Blood in a dog’s stools can appear in several ways, each indicating a different problem.
- Black stools mean bleeding high up in the digestive tract, most likely a bleeding stomach ulcer.
- Reddish stools indicate blood further down the pipe, after the digestive juices have been neutralized somewhat. This can be anything from ulcers in the small intestine to ulcerative colitis.
- Red blotches/streaks on the surface of the stools (with normal color otherwise) indicate bleeding in the last segment of the large intestine or rectum, after the stool has begun to solidify (the function of the large intestine is to neutralize digestive juices and absorb liquid). This can be ulcerative colitis (or some other inflammatory bowel disease) or bleeding hemorrhoids.
Each of these problems can be very serious, and in some cases life-threatening (with the exception of hemorrhoids).
Coloring (natural or artificial) in food can also directly color the stool so you can’t be sure of anything without a chemical analysis. A sudden diet change/addition can also affect stool color.
Get a sample to the veterinarian.