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Bloody Diarrhea in Dogs

Bloody Diarrhea in Dogs

The average pup should be examined by a veterinarian at least twice a year. During those other 363 days of the year, veterinary professionals rely on pet owners for help with assessing a patient’s health. Without your help, your doctor might not know that your dog is experiencing a health problem! This includes when dogs have bloody diarrhea. How does bloody diarrhea occur? When is it an emergency, and what can you do to help resolve it?

In This Article

What is diarrhea?

Diarrhea is when the consistency of a bowel movement has changed to a softer consistency. It results from increased motility of feces through the digestive tract and from decreased absorption of nutrients from food. Instead of having a formed stool, it can have the consistency of soft-serve ice cream or can appear more liquid like soup.  

Besides consistency, diarrhea can vary in its coloring and overall appearance. It can have small streaks of blood in it, or it can be grossly bloody and red. Sometimes, pets with diarrhea will have an increase in the amount of mucus seen. Bloody and mucous stools usually come from disease processes that affect the lower part of the digestive tract (e.g., the colon) while stools that are black in color or tarry in consistency come from the upper digestive tract (e.g., stomach and small intestines).   

In some cases, you may see other signs of illness besides diarrhea. Your dog may appear to be straining to defecate, which is often confused with signs of constipation. When posturing to defecate, dogs with diarrhea might yelp or cry. Dogs with systemic illnesses may also experience lethargy, vomiting, loss of appetite, and abdominal pain. 

What causes bloody diarrhea?

There are any number of problems that can cause bloody diarrhea. To put it simply, the majority of these problems cause inflammation of the lining of the colon or large intestine. This inflammation can result in the formation of small ulcers that can bleed, causing diarrhea to look bloody. In some cases, dogs can develop growths or polyps in the colon that can also bleed.

Stress is one of the most common causes of colitis (inflammation of the colon) and can cause bloody diarrhea that may resolve on its own. Dietary indiscretions and new foods or treats can also cause this kind of self-limiting diarrhea. Just like in people, dogs that are otherwise healthy have natural mechanisms in place to help clear mild diarrhea.

Infections due to viruses, bacteria, and intestinal parasites can also cause bloody diarrhea. Food allergies or hypersensitivities and malabsorptive disorders are usually responsible for chronic diarrhea, and dogs with inflammatory bowel disease can also suffer from chronic diarrhea. Bloody diarrhea often results from other underlying illnesses such as kidney and liver disease.  

Can you diagnose a cause for diarrhea?

In cases with mild, acute diarrhea, some dogs may improve on their own. Others may benefit from conservative therapy from your veterinarian, but testing is also important. Basic testing like fecal flotations can help rule out intestinal parasites, especially the type that can be passed from pets to people! Your vet may also recommend a direct fecal smear to look for other types of parasites.

If the diarrhea does not improve after a day or two, or it is not responsive to initial therapy, your canine companion may need additional testing. Veterinarians may recommend blood work and urine testing to evaluate the internal organs. Radiographs and ultrasound can help look for intestinal problems. In cases of chronic diarrhea, specialized testing like biopsies and fecal culture may be necessary.

Sometimes, your dog’s diarrhea may be a medical emergency. Dogs with fever, lethargy, and other clinical signs may need to be seen urgently. If your dog is extremely painful or losing a lot of blood from his bowel movements, this is also an emergency situation.   

How is diarrhea treated?

Diarrhea is best treated by addressing the initial cause. For most cases of acute, mild diarrhea, your vet may recommend conservative therapy. They may fast your pup for 12 to 24 hours and then introduce a bland therapeutic diet that is high in fiber and easy to digest. Prebiotics and probiotics can also help because dysbiosis (an imbalance between the “good” and “bad” bacteria in your dog’s intestines) usually occurs when pets have diarrhea.

Use of antibiotics for diarrhea can be controversial. Some antibiotics like metronidazole and tylosin have anti-inflammatory properties that can relieve intestinal inflammation. In some cases, antibiotics can actually cause diarrhea, and frequent use can lead to bacterial resistance. However, there are a few times when your vet may prescribe an antibiotic. Pets with giardiasis typically need metronidazole and a deworming medication called fenbendazole.

In cases of moderate to severe diarrhea, pets can become dehydrated. Subcutaneous or intravenous fluids may be necessary to help correct this deficit. Also, additional testing is necessary at this point to see if any additional treatments need to be prescribed. Deworming medications may be prescribed if parasites are confirmed with fecal testing, but there are times when they may be prescribed regardless of an unremarkable fecal test because parasites can shed eggs at varied times during their lifecycle.

Can diarrhea be prevented?

Most dogs who are on a well-balanced commercial diet will have healthy digestive tracts. Supplementing probiotics can be beneficial. Avoiding human foods and table scraps is best, and it is important to avoid switching between diets and dog treats abruptly. Routine preventive care visits and deworming can also help prevent diarrhea. Avoid giving human anti-diarrheal medications to your dog unless otherwise directed by your veterinarian.


Bloody diarrhea can be scary when it is first observed. It is best to collect the sample and bring it to your veterinarian as soon as you can. They are able to test it and may make recommendations based on stool testing. A small amount of blood may indicate mild gastrointestinal upset while large amounts may prompt an emergency trip to your vet’s office. Acute diarrhea may improve with rest and time, but any pet with diarrhea for more than a day or two should be seen by their veterinarian as soon as possible.

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Accreditations: Dr. Erica Irish, DVM attended University of Florida for her Bachelor's degree and graduated from the <a href="https://www.vetmed.ufl.edu/">University of Florida College of Veterinary Medicine</a>. Dr. Irish also has certifications from the <a href="https://phhp.ufl.edu/">UF College of Public Health and Health Professions</a>, the <a href="https://avdc.org/">American Veterinary Dental College</a> and she is an accredited veterinarian through the <a href="https://vsapps.aphis.usda.gov/vsps/public/VetSearch.do">United States Department of Agriculture</a> in Lake County, Florida. Dr. Irish currently practices as a veterinarian in Lake County, Florida.   Dr. Irish has been a veterinary contributor to <a href="https://bobospets.com/">Bobo's Pets</a> since December of 2020.