Diarrhea is a common problem in horses and can be defined as an increase in frequency, volume, or fluid content of stools. Most of us think of it as loose or watery stools. Diarrhea is not a disease, but a symptom or clinical sign that reflects some change in the digestive tract or in some cases a change in feed. Easiest to understood are the infectious causes, also known as inflammatory or infectious colitis, which includes other signs of inflammation like fever and toxemia. Harder to understand are some of the chronic diarrheas that are not associated with other disease. This article discusses how infectious and noninfectious diarrheas occur in horses and equines. Diagnostic guidelines and rule out lists for most causes of diarrhea in equines are provided, with links to articles about specific causes and treatment of serious diarrhea. Treatment guidelines for acute and chronic diarrhea not associated with serious disease can be found in this article.

They are four reasons your horse's stools can be more watery. Often the history and symptoms will give you a strong clue as to why you have diarrhea which will help lead you to a correct assessment of the cause. When dealing with diarrhea, we tend to differentiate them by how long they are going on and whether there are other signs of disease. Diarrhea of recent and rapid onset, is referred to as acute while those of longer duration or slow development are called chronic. There are four main types of diarrhea:

• Decreased absorption of water from the bowel.
• The bowel looses or actively secretes fluid and other substances into the bowel lumen.
• Osmotically active particles in the digestive tract pull water into the lumen.
• Increased transit time of ingesta due to changes in bowel motility.

Most clinical cases of diarrhea consist of a mixture of these causes of diarrhea with the first step to diagnosing it is to examine the horse and the history.