Methods of treating adult non-human animals afflicted with diarrhea, particularly, stress-induced diarrhea, by administering to an animal in need thereof an effective amount of a pharmaceutical formulation of a proanthocyanidin polymer composition isolated from a Croton spp. or a Calophyllum spp. are provided. In particular, the adult animals include horses and camels which frequently suffer from stress-induced diarrhea and its symptoms, and the administered proanthocyanidin polymer composition is isolated from a Croton lechleri. The composition, which can be enteric or non-enteric, is administered particularly to target the intestine/gut of the animal via a mode and under conditions conducive and sufficient for providing effective treatment of diarrhea in the affected animal. Preferred modes of administration include orally providing an effective concentration of the proanthocyanidin polymer composition, e.g., via an oral paste formulation, drench, animal feed, or water bottle, to the affected animal.
