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Very Dark Diarrhea, Tarry Stool (Melena) in Dogs

Author: Dr. med. vet. Gisa Löwe | Last modified: 17.02.2026

When to visit the vet?

Urgent see a veterinarian within 24 hours

RED in case of weakness/pallor, rapid breathing, collapse, simultaneous vomiting of blood, severe abdominal pain, or if the dog has known coagulation/ulcer risks (e.g., NSAIDs).

Unsure about what’s wrong with your pet? Feel free to use our Symptom Checker for more clarity

Definition

Melena, also known as tarry stool, is a symptom in dogs that occurs when blood from the upper gastrointestinalGastrointestinal refers to the gastrointestinal tract, a system that extends from the oral cavity to the anus and is responsible for the digestion of food and the absorption of nutrients. tract is present in the stool. The stool is typically black and tarry, which indicates the oxidation of blood by stomach acid.

Can Occur with the Following Diseases:

Basics and possible causes

The black color of the stool in melena is caused by bleeding in the upper gastrointestinalGastrointestinal refers to the gastrointestinal tract, a system that extends from the oral cavity to the anus and is responsible for the digestion of food and the absorption of nutrients. tract, which can be attributed to various causes. This bleeding is metabolized through the digestive process, giving the stool a tar-like consistency and color. This can indicate a variety of underlying diseases.

A common cause of melena is a stomach ulcerAn ulcer is an open wound or erosion of the skin or mucous membrane that often heals poorly and can be caused by a variety of factors, including infections and chronic inflammatory conditions., which can be caused by various factors such as stressStress refers to the state of an organism reacting to external stimuli or demands. In veterinary medicine, stress can have physical or psychological effects on animals, impacting their health and well-being., the intake of certain medications (e.g., non-steroidalNon-steroidal refers to medications or substances that are not steroids and often have anti-inflammatory, analgesic, or antipyretic effects. They are used in dogs and cats to treat Pain and Inflammatory conditions. anti-inflammatory drugsAnti-inflammatory drugs are medications that reduce inflammation. They can be divided into nonsteroidal anti-inflammatory drugs (NSAIDs) and corticosteroids and are used in dogs and cats to reduce Inflammatory conditions and Pain.), or infections with Helicobacter pylori bacteriaBacteria are microscopic, single-celled organisms that exist in almost every environment on Earth. Some types of bacteria are beneficial or even essential to life, while others can cause disease.. Tumors in the stomach or small intestineThe intestine is the medical term for the gut, including the small intestine (intestinum tenue) and the large intestine (intestinum crassum). It plays a central role in the digestion and absorption of nutrients. can also cause bleeding that leads to melena.

Other possible causes include severe infections, foreign bodies that injure the gastrointestinalGastrointestinal refers to the gastrointestinal tract, a system that extends from the oral cavity to the anus and is responsible for the digestion of food and the absorption of nutrients. tract, and poisoning that damages the mucous membrane. Systemic diseases such as kidney or liver failure can also affect the lining of the gastrointestinalGastrointestinal refers to the gastrointestinal tract, a system that extends from the oral cavity to the anus and is responsible for the digestion of food and the absorption of nutrients. tract and cause bleeding.

Typical accompanying symptoms

Bloody or black, tarry stool: This is the main symptom and occurs when blood is transported through the digestive tract and takes on the characteristic color.
Vomiting: Dogs with melena may also experience vomiting, especially if the cause is in the upper gastrointestinalGastrointestinal refers to the gastrointestinal tract, a system that extends from the oral cavity to the anus and is responsible for the digestion of food and the absorption of nutrients. tract.
Lethargy: Due to the blood loss, the dog may appear weak and lethargic.
Loss of appetite: Pain or discomfort in the gastrointestinalGastrointestinal refers to the gastrointestinal tract, a system that extends from the oral cavity to the anus and is responsible for the digestion of food and the absorption of nutrients. tract can lead to a decreased appetite.
Pallor of the mucous membranes: A sign of anemia caused by the blood loss.
AbdominalThe term "abdominal" refers to anything that concerns the belly or the abdomen. It is an adjectival expression used to describe the location, symptoms, or conditions that occur in the abdominal area. pain: The dog may react sensitively when the abdomenThe abdomen, also known as the abdominal cavity, is the part of the body located between the rib cage and the pelvis. It houses several important organs, including the stomach, liver, kidneys, intestines, and spleen. is touched or pull it in.
Weight loss: ChronicChronic refers to a condition or disease that is long-lasting or permanent. Chronic diseases often develop slowly and can lead to persistent or recurring health problems over time. bleeding or the underlying disease can lead to unwanted weight loss.

When to see a vet?

A visit to the veterinarian is urgently required if your dog shows symptoms of melena, as this can indicate a potentially life-threatening condition. Particularly alarming symptoms include repeated vomiting, severe weakness, pale mucous membranes, or severe abdominalThe term "abdominal" refers to anything that concerns the belly or the abdomen. It is an adjectival expression used to describe the location, symptoms, or conditions that occur in the abdominal area. pain.

You should see a veterinarian immediately if your dog shows signs of shock in addition to tarry stool, such as rapid breathing, a weak pulse, or a sharp drop in body temperature. These symptoms indicate significant blood loss requiring rapid medical intervention.

Even if the dog is taking medications that could affect the mucous membrane of the gastrointestinalGastrointestinal refers to the gastrointestinal tract, a system that extends from the oral cavity to the anus and is responsible for the digestion of food and the absorption of nutrients. tract, such as anti-inflammatory drugsAnti-inflammatory drugs are medications that reduce inflammation. They can be divided into nonsteroidal anti-inflammatory drugs (NSAIDs) and corticosteroids and are used in dogs and cats to reduce Inflammatory conditions and Pain., the veterinarian should be consulted to review the medication and possibly adjust it.

Symptom recognition for the pet owner and veterinary diagnostic procedure

To detect melena, pet owners should regularly check their dog’s stool for unusual colors or consistencies. A black, tarry color is a clear sign that should not be ignored.

The veterinarian will perform a thorough physical examination to assess the dog’s general condition. Blood tests can help identify signs of anemia or infections. The function of organs such as the liver and kidneys is also checked.

An endoscopyEndoscopy is a diagnostic procedure that uses an endoscope (a thin, flexible tube with a light source and a camera at the end) to examine and visualize the inside of the body, often for diagnostic or therapeutic purposes. may be necessary to visually examine the inside of the gastrointestinalGastrointestinal refers to the gastrointestinal tract, a system that extends from the oral cavity to the anus and is responsible for the digestion of food and the absorption of nutrients. tract and identify possible sources of bleeding. If tumors or ulcers are suspected, a biopsyA biopsy is a medical procedure in which a small amount of tissue is removed from the body to be examined under a microscope for signs of disease. Biopsies can help diagnose cancer and other conditions. may be taken.

Imaging procedures such as X-rayX-ray is an imaging technique that uses X-rays to create images of the inside of the body. It is often used to diagnose bone fractures, lung diseases, and other conditions. or ultrasoundUltrasound refers to sound waves that are above the hearing threshold of the human ear. In medicine, ultrasound is used for diagnostic imaging procedures to visualize internal organs, tissues, and blood flow. can also be helpful in detecting foreign bodies or structural abnormalities in the gastrointestinalGastrointestinal refers to the gastrointestinal tract, a system that extends from the oral cavity to the anus and is responsible for the digestion of food and the absorption of nutrients. tract. In some cases, a computed tomography (CT)Computed tomography (CT) is an imaging technique that uses X-rays and computer technology to create cross-sectional images of the body. It enables a detailed view of bones, organs, and other structures and is used for the diagnosis of injuries, diseases, and for planning medical interventions. scan may also be required.

What the pet owner can do and professional therapy options

Until a veterinarian can be consulted, it is important to keep the dog away from any potentially harmful substances that could worsen the situation. This includes certain medications or foods that could further irritate the gastrointestinalGastrointestinal refers to the gastrointestinal tract, a system that extends from the oral cavity to the anus and is responsible for the digestion of food and the absorption of nutrients. mucosaMucosa, also called mucous membrane, refers to the moist lining of body cavities that are connected to the outside world, such as the mouth, nose, lungs, and gastrointestinal tract. It serves to protect and facilitate the absorption of nutrients..

The dog should be given access to fresh water to avoid dehydrationDehydration occurs when the body loses more fluid than it takes in. This can lead to a number of problems, including headaches, Dizziness, and in extreme cases, renal failure or Cardiovascular collapse.. Solid food should be avoided until a veterinary examination has taken place to avoid putting additional strain on the digestive tract.

The pet owner should make sure to keep the dog as calm as possible in order to avoid unnecessary stressStress refers to the state of an organism reacting to external stimuli or demands. In veterinary medicine, stress can have physical or psychological effects on animals, impacting their health and well-being. and exertion that could worsen the blood loss.

If the dog becomes weak or lethargic, it should be moved to a quiet, comfortable place to rest until it receives veterinary help. In severe cases, the dog should be taken to a veterinary hospital immediately to ensure prompt treatment.

Outlook on current research

Current research on dark, tarry diarrheaDiarrhea refers to the condition of frequent, watery bowel movements, which can be a sign of infections, digestive disorders, or other health problems. in dogs, also known as melena, focuses on the complex mechanisms of gastrointestinalGastrointestinal refers to the gastrointestinal tract, a system that extends from the oral cavity to the anus and is responsible for the digestion of food and the absorption of nutrients. bleeding that cause this symptom. Scientists are investigating the biochemical processes that lead to the discoloration of the stool, particularly the role of hemoglobin in the digestive process. Research shows that melena is caused by the action of stomach acid on blood, leading to a change in stool color. This finding helps veterinarians better assess the severity and location of the bleeding in the digestive tract.

Another focus of research is the development of new diagnostic tools to identify the cause of melena more quickly and precisely. Advances in endoscopyEndoscopy is a diagnostic procedure that uses an endoscope (a thin, flexible tube with a light source and a camera at the end) to examine and visualize the inside of the body, often for diagnostic or therapeutic purposes. and imaging techniques such as magnetic resonance imaging (MRI)Magnetic resonance imaging is an imaging technique that uses strong magnetic fields and radio waves to create detailed images of the inside of the body. It is used in veterinary medicine to diagnose diseases of the brain, spine, and other organs. allow for more detailed visualization of the gastrointestinalGastrointestinal refers to the gastrointestinal tract, a system that extends from the oral cavity to the anus and is responsible for the digestion of food and the absorption of nutrients. tract. These technologies help veterinarians locate lesions, tumors, or ulcers that could lead to gastrointestinalGastrointestinal refers to the gastrointestinal tract, a system that extends from the oral cavity to the anus and is responsible for the digestion of food and the absorption of nutrients. bleeding. The use of contrast agents in imaging is also being researched to improve the visualization of bleeding.

There are also significant advances in research into genetic predispositions for gastrointestinalGastrointestinal refers to the gastrointestinal tract, a system that extends from the oral cavity to the anus and is responsible for the digestion of food and the absorption of nutrients. diseases that can lead to melena. Genetic studies are examining certain breeds that are more prone to gastrointestinalGastrointestinal refers to the gastrointestinal tract, a system that extends from the oral cavity to the anus and is responsible for the digestion of food and the absorption of nutrients. diseases to identify the genetic markers associated with these conditions. In the long term, this research could lead to more targeted treatment approaches and help develop preventive measures that reduce the risk of melena in at-risk dogs.

The role of nutrition in the development and treatment of melena is also being intensively researched. Studies are investigating how certain nutrients or diets can influence the healing of the gastrointestinalGastrointestinal refers to the gastrointestinal tract, a system that extends from the oral cavity to the anus and is responsible for the digestion of food and the absorption of nutrients. mucosaMucosa, also called mucous membrane, refers to the moist lining of body cavities that are connected to the outside world, such as the mouth, nose, lungs, and gastrointestinal tract. It serves to protect and facilitate the absorption of nutrients. and blood coagulationBlood coagulation is a process that helps stop Bleeding when a blood vessel is damaged. Platelets and certain proteins in the plasma form a blood clot that seals the wound.. Researchers are developing special diets aimed at minimizing the strain on the gastrointestinalGastrointestinal refers to the gastrointestinal tract, a system that extends from the oral cavity to the anus and is responsible for the digestion of food and the absorption of nutrients. tract and promoting the health of the intestinalIntestinal refers to the intestine, the part of the digestive tract that extends from the stomach to the anus. Intestinal diseases affect the small and/or large intestine. mucosaMucosa, also called mucous membrane, refers to the moist lining of body cavities that are connected to the outside world, such as the mouth, nose, lungs, and gastrointestinal tract. It serves to protect and facilitate the absorption of nutrients..

Another interesting field of research deals with the microbial composition of the gut in dogs exhibiting melena. Scientists are investigating how the gut microbiome influences digestive health and to what extent dysbiosis—an imbalanceImbalance refers to an imbalance or disruption of normal function or composition in the body, which can lead to health problems. of microorganisms—can contribute to gastrointestinalGastrointestinal refers to the gastrointestinal tract, a system that extends from the oral cavity to the anus and is responsible for the digestion of food and the absorption of nutrients. bleeding. This research could open up new therapeutic approaches using probiotics or prebiotics.

In pharmaceutical research, new drugs and treatment methods are being developed to alleviate the symptoms of melena and treat the underlying causes. This includes advances in the development of medications that reduce stomach acid production, as well as drugs that promote blood coagulationBlood coagulation is a process that helps stop Bleeding when a blood vessel is damaged. Platelets and certain proteins in the plasma form a blood clot that seals the wound.. These new treatments could revolutionize the non-invasive therapyTherapy refers to the treatment of diseases or disorders with the aim of alleviating symptoms, promoting healing, or improving quality of life. Therapies can be medicinal, surgical, or through other medical interventions. of melena and improve the well-being of dogs.

Frequently asked questions

1. What is melena in dogs?

Melena is a symptom characterized by very dark, tarry stool in dogs. It is caused by bleeding in the upper gastrointestinal tract, where the blood is digested and turns the stool black.

2. How do I recognize melena in my dog?

Melena manifests as very dark, almost black stool, which often has a tar-like consistency. Accompanying symptoms can include loss of appetite, vomiting, or lethargic behavior.

3. What causes can melena have?

Melena can be caused by various causes, including ulcers, tumors, medications, infections, or poisonings that lead to bleeding in the upper digestive tract.

4. How is melena diagnosed in dogs?

The diagnosis of melena includes a thorough clinical examination, blood tests, and imaging procedures such as X-ray or ultrasound. An endoscopy may be necessary to identify the exact cause of the bleeding.

5. What treatment options are there for melena?

The treatment of melena depends on the underlying cause. It may include the administration of medication, dietary adjustments, or surgical interventions to stop the bleeding.

6. Is melena in dogs an emergency?

Yes, melena can indicate a serious condition and requires immediate veterinary examination to determine the cause and initiate appropriate treatment measures.

7. Can melena in dogs heal on its own?

Melena itself does not heal on its own, as it is a symptom of an underlying disease. Veterinary treatment is necessary to eliminate the cause and prevent complications.

8. Can my dog's diet affect melena?

Yes, diet can play a role in the treatment and prevention of melena. An easily digestible diet can help protect the gastrointestinal mucosa and promote healing.

9. Are certain dog breeds more susceptible to melena?

Some dog breeds may be more prone to conditions that cause melena, especially those with genetic predispositions for gastrointestinal diseases. Examples include breeds like the German Shepherd or the French Bulldog.

10. How can I prevent melena in my dog?

Prevention of melena includes regular veterinary check-ups, a balanced diet, and avoiding medications or substances that can cause gastrointestinal bleeding. In dogs with known risks, special attention should be paid to signs of digestive problems.