Fecal Assessment

Why Distinguish Between Small and Large Bowel Diarrhea

Examination of defecation frequency, fecal characteristics and fecal scoring as well as patient history can be used to determine if a pet’s diarrhea originates from the small intestine versus the large intestine ꟷ or if both segments of the gastrointestinal (GI) tract are affected. A diarrhea localization assessment can help narrow the list of possible causes, help determine a plan of action, and provide a baseline for assessing improvement.

Key Messages

• Initial localization of diarrhea into “small bowel” versus “large bowel” can help focus the physical examination, prioritize differential diagnoses, guide diagnostic test selection and clarify underlying causes. 
• Although diarrhea associated with some GI disorders appears related to either the small or large bowel, in many cases the disease process involves both small and large intestines. Diarrhea of “mixed bowel” origin has some characteristics of both small and large bowel diarrhea. 
• In addition to appropriate medical management, dietary management may aid in patient care. Identifying diarrhea as small or large bowel in nature can help guide selection of an appropriate diet. 
  • Dogs with small bowel diarrhea may benefit from a highly digestible diet that has low to moderate fat content. If food allergy or intolerance is suspected, an elimination diet containing a novel or hydrolyzed protein may be appropriate. 
  • Dogs with large bowel diarrhea may benefit from a diet containing an increased level of dietary fiber. A blend of soluble and insoluble fibers helps promote intestinal motility and support GI health. If food allergy or intolerance is suspected, an elimination diet containing a novel or hydrolyzed protein may be appropriate. 
  • Cats with small bowel diarrhea may benefit from a highly digestible, moderate-fat intestinal diet that is lower in carbohydrates. If food allergy or intolerance is suspected, an elimination diet containing a novel or hydrolyzed protein may be appropriate. 
  • Cats with large bowel diarrhea may respond to a hydrolyzed or novel protein elimination diet that decreases antigenic stimulation of the GI tract. Other cats may benefit from a fiber-enhanced food that includes both soluble and insoluble fiber. 
• Specific probiotic products can be administered to help manage small, large and mixed bowel diarrhea of cats and dogs. Since not all probiotics are equal or interchangeable, it is important to choose one that has been clinically tested and formulated to deliver the desired effect (e.g., help manage diarrhea).

Marks, S. L. (2013). Diarrhea. In R. J. Washabau & M. J. Day (Eds.), Canine & feline gastroenterology (pp. 99─108). Elsevier. 

Zoran, D. L. (2017). Nutritional management of gastrointestinal disease. In S. J. Ettinger, E. C. Feldman & E. Côté (Eds.), Textbook of veterinary internal medicine: Diseases of the dog and the cat (8th ed., pp. 1892─1899). Elsevier.