Figure 18-1. Normal canine intestinal water balance. Of a total volume of about 3 L of fluid presented to the intestine of a 20-kg dog each day, only about 20% comes from the diet; the remainder comes from the endogenous secretions of the gastroint estinal tract. Most of this fluid is resorbed, and only a fraction of it appears in the feces. A decrease in absorption or, less commonly, an increase in secretion results in an increase in fecal water content and diarrhea.
(From Burrows CF. Chronic diarrhea in the dog. Vet Clin North Am 1983;13:521.)