Small or large bowel diarrhoea: how to tell them apart
5-year-old Labrador with a 2-month history of diarrhoea. The owner describes soft, voluminous faeces two or three times a day, with no straining.
Which finding most strongly supports small bowel diarrhoea?
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A. Tenesmus and abundant mucus in the faeces
These are typical large bowel signs: the inflamed colon produces mucus and rectal irritation causes tenesmus and urgency.
B. Weight loss with increased faecal volume
Correct. The small intestine is the main site of digestion and absorption: its disease produces voluminous faeces, sometimes melaena or steatorrhoea, and weight loss. Frequency rises only slightly and there is no tenesmus.
C. More than five bowel movements a day, each of small volume
Very frequent, small-volume bowel movements are characteristic of colitis: the colon loses its reservoir function.
D. Fresh red blood (haematochezia) on the surface of the faeces
Haematochezia indicates bleeding from the colon, rectum or anus. Blood from the small intestine arrives digested (melaena).
lightbulb Key takeaway
Weight loss is rare in colitis unless disease is severe or diffuse, and it is the most useful clue to small bowel disease. Many cases (especially in cats) are mixed: classifying the diarrhoea guides testing (cobalamin/folate, TLI, ultrasound, upper endoscopy or colonoscopy) but does not replace it.
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.