Dark, tarry stool in dogs should always raise a red flag for dog owners. Schedule an appointment with your dog's veterinarian at once. Bringing a fresh stool sample can help the veterinarian during evaluation. Diagnostic tests will be run in order to determine the underlying causes of the dark stool.
Dogs may excrete dark stools at times depending on their diet. However, the presence of dark, black, tarry and foul-smelling stools should be brought to a veterinarian's attention.
Black and tarry stools are often indicative of the presence of digested blood. The presence of digested blood in the stools is known as melena.
Melena mostly occurs when there is bleeding in the stomach or small intestines. It's important to determine where the bleeding is occurring and what's causing the bleeding.
Some of the potential causes of melena in dogs are: bleeding ulcers due to the administration of certain drugs, cancer, the presence of foreign objects, some forms of gastrointestinal disease, metabolic diseases, bleeding disorders, infectious agents, and sometimes the ingestion of blood possibly either from licking a wound or swallowing blood from a mouth injury.
Left untreated and should the bleeding continue over time, the dog may develop anaemia, pale gums, weakness, loss of appetite, weight loss and ultimately death. Melena shouldn't be ignored, as it's often a sign of a serious condition that requires immediate attention.