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Reasons for Blood in a Dog's Stool

Reasons for Blood in a Dog's Stool

Critter Culture Staff



Seeing blood in a pet dog's stools is always alarming. Bloody stools can be a sign of serious illness. However, there are many less serious causes of blood in stools.

Bloody stools may be accompanied by mucus. As they are a symptom of a wide range of canine health conditions, it's important to have the dog assessed by a veterinarian as soon as possible to determine the cause and start any necessary treatment as soon as possible.


What Does Bloody Stool Look Like?

Bloody dog stools can vary in appearance depending on the cause. The stools may contain streaks of bright red blood. There may also be fresh, red blood dripping from the dog’s anus after they have had a bowel movement.

The blood may have a black appearance instead, changing the color of the dog's stools. This indicates that the blood has been digested.

dog stools blood appearance Lukassek / Getty Images


Causes of Bright Red Blood In Dog Stools

Bright red blood in a dog's stool sometimes occurs by chance and doesn't indicate any illness or injury. However, if the stools are consistently bloody or there is a large amount of blood, this is a sign that something is wrong.

This type of bloody stool can indicate an inflammation of the dog's colon called colitis. It could also be caused by parasites, trauma, or ingesting something poisonous. The most serious causes of red blood in stools are parvovirus, a hemorrhage in the gut, and some cancers.

colitis bright red blood dog stool Kameleon007 / Getty Images


Causes of Black Blood In Dog Stools

As some dogs naturally have dark stools, black blood can be difficult to spot. However, stools that are significantly and consistently darker than usual require investigation.

These types of stool could be a sign of problems with the kidneys, liver or pancreas, parasites, trauma, tumors, ulcers, or a reaction to certain medications.

parasites black blood dog stools Raycat / Getty Images


Taking a Stool Sample

It will help a veterinarian to accurately diagnose the cause of blood in a dog's stools if they have a sample to test. It's important that the sample is recent and moist, passed within the last six hours. Place the sample inside a new sealable bag or a stool pot provided by the vet and seal it securely.

However, if the dog appears very unwell or is refusing food and water, it's important to get it to the vet as soon as possible instead of waiting for it to pass a stool to obtain a sample.

stool sample pot dog Zaharia_Bogdan / Getty Images


Accompanying Symptoms

Although blood in dog stools always warrants investigation, if it is accompanied by certain symptoms, then the dog should be seen by a veterinarian urgently. Symptoms to look out for include vomiting, bloody urine, lethargy, breathing problems, and reluctance to eat or drink. These can be signs of a serious health condition.

If a dog starts passing bloody stools after beginning a new course of medication, they could be reacting to it. Stop administering the medication immediately and consult a vet as soon as possible.

dog symptoms blood stools medication jhorrocks / Getty Images


Diagnosing the Cause Of Bloody Stools

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A veterinarian will examine the dog to check for signs of illness. They will also analyze a sample of their stools to look for parasites. Although the parasites themselves aren't usually present in stools, they may contain eggs or spores.

They may also take blood samples to check for other illnesses. An x-ray or scan may be necessary to check for tumors or foreign bodies.



Parvovirus is a very serious cause of bloody stools in dogs and is highly contagious. It's most commonly seen in puppies and also causes vomiting, diarrhea, and loss of appetite. A rare form can cause heart problems. Parvovirus is less common nowadays as dogs are routinely vaccinated against it.

If a dog is unvaccinated and has blood in their stools, it is possible that they have caught parvovirus. It's important to make the veterinarian aware of this possibility before taking the dog in. This will allow them to plan ahead to ensure that the risk of the virus spreading to other dogs is minimized.


Treating Blood In Stools Caused By Parasites

If parasites are found to be the cause of bloody stools, the veterinarian will prescribe de-worming medication to kill the parasites in their system. The dog may also need to go on a special diet for a short period of time.

The vet will also give advice to the owners to help them decontaminate the dog's home environment. This will prevent the dog from becoming reinfected.

worming dog medication parasites pankration / Getty Images


Treating Blood In Stools Caused By Infection

If a viral infection such as parvovirus or a bacterial infection is causing the dog's bloody stools, this can be serious and may require the dog to be hospitalized. The dog may be given intravenous fluids and medications to keep their pain under control and stop them from vomiting. Bacterial infections will require treatment with antibiotics.


Surgical Intervention

A dog with blood in its stools may require surgery if the bleeding is caused by a foreign body blockage. If the foreign body isn't removed surgically, it is likely to be fatal.

Bleeding caused by gastrointestinal cancers or tumors may also require surgical removal. The veterinarian may recommend additional treatment such as chemotherapy.

dog surgery blood stool cancer zoranm / Getty Images


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