What this means
Normal dog stool comes in many shades of brown, and a darker shade does not by itself mean blood. Stool that truly contains digested blood is usually genuinely black, shiny and sticky, like a smear of tar, and has a very sharp, unpleasant smell. If you are unsure, you can smear a little on a white paper towel, where real blood shows as a reddish brown rather than just a dark streak.
Something your dog ate can also darken the stool, so the vet will ask what your dog has eaten over the last two or three days and whether it has had any medicines or additives. Write down everything you remember, and say if your dog may have found something on a walk.
Also note whether your dog is vomiting, whether it is active, whether the gums are a healthy colour and whether there are other signs of bleeding. These details help tell a minor digestive upset from something more serious.
Possible causes
These are things that can cause this sign. It is not a diagnosis, and they are not equally likely for your dog.
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Bleeding in the upper digestive tract
Damage to the stomach or small bowel lining can bleed, and the blood turns black along the way. Your dog may also vomit or become dull.
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Long-standing bowel inflammation
Inflammation of the bowel that goes on for a long time can show as recurring diarrhoea, weight loss and sometimes blood in the stool.
About the condition: Inflammatory bowel disease (IBD) -
A blood clotting disorder
Some disorders make the blood clot less well, so bleeding can occur in several places. There may be nosebleeds, bruises or blood in the urine.
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A growth in the digestive tract
Occasionally a growth in the stomach or bowel bleeds. This tends to show slowly, with a dog that gradually eats less, loses weight and tires sooner.
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Something eaten that darkens the stool
Some foods, medicines or swallowed objects turn the stool dark. Only a vet can judge whether this is harmless.
What else to watch for
These observations help your vet build the picture faster. Note down what you saw and when.
- Whether the stool is truly black, sticky and tar-like, or just dark brown
- Whether the smell is unusually sharp
- How many days it has lasted
- Whether your dog is vomiting, and whether it eats and drinks as usual
- Whether the gums are pink or pale
- Whether there are bruises, nosebleeds or blood in the urine
- What your dog has eaten and any medicines it has had
When to book a routine visit
If the stool is black or tar-like more than once, contact a vet the same day or the next, even if your dog seems well. Bring a photo or sample of the stool and say what your dog has eaten and whether it has had any medicines.
Related conditions
Conditions whose entries mention this sign. The list is somewhere to read on, not a way to reach a diagnosis.
- Inflammatory bowel disease (IBD) Digestion and liver This is a long-term disorder of the digestive tract in which inflammatory cells build up in the wall of the stomach or intestine, so it becomes less able to digest food and absorb nutrients. The exact cause is not fully understood; an interplay between the immune system, gut bacteria and food is thought to play a part. Because many other digestive problems look much the same, a vet works out what is really going on with tests.
- Thrombocytopathy Blood and immunity Thrombocytopathy is a blood clotting disorder in which the blood has enough platelets but they do not work as they should, so bleeding is slow to stop. It can be inherited or arise from another illness or certain drugs. In such a dog even a small wound or a veterinary procedure can lead to prolonged bleeding, so it is worth telling the vet about it beforehand.
- Von Willebrand disease Blood and immunity Von Willebrand disease is an inherited bleeding disorder in which the body lacks a protein that helps platelets stick together and plug a damaged blood vessel, or the protein doesn't work properly. As a result even a small wound can bleed for longer than normal, and the disease varies in severity, sometimes only coming to light after an injury or a procedure. Genetic tests exist for some forms.
- Cancer Cancer Cancer is not one disease but a whole group of different malignant tumours that can appear in almost any organ or tissue. They can grow slowly or quickly and spread to other parts of the body, so the earlier a change is noticed, the more options a vet has. Only a vet can tell whether a lump or other change is malignant.
Body systems: Digestion and liver Blood and immunity Cancer