Bloody Stool in Dogs and Cats

It can be quite alarming to see your pet passing blood in his or her feces, but often the disease is not as bad as the symptom makes it seem.  Blood in dog stool can be in the form of fresh, red blood (haematochezia) or in the form of digested blood (melena).  Melena has a very dark, almost black, and sometimes granular appearance.  Blood in feces is often, but not always, associated with diarrhea. 

One of the most common causes of haematochezia is colitis, or inflammation of the inner lining of the colon.  This can happen secondary to infections of the gastro-intestinal tract, or due to trauma of the lining of the gut.  A common cause of gut lining damage is the ingestion of cooked bones, which can splinter and cause abrasions, or even perforations.  Colitis can often be resolved with antibiotics, and a bland, easily digested diet.
Another cause of haematochezia is the presence of a bleeding mass in the colon or rectum.  These masses can range from benign polyps to more malignant tumours.  If a mass it present, surgical excision, sometimes preceded by a biopsy, may be the logical course of action.

Melena in dogs is an indication of disease higher up in the intestines, such as the stomach or small intestines.  When there is bleeding in this area, the blood becomes digested by the gut on the way down, which gives it it's black, granular appearance and foul odour.  Gastro-enteritis, or inflammation and infection of the gastro-intestinal tract (GIT), is a common cause of melena.  Parvovirus is a severe viral infection of the GIT that occurs most often in young dogs, and one of its symptoms is a very watery melena.  Mild cases of gastroenteritis may be resolved with antibiotics, fasting or resting the gut for 24-48 hours followed by a bland diet.  More severe cases and almost all cases of parvovirus require hospitalisation, IV fluid therapy and injectable medications.
Other causes of melena include the presence of bleeding masses, perforations of the gut and gastric ulcers.  The diagnosis of these requires diagnostic imaging and other tests and treatment will depend on the cause.

Fresh or digested blood in the feces warrants a visit to the vet as at the very least, a physical examination and antibiotics would be required.

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