If you noticed blood in a dog's stool, there could be a number of causes. Generally, there are two types of blood present in a dog’s stool – Melena and Hematochezia – and they are the result of different conditions, with different symptoms.

Melena is black or tarry and jelly-like or coffee-ground in appearance. This indicates a problem in the dog's upper gastrointestinal tract (stomach, esophagus, upper small intestine). It may also indicate a problem in the lungs. Melena-blood is darker because it has been digested on its way through the GI tract.

Hematochezia is characterized as being bright red in appearance. This type of bleeding originates in the dog's lower GI, colon, or rectum. This type of blood may be both in the stool or shed after defecating.

How to Tell If a Dog's Dark Stools Contain Blood?

If you cannot see blood in your dog's feces with a naked eye, you can try a few things:

  1. Place dog’s stool on a piece of paper towel.
  2. Check for any abnormalities in the dog's feces (e.g. different shape, consistency, color, size, content).
  3. Notice if there is a reddish residue defusing from the feces. If so, there is most likely melena present.
  4. Obvious bright red blood indicates Hematochezia.

6 Reasons for Melena in a Dog’s Stool

Melena (dark blood) in a dog's stool can indicate serious health issues in your pet, and should be investigated further by a veterinarian.

Blood Clotting Issues

Along with black tarry stools, a blood clotting disorder can also present symptoms such as purple-tinted skin (an indication of blood under the skin). Ingesting rat poison can cause a dog to bleed internally, as well as some diseases like hemophilia.

NSAID Usage Resulting in Ulcers

NSAIDs (Non-Steroidal Anti-Inflammatory drug) such as Aspirin or Rimadyl are blood thinners, and they may cause bleeding ulcers in your dog’s stomach when used long-term. The stools appear tarry because the blood has been digested before elimination.

Cancer or Tumors

Polyps or bleeding tumors can cause melena in dogs, especially those that are aging or are predisposed to certain types of cancers.

Post-Op Complications

If your dog has recently had surgery and you are seeing tarry stools, call your vet immediately. This can be an indication of internal bleeding. Melena can appear up to 72 hours after surgery.

Pepto-Bismol Usage

One of the side effects of Pepto Bismol in dogs is dark stools. However, this medication can also cause gastric bleeding in dogs after long-term usage. Never use Pepto-Bismol long-term unless under the supervision of a veterinarian.

Blood Ingestion

This could be the result of a mouth injury that causes your pooch to swallow blood, or if your dog has licked a gaping wound, which would result in black stools.

6 Reasons for Hematochezia in a Dog’s Stool

Hematochezia (bright blood) in a dog’s stool should also be taken very seriously. One or more of the following issues may be the culprit, but always consult a veterinarian for a full diagnosis.


This serious condition is often found in puppies and is characterized by foul-smelling bloody diarrhea, accompanied by vomiting, loss of appetite, and lethargy. Parvovirus can be fatal and suspected cases need veterinary care immediately.

Dietary Issues

Changes in your dog’s diet or other indiscretions like overeating or the ingestion of foreign objects can all cause hematochezia. If you are changing your pet’s food, do it slowly over a week to avoid inflammation of the colon. Allergies, feeding people food, or the ingestion of spoiled food can also produce bright red blood in your dog’s feces.


Hookworms, whipworms, and roundworms are the most common reason behind hematochezia in a dog’s feces. Protozoa such as coccidia is another internal parasite that may cause blood in the dog’s stool. Bring a fresh sample of feces to the vet, so they can determine if this is the cause.

Hemorrhagic Gastroenteritis

This condition produces large amounts of blood in the stool of a dog, along with other symptoms such as vomiting and diarrhea. Often the cause is unknown, but your dog may need intravenous fluids and medications before the issue subsides.


Dogs that are being held in a shelter, are being boarded, traveling, or have experienced a change in their home-life can develop severe stress which can lead to blood in the stool or a chronic condition called colitis.

Rectal Issues

If your dog swallows a sharp object like a stick or a chicken bone, these can scrap the lower intestine or the rectum as it passes through your dog’s system. If you see bits of foreign material in your dog’s stool, the bleeding should stop once the object has fully passed.

If your dog’s feces is well-formed and has bright red blood on the surface, this could be a sign of rectal polyps. These abnormal growths are highly vascularized and will bleed when the stool passes over them. These types of polyps can be both internal and external.

Injuries to the rectum or the anal glands can also cause hematochezia in dogs.

3 Additional Causes of Blood in Dog’s Stool

Intestinal Blockages

If your dog or puppy has eaten something that cannot easily pass, they could develop an intestinal blockage. This type of condition can also be caused by tumors, inflammation, or a narrowing. Intestinal blockage can be serious, so contact your vet immediately if you suspect this problem in your dog.


Dogs that have experienced trauma or injury may develop bloody stools.


Inflammation in the colon or rectum can cause tearing (fissures) when the animal defecates, which can produce blood in the stool. This condition can be serious and will also need veterinarian attention.


Blood in a dog’s stool should always be taken seriously. Whether it be melena (dark and tarry color) or hematochezia (bright red color), monitor your dog closely for other symptoms, then get to your veterinarian as soon as possible.

READ NEXT: Dog Poop Color Chart – What It All Means

15 Reasons for Blood in Dog-s Stool