You’ve seen the television ads for Pepto-Bismol and Kaopectate. They’re geared to make you grin through your grimaces about that little problem everyone’s embarrassed to talk about–diarrhea. But in horses, diarrhea–particularly persistent diarrhea in adult horses–is no laughing matter, and it’s certainly not something you should keep to yourself. Because of direct consequences such as dehydration and malnutrition, as well as underlying causes such as parasitism and bacterial infections, diarrhea in adult equids can turn deadly.

"Due to the large hindgut (large colon and cecum) in the horse, if they develop an inflammatory condition or a malabsorption syndrome, they can lose tremendous amounts of fluid from the body into the lumen of the intestine and thus out into the feces and out of the body," says Josie Traub-Dargatz, DVM, MS, Dipl. ACVIM, a professor of equine medicine at Colorado State University.

It’s the water content that makes feces loose and soft. By some estimates, a horse with diarrhea can lose as much as 10 gallons (40 liters) of water and salts per day. The resulting dehydration can be fatal, or it can lead to other serious problems, including electrolyte imbalances, weight loss, laminitis, and kidney failure.

In addition, continues Traub-Dargatz, "With certain causes of diarrhea, the causal agent may release or secrete toxins into the intestine, which may be absorbed into the blood, causing toxemia." (Toxemia is blood poisoning caused by toxins–poisons produced by organisms such as bacteria.)

Not every case of diarrhea is cause for high alarm. "It&