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Blood in a Dog’s Stool – Causes and What To Do

↯ Key takeaway points

  • Blood in a dog's stool can be a sign of various health issues and should be treated by a veterinarian immediately.
  • There are two types of blood in a dog's stool: hematochezia (fresh blood in the lower gastrointestinal tract) and melena (black, tarry stools from upper gastrointestinal bleeding).
  • Hematochezia can be caused by illnesses such as parvovirus, parasites (including hookworms and Giardia), hemorrhagic gastroenteritis, bleeding disorders, and stomach cancer.
  • Melena can be caused by the use of nonsteroidal anti-inflammatory drugs (NSAIDs), bleeding disorders, and stomach cancer.
  • Treatment options depend on the underlying cause and may include medications, surgery, chemotherapy, or radiation therapy, as well as changes to the dog's diet.
Written by Jay
BsC (Hons) Animal Behaviour & Welfare graduate with a passion for advocating for misunderstood animals.
Zoo and wildlife doctor in veterinary medicine passionate about animal welfare and preventive medicine.
Published on
Friday 28 August 2020
Last updated on
Tuesday 4 July 2023
blood in a dogs stool
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If you see blood in your dog’s stool, it can be a scary experience. However, many causes of blood in a dog’s stool can be treated with veterinary attention. It’s important to take note of your dog’s symptoms to help your vet diagnose their condition.

One critical symptom to note is whether the stool appears as hematochezia or melena. Depending on where the bleeding is coming from, your dog’s stool may show fresh blood or a dark, tarry appearance.

Do not give your dog any antidiarrheal medication, such as Imodium, without first consulting with your veterinarian.

Types of Bloody Dog Stools

Blood in a dog’s stool is categorized as either hematochezia or melena. While both symptoms involve blood in the feces, the origin and appearance of them are very different topics.

Here, we discuss the different types, and what might cause them to occur.


Hematochezia is characterized by the presence of fresh blood in the stool due to bleeding in the lower gastrointestinal tract. The fresh blood may be mixed in with the stool or be expelled by itself. As well as producing bloody stools, your dog might have diarrhea, exhibit a change in bowel habits, exhibit abdominal pains, or even have a fever, depending on the cause of your dog’s hematochezia. In dogs, hematochezia is a symptom of several different illnesses.


Parvovirus (CPV) is a highly contagious virus mainly affecting dogs. Spread through direct and indirect contact, this virus causes mortality in over 91 percent of untreated cases. But why does it cause bloody stool?

The gastrointestinal tract is hit the hardest by CPV. Healthy intestines possess villi, tiny finger-like protrusions that increase the surface area of the intestines. Villi possess their own microvilli, which are readily replaced with new cells, which are produced in the Crypts of Lieberkuhn. Canine parvovirus targets this crypt. Without new cell production, the villi become ineffective and cannot absorb nutrients. More importantly, this breaks down the barrier between the digestive bacteria from the bloodstream. This causes your dog’s diarrhea to become bloody and full of bacteria, causing widespread infection.

If you notice signs of CPV in your pet, take them to the vet right away. Your vet will run an ELISA test to search for virus antigens in your dog’s feces. From here, the rapid implementation of treatment vastly improves your pet’s prognosis. Most dogs receive aggressive fluid therapy, anti-emetic medication, and antibiotics. It’s possible for dogs to contract secondary pneumonia during a parvovirus infection, so your vet may recommend a chest x-ray to rule out this complication.

parvovirus signs in dogs
Beware of any signs of parvovirus.


Various worms can cause bloody diarrhea when they infest in high numbers. Hookworms, for example, attach to the lining of the small intestine, where they ingest blood and rupture blood cells. This causes inflammation in the gut as well as abdominal pain and anemia. In severe cases, blood might be present in the infected dog’s stool. Blood in a dog’s stool may also be caused by other parasites like Giardia. Giardiasis is a parasitic disease caused by Giardia species. This parasite attaches to the intestinal wall of the host and replicates within the gut. This causes the host’s white blood cells to attack injured cells in the gut. As a result, your dog’s intestines become more permeable, causing blood in the stool.

Other parasites that cause hematochezia include:

  • Coccidia
  • Isospora
  • Tritrichomonas fetus
  • Roundworms
  • Whipworms

If you suspect that your pet has intestinal parasites, be sure to contact your vet right away. Your vet will examine a stool sample through fecal flotation. If parasites are noticed, your vet will prescribe an antihelminthic to target any gastrointestinal parasites in your dog. In rare cases, your dog may require a blood transfusion to treat severe anemia.

Hemorrhagic Gastroenteritis

Hemorrhagic gastroenteritis (HGE) is a disease characterized by acute vomiting and bloody diarrhea. Bloody diarrhea often has a foul odor and leads to severe hypovolemia. The intestinal lining becomes more permeable, causing a leakage of blood and proteins into the dog’s bowels. Due to the severity of these symptoms, HGE can be fatal if untreated. Unfortunately, the cause of this disease is currently unknown. Suspected causes include hypersensitivity to food and abnormal responses to bacteria. Plus, for unknown reasons, HGE appears to be more common in small breeds such as Toy Poodles and Miniature Schnauzers.

The clinical signs of HGE are similar to canine parvovirus (CPV) and your vet may carry out a parvovirus test to rule out CPV. Your vet will treat HGE by giving intravenous fluid therapy to replace the lost fluid volume. With treatment, your dog’s prognosis improves massively, so be sure to get your beloved pooch to the vet right away if you have any concerns!


Melena is characterized by black tarry stools, typically as a result of upper gastrointestinal bleeding. If your dog exhibits melena, their stool will be jet back, tar-like, and sticky to the touch. In acute cases, dogs with melena may present with anemia or low blood pressure. But what causes melena?

Use of NSAIDs

Nonsteroidal anti-inflammatory drugs (NSAIDs) are analgesic agents used for controlling your dog’s pain. Your dog might be prescribed with NSAIDs to control conditions such as osteoarthritis, as well as managing pain after surgery. Such NSAIDs include meloxicam (Metacam) and firocoxib (Previcox). But why do these helpful medications cause blood in a dog’s stool?

NSAIDs interfere with mucosal protection in your dog’s gastrointestinal system by reducing how effective the mucus-bicarbonate barrier is. They do this by interfering with how the cyclo-oxygenase (COX) pathways work in your dog’s body. In short, COX-1 regulates key physiological processes such as maintaining the mucus-bicarbonate barrier, submucosal flood flow, and mucosal adaptation to tissue damages. This disruption allows gastric acid to cause damage. Overall, NSAIDs may irritate the stomach lining, causing ulcers and perforations (holes) in the upper digestive tract. This may cause your dog to have tar-like, bloody stools.

If your pet’s prescription medication causes unwanted side effects like melena, be sure to let your vet know. Your pet may need a lower dose of their medication, or to be switched to a different one.

Bleeding Disorders

Bleeding disorders in dogs may be congenital or acquired. Defects in your dog’s blood clotting proteins manifest through delayed bleeding and deep bruises. Platelet defects, on the other hand, show up as small bruises, nosebleeds, prolonged bleeding, and black stools. Acquired thrombocytopenia is common in dogs. Thrombocytopenia due to immune system dysfunction may cause petechiae, bruising, nosebleeds, or bleeding into the bowel resulting in black stools. Similarly, Rickettsial diseases cause severe platelet loss, leading to nosebleeds, bleeding gums, and bleeding into the bowels. This causes melena.

bleeding disorders in dogs
There are multiple reasons for bleeding disorders in dogs.

Some bleeding disorders may be treated with corticosteroids like prednisone. These drugs suppress the clearance of antibody-coated platelets, thus potentially increasing platelet function. They also help to improve blood vessel lining function. Thrombocytopenia treatment involves the removal of potential triggering agents, supportive care, and correction of anemia.

Stomach Cancer

Stomach cancer is cancer that develops in the stomach lining. Early signs of stomach cancer include abdominal pain, nausea, and loss of appetite. As cancer progresses, dogs might exhibit weight loss, difficulty swallowing, and black stools. Unfortunately, many stomach tumors are malignant in dogs. Cancerous tumors often continue to grow and can spread to other organs in the body. Over time, cancerous tumors will interfere with stomach function, thereby increasing the risk of ulceration and obstruction of the stomach. Ulcerating tumors may result in stomach perforations, otherwise known as holes in the stomach. As a result of this perforation, dogs with stomach cancer often present with tarry, black stools.

If you suspect that your dog is suffering from stomach cancer, it’s vital to seek veterinary help right away. Your vet will conduct a full physical examination for your pet. This may include diagnostic imaging, including an X-ray or endoscopy. In addition, your vet may suggest a complete blood count and urinalysis. If stomach cancer is confirmed, treatment may involve surgery, chemotherapy, radiation therapy, or a combination of approaches.

Treatment of Bloody Dog Stools

The first thing to do if your dog has bloody feces is to call your vet. Your vet will ask for details about your pet’s symptoms, so it helps to research the two types of bloody dog stool so that you can explain what your pet is experiencing. This will also help your vet to diagnose your dog’s condition.

Be sure to keep an eye on your pet’s condition whilst you wait for your appointment. If your dog has difficulty breathing, vomits profusely, has a fever, and generally seems extremely unwell, it indicates that your pet has a serious condition that requires immediate veterinary care.

Blood in a Dog’s Stools – FAQ

Need to know anything else about blood in a dog’s stool? Feel free to refer to our Frequently Asked Questions section for more details. If in doubt, always ask your vet for advice.

Is bloody diarrhea in dogs an emergency?

Bloody stool is not a medical emergency unless accompanied by other concerning symptoms. These include vomiting, lethargy, and extreme pain or discomfort. It’s best to call your veterinarian to explain the situation. They’re likely to ask you to schedule an appointment for as soon as possible. As well as this, you may be asked to collect a sample of your pet’s bloody feces for examination.

In preparation for the appointment, it’s best to take some notes that might be relevant. Jot down anything that’s out of character for your dog – rubbing their bottom on the ground, lack of appetite, or signs of being in pain, for example. It’s also important to take note of your dog’s bowel movements too. Is there anything other than blood to take note of? Does your dog strain or seem in pain when going to the toilet? These notes will help your vet to diagnose your dog faster.

If your dog shows other concerning symptoms, be sure to inform your vet right away. Your vet is likely to ask you to bring your pet in as soon as possible. Many conditions involving bloody diarrhea have a better prognosis if treated promptly, such as parvovirus and hemorrhagic gastroenteritis. It’s also dangerous for your pet to have diarrhea for extended periods of time as dehydration can quickly set in.

Why is my dog pooping blood and mucus?

Dog feces often contain mucus. Mucus is a slime-like substance produced in the intestines to lubricate the colon. In healthy dogs, mucus is often the result of shedding dead cells from the lining of the colon, which is a normal process. However, excessive mucus points to a medical condition. If you consistently notice mucus in your dog’s stool, see a lot of mucus, or find it alongside blood, it’s best to make an appointment with your vet.

Like with hematochezia and melena, mucus in the stool indicates conditions such as intestinal parasites, irritable bowel disease, cancer, or colitis. The likelihood that an underlying condition is to blame increases drastically if you find blood in your dog’s stool as well.

How do you treat blood in a dog’s stool?

Treatment of hematochezia and melena is highly dependent on the cause of your dog’s bleeding. This is because several different illnesses can cause blood in a dog’s stool. In order to find out the origin of your pet’s bleeding, your vet will conduct a full physical examination.

If your vet suspects that your dog has intestinal parasites, a fecal flotation test may be done to confirm the diagnosis. Using fecal flotation, the type of parasite can be identified. From here, your vet will treat and prescribe your dog with antihelminthic medication to eradicate the parasites.

Similarly, if your vet suspects that your dog has tumors in their digestive tract, diagnostic imaging may be taken a step further. Your pet will likely be taken for an X-ray, endoscopy, and a complete blood count. Treatment involves surgery, chemotherapy, or radiation therapy. In some cases, other diseases will need to be ruled out first before treatment can continue. For example, hemorrhagic gastroenteritis presents similarly to canine parvovirus (CPV) but treatment is different.

What do you feed a dog with bloody stool?

Depending on the cause of your dog’s bloody stool, your vet might recommend altering your pet’s diet. A change in diet is often recommended in order to manage or lessen your dog’s symptoms.

For example, if your dog is diagnosed with inflammatory bowel disease, a change of diet can help to manage symptoms. The recommended diet is typically hypoallergenic or easily digestible. Similarly, if your dog is diagnosed with stomach cancer, your vet may recommend a different diet for your pet. To combat weight loss due to stomach cancer, the typical diet is high in fat, energy-dense, and low in carbohydrates.

mucus in dog feces
Dog feces contain some amount of mucus.

If you find blood in a dog’s stool, don’t panic. Many conditions are treatable or manageable, and it’s vital that you remain calm and get your dog to the vet right away. Be sure to record your pup’s symptoms, and whether their stool is characteristic of hematochezia or melena.

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