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What are Some Causes of Blood in the Stool of Animals?

By Sheri Cyprus
Updated Jun 04, 2024
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Bright red blood in the stools in animals is called hematochezia and it signifies lower intestinal tract bleeding. Black, tarry blood is called melena and it signifies upper intestinal tract bleeding. Blood in the stools is often caused by internal parasites, allergies, bleeding ulcers, ingested blood or gastrointestinal diseases.

Internal parasites cause blood in the stools in animals due to the irritation the parasites create in the digestive tract. Hookworms survive on the blood in the small intestine and often cause anemia which can often be noticed by pale gums as well as black blood in the stools. Puppies are especially susceptible to serious harm or death from hookworms.

Whipworm infestations affect the colon and can cause bright red stools. It is quite rare in cats, but fairly common in dogs. Whipworms look like long whips and the eggs can be seen in a fecal exam. By the time the blood appears, there is likely to be a large number of the parasites in the animal's colon.

Bright red blood in the stools may also be caused by food allergies. An allergic reaction may be likely if blood is accompanied by other allergy symptoms in animals such as constipation or diarrhea, ear infections, rashes or skin infections. Itchiness is another symptom of allergies in animals.

Bleeding ulcers in the stomach or the esophagus causes black blood in the stools in animals. Bleeding ulcers are also called peptic ulcers. An ulcer is an open sore caused by an irritant such as an acid, drug or bacterium. Ingested blood, such as from killing and eating prey, is another cause of black stools.

Gastrointestinal diseases also cause blood to appear in the stools. Black blood is often associated with lymphoma. Lymphoma is a cancerous condition of the white blood cells and is fairly common in dogs. Inflammatory Bowel Disease (IBD)is fairly common in cats. Blood in the stools in animals with IBD is sometimes the only symptom of the disease. The blood occurs as the cells in the digestive tract become inflamed.

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Discussion Comments
By rallenwriter — On Oct 11, 2010

About once every few months my dog has a bleeding bowel movement, and I'm really desperate to know what could be going on.

I've had him tested for all kinds of worms, and nothing has come back positive, and they say he doesn't have cancer.

He's an inside dog, so he doesn't eat anything bloody, and I don't think he has an ulcer or anything.

What could be some other causes of intermittent bloody stools in dogs?

I'm really worried about him, and I've tried changing his diet a few times, so I'm really running out of options.

What should I do?

By Planch — On Oct 11, 2010

What would be some of the causes of bloody stools in an inside cat who only eats store-bought food? She has been an inside cat for as long as I've had her, but recently she's started having bleeding bowel movements.

I'm just afraid that it's one of the more serious bloody stool causes, since she's getting older, and has also been throwing up more often than usual.

What do you think?

By TunaLine — On Oct 11, 2010

My dog has never had blood in his stool before, but last night he got out (he's usually an inside dog), and was out all night in the woods around our house.

This morning he's had several dark, tarry stools, and I was really wondering what could be causing him to have so many stools with blood.

I was thinking that since it happened so suddenly, that he might have just had a crazy night and eaten a lot of animals or something last night, and the blood from the animals might be causing the weird stools.

He hasn't had any other symptoms besides blood in the stool, but I'm still a little worried about it. Should I take him to the vet, or give it a few more days?

By mach1busta — On Jun 05, 2009

I have a bulldog that has been bleeding through his rectum every time he goes to the bathroom. It's been almost a year now and the doctors have taken his blood and only come back with an enlarged prostate that may be causing this type of pressure. (The prostate is very large). However, when he comes back and I'm wiping him I do notice a little bean like deposit protruding from his anal area that is a blood like color. The blood when I wipe is a bright red color. He has not lost appetite and is very well otherwise. I just don't like to see the blood and it's been soo long I don't want it to be cancer.

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