Bright red blood is an obvious cause for alarm. It can be a sign of potentially serious problems affecting the lower part of the gastrointestinal tract or tissues around the anus. Many diseases can lead to bloody stools including constipation, anal gland rupture, intestinal foreign bodies, parvovirus, hemorrhagic gastroenteritis, infections, inflammatory disorders, perianal fistulas, coagulopathies and cancer.
If you notice a small amount of blood in your dog’s stool but it otherwise looks normal and your dog seems to feel fine, a wait-and-see approach is reasonable, but if the bloody stools continue and/or your dog starts to act sick in any way, make an appointment with your veterinarian.
When dogs bleed from the upper gastrointestinal tract or swallow blood, the digestive tract partially digests the blood, making their stools dark and tarry. This is called melena. Melena has many potential causes including gastrointestinal ulcers, foreign bodies, cancer, blood clotting disorders, and respiratory diseases that cause dogs to cough up and/or swallow blood.
Small amounts of digested blood are hard to see in normally brown dog poop. Therefore, if your dog has enough blood in his stool to make it dark and tarry, call your veterinarian as soon as possible.