associated with this condition, as well as methods to treat and manage non-infectious diarrhea in horses.

Common Causes of Diarrhea

Diarrhea in horses may arise from many possible causes, both non-infectious and infectious in nature. [1][5][6][7]

Non-infectious causes include, but are not limited to:

Infectious causes of diarrhea in horses may include:

  • Bacterial infection:
    • Salmonella
    • Clostridium difficile
    • Clostridium perfringens
    • Potomac horse fever
    • Aeromonas species
    • Lawsonia intracellularis in young horses
  • Viral infection:
  • Parasitic infection:
    • Larval cyathostomiasis
    • Strongyloides in foals
  • Protozoal infection:
    • Cryptosporidium parvum primarily in foals
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Non-infectious Causes of Diarrhea

There are many proposed non-infectious causes for diarrhea in horses. Ultimately, anything that interferes with fluid and sodium absorption, pulls fluid into the gut, alters motility or shifts the microbial population in the gut can predispose your horse to diarrhea.

Commonly described risk factors which may be influenced by management practice are listed below:

Carbohydrate Overload:

When diarrhea is observed in a horse, diet is often suspected as the most likely cause. [4]

The physiology of the equine gastrointestinal tract is specialized to the fermentation of fibre in the hindgut, composed of the cecum and colon.

Microbes in the horse’s hindgut ferment fibre in forages to produces volatile fatty acids (VFAs), which serve as a valuable energy source for the horse.

Additionally, the small intestine of the horse is limited in its capacity to digest starch from carbohydrate-rich meals. It contains limited quantities of the enzyme that breaks down starch (alpha-amylase). [8][9]<