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Blood in Dog Stool: Why It Happens and What You Can Do

Written By
8 min read

Updated - Jul 19th, 2022

If you’ve found blood on your dog’s stool, take a deep breath – we’re here to help.

There are two kinds of blood you will typically see in a dog’s stool: bright red blood or black, tarry blood.

If you see bright red blood in your dog’s stool, this is called hematochezia. This blood is coming from the lower intestinal tract, the rectum, or the anus. Hematochezia can have several possible causes.

If you notice black, or tarry blood in your dog’s stool, this is called melena. This blood is coming from higher ‌in the dog’s digestive tract and is digested. There are many possible causes for this as well.

Why is there blood in my dog’s stool?

As we said earlier, there are two types of blood found in a dog’s stool and each means something quite different. Let’s look at both so you can identify what may be troubling your dog’s digestive system and give that information to your vet.

Hematochezia

Hematochezia is fresh, red blood in the stool. You may notice it on the surface of the stool. It’s common for this type of blood to be present on both fully formed stools or loose stools.

The bright red color indicates the blood has not traveled very far through the body and is undigested, giving it that bright red color. This type of bleeding usually begins in the rectum, colon, or anus.

Common causes of hematochezia

Parvovirus

This is a common reason for puppy diarrhea and bloody stools. Parvo can affect any puppy, but Rottweilers, German Shepherds, and Doberman Pinschers seem more affected. Symptoms may include:

  • Vomiting
  • Diarrhea
  • Loss of appetite
  • Blood in the stools
  • Lethargy

If you suspect your dog has contracted parvovirus, see your vet immediately.

Parasites

The most common intestinal parasites are hookworms, whipworms, roundworms, giardia, and coccidia (protozoans). A regular parasite prevention program can eliminate them. Your veterinarian examines your dog’s stools to prescribe specific anti-parasitic medication.

Rectal injuries and intestinal blockages

Dogs love to ingest anything that looks tasty to them. This can get them into trouble and cause irritations of the colon, punctures of the intestinal walls, intestinal blockages, diarrhea, and thus, result in bloody stools. The fresh blood will be bright red and should stop quickly. Keeping your dog away from hazardous materials and objects can reduce the risk of this issue.

Anal gland problems

Dogs have two scent glands located on either side of their anus, and inflammation or abscesses can result in hematochezia. 

Tumors

Colonic, rectal, anal, or anal gland tumors that bleed can cause hematochezia. 

Inflammation

Inflammatory bowel disease and severe colitis can cause hematochezia.  

Hemorrhagic Gastroenteritis

While not technically hematochezia, HGE is sudden, severe bloody diarrhea. The cause is unknown but may be bacterial. If you notice this kind of diarrhea in your dog, call a veterinarian immediately for assistance, as this condition can be fatal. 

Problems outside of the GI tract

Prostate disease, perineal hernias, or a fractured pelvic can all be causes of hematochezia in dogs. 

Other things to watch for:

  • Eating foreign objects, like toys, cooked bones that have sharp edges, rocks, sticks, clothing or towels, spoiled food, and garbage.
  • Rectal polyps and hemorrhoids: Some may protrude from the anus, or you may find blood on your dog’s bum. The surface of polyps and hemorrhoids bleed easily but also stop quickly. The vet can feel both with a rectal exam. Anytime you find bleeding from the rectum, a vet needs to determine the cause of the blood, or to rule out cancer or tumors. 
  • Dietary changes: Food intolerances, allergies, or changing to a new food too quickly can cause blood in the stool or a dog’s diarrhea. Always check with your vet to make sure you are transitioning from one food to the other in an appropriate amount of time to protect your dog’s digestive system.
  • Anal glands: The anal glands can become impacted, infected, or injured. Anal gland problems usually cause a dog to lick excessively ‘back there’ or scoot their butt, often signaling they need their anal glands expressed or vet treatment.
  • Stress: Extreme stress from fireworks, moving, a new pet, or a person joining the family can cause colitis – bloody diarrhea, sometimes with mucus. 
  • Bacterial infections: Salmonella and E.Coli, and are a few of the bacterial infections that can cause bloody diarrhea and blood in your dog’s stools. These are contagious to humans. Thoroughly wash your hands when touching dogs with these infections.
  • Inflammatory Bowel Disease (IBD): A chronic disease of the intestinal tract. Frequent inflammations caught early will produce bright red blood. If left untreated, the blood can become dark red.
  • Pancreatitis: The pancreas sends enzymes into the small intestines. When it gets angry, the small intestines become inflamed, and infection sets in, causing vomiting and serious diarrhea, which may contain mucus and show signs of blood.
  • Hemorrhagic Gastroenteritis (HGE): This is a sudden onset of vomiting, and large amounts of bloody diarrhea. Your dog will have abdominal pain or tenderness, lethargy, a fever, and decreased appetite. It is idiopathic, meaning the exact cause is often unknown, but it’s related to eating high-fat food or treats, eating foreign objects, and a host of other reasons. It’s most common in small breed dogs but can affect any dog.

Melena

Melena is the medical term for digested blood in stools. Many times, the stool will resemble coffee grounds. With melena, the blood could originate from the lungs, pharynx, esophagus, stomach, or upper small intestines. Because it travels further through the digestive system it is digested, making it look almost black. 

Your dog may poop in greater volume in cases of melena. If you’re not sure you’re seeing blood, try wiping some of the stool on a white paper towel. The redder pigments will be visible.

If you suspect your dog is showing signs of melena, you should contact your veterinarian immediately.

Common causes of melena

Toxins

Ingesting toxins like antifreeze or rat poison can cause melena. Also, toxic foods such as grapes, onions, and garlic will send your dog into a medical emergency ‌with black, tarry poop or bloody diarrhea. 

Ingesting blood

If your dog licks a bloody injury, has a dental disease that causes bleeding in their mouth, or even swallows the blood from a nosebleed. The stools will show digested blood or coffee-ground-looking poop when your dog has a bowel movement. 

Blood clotting disorders

Disorders that slow down the clotting of your dog’s blood can range from inherited disorders to acquired disorders. The ingestion of rat poison can also cause a clotting disorder and bleeding.

NSAIDs

Anti-inflammatory drugs can cause ulcers in your dog’s stomach which can bleed. The vet will monitor your dog’s health while on these medications, but you should also monitor the poop for signs of blood, catching any problems early. 

Post-surgery complications

Anytime your dog has undergone surgery and there is blood in their stool, contact your vet immediately. It could mean there is some internal bleeding.

Tumors or cancer

We never want to think about these, but they happen and can cause melena in your dog’s stools.

Pepto-Bismol

Used to treat diarrhea, Pepto-Bismol may turn your dog’s stool black temporarily. It will return to normal when the medication is completed. It can also cause gastric bleeding, so should only be given to your dog by recommendation of your veterinarian. 

What to do if you find blood in your dog’s stool

If you find blood in your dog’s stool, don’t ignore it, but also don’t panic. Tell your vet as soon as possible and if you can save a sample of the stool, it will be helpful. You need to ‌describe the blood as bright red or dark, but if you can’t tell, don’t worry, a stool sample or even a photo can help.

Your vet will determine if the situation is life-threatening and if there is a need for emergency care.

What to expect at the vet’s office

The treatment your dog needs will depend on the underlying cause of the bloody stool. This is determined through diagnostic tests and examinations. Here’s what may be recommended.

  • Physical examination and history 
  • Parasite test
  • Blood work to rule out anemia, infections, and platelet counts that may affect blood clotting ability
  • Metabolic or chemistry screening to check liver and kidney function
  • X-rays to look for foreign bodies in the digestive system and blockages
  • Ultrasound to look for tumors, check organs, or check for injuries
  • Endoscopy to examine the upper GI tract
  • Colonoscopy to examine the lower digestive tract

Depending on the underlying cause of the problem, your vet may recommend the following care:

  • Fluids for dehydration
  • Oral medications to reduce inflammation
  • Pain medication for stomach cramping and discomfort
  • Vitamin injections – inflammation interferes with vitamin absorption. Vitamin B12 is helpful.
  • Steroids to help the gut calm down and reduce inflammation
  • Probiotics to build up your dog’s immune system
  • Acid reducers for stomach ulcers, vomiting, or diseases that can cause hyperacidity
  • Surgery (Sometimes this is the only way to remove an object that your dog has swallowed)
  • Anti-parasitic medication if parasites or worms are present in the stool
  • Diarrhea medication

As you can see, there are many reasons your dog can have blood in their stool. Talking to your vet as soon as you notice it is important to help you get the best prognosis and resolution possible for your beloved fur buddy.

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Writer, Mom of a Fab Fur Fam of Five
Lynn is a writer and long-time Learning & Development Manager at a large PNW retailer. She's also mom to 3 dogs & 2 cats!