Pet owners are often alarmed by seeing blood in their dog’s stool, and for good reason. While there are multiple potential causes of bloody stool in dogs (some more serious than others), this is never normal, even if only a small amount of blood is noted. While some causes of blood in the stool are relatively simple to treat, others constitute medical emergencies. Read on to find out a few common causes of bloody stool, and what actions you should take if you notice this.
What are common causes of bloody stool in dogs?
Parvovirus is a potentially fatal disease most often affecting young, unvaccinated, or incompletely vaccinated dogs that causes lethargy, decreased appetite, and bloody diarrhea and/or vomiting. It is very contagious and is spread through contact with contaminated fecal material. Dogs with parvo require immediate treatment for the best chance of survival. 1
Common intestinal parasites like roundworms, hookworms, whipworms, Giardia, and coccidia can cause inflammation and damage to the intestines resulting in diarrhea and/or bloody stool.2 These are often easily treated with the appropriate medications prescribed by a veterinarian. Monthly heartworm preventatives commonly help protect against certain types of intestinal worms as well,3 so keeping your dog up-to-date on this is important.
Colitis is a general term meaning inflammation of the colon. It can be due to multiple causes, including stress, intestinal parasites, infections (E. coli, Salmonella, etc.), or ingestion of unfamiliar foods, contaminated food or water, or foreign objects. Colitis is associated with frequent diarrhea that often contains small amounts of blood, and may range from mild to severe.4
Pancreatitis is inflammation of the pancreas, an organ that helps digest food and regulate blood sugar. Pancreatitis may be caused by ingestion of a fatty meal or steroid medication, but also often develops with no known cause. Symptoms include lethargy, decreased appetite, vomiting, diarrhea, and abdominal pain. While some dogs recover well from pancreatitis, in others, the condition may become chronic or life-threatening.5 Treating this right away is important to prevent serious complications.
Dogs having large amounts of blood in the stool may be diagnosed with hemorrhagic gastroenteritis, or HGE. This is a condition characterized by sudden vomiting and very bloody diarrhea. The cause of HGE is unknown, but it may be related to an overgrowth of Clostridium bacteria in the intestines,6 and is often seen in small or toy breed dogs. Due to the severity of this condition, affected dogs require medical treatment as soon as possible.7
Anal gland disease
Anal glands are scent glands located on either side of a dog’s anus; they produce a foul-smelling liquid that is normally expelled with the feces during defecation. However, in some dogs, the anal glands are not expressed properly, and can become infected and painful. If the glands become too full, they can also rupture, causing a wound near the anus. Due to their proximity to the anus, infected or ruptured anal glands can cause small amounts of blood to appear in the stool on defecation. Anal gland disease requires prompt medical treatment, but is not life-threatening.8
What should I do if I notice blood in my dog’s stool?
Contact your veterinarian
Since some causes of bloody stool are more serious than others, contacting your veterinarian for guidance is a good first step for any owner noticing blood in their dog’s stool. Veterinary professionals can learn more about your dog’s specific situation to determine what potential causes are most likely, and whether the dog should be seen, or if at-home treatment with close monitoring is an appropriate course of action.
Take young puppies with bloody stool to the veterinarian immediately
Young puppies that have not been vaccinated, have not yet completed their vaccines, or only recently completed their vaccinations (within 1 month) should be taken to the veterinarian immediately if bloody stool is noted, as this can be a sign of parvovirus.
Take dogs with large amounts of blood in the stool to the veterinarian immediately
Dogs having large amounts of blood in the stool (more than a few drops or small streaks) should be taken to the veterinarian immediately to prevent significant blood loss or dehydration.
Take dogs with additional symptoms to the veterinarian as soon as possible
Dogs with lethargy, decreased appetite, vomiting, diarrhea, or abdominal pain in addition to the bloody stool should see a veterinarian as soon as possible, as multiple symptoms may indicate a more serious illness that requires veterinary treatment.
Take dogs with black, tarry stool to the veterinarian immediately
Dogs experiencing bleeding in their upper gastrointestinal tract (the stomach or adjacent small intestine) will have black, tarry stool, rather than having bright red blood in the stool. In this case, the stool looks black because the blood is digested by the rest of the intestines as it passes through, which changes its appearance.9 If you notice that your dog has a black, tarry bowel movement, you should take the dog to the veterinarian right away, as this can indicate an emergency requiring immediate care.
You should briefly examine your dogs’ bowel movements daily to ensure they are normal. Fecal material can convey valuable information about your dog’s health, and it is important to note any changes in the frequency, consistency, quantity, or color of your dog’s bowel movements. Blood in the stool is a concerning finding that can be due to relatively benign or potentially life-threatening causes. For this reason, you should consult your veterinarian as soon as you notice this, and monitor your dog closely for other signs of illness. Bloody stool in young puppies, large amounts of blood in the stool, or black, tarry stool are always emergencies and should be addressed immediately by taking your dog to the veterinarian.
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- Common dog diseases. ASPCA. Accessed February 14, 2022.
- Internal parasites in cats and dogs. AVMA. Accessed February 14, 2022.
- Gates MC, Nolan TJ. Declines in canine endoparasite prevalence associated with the introduction of commercial heartworm and flea preventatives from 1984 to 2007. Vet Parasitol. 2014;204(3-4):265-268. doi:10.1016/j.vetpar.2014.05.003
- Weir M. Colitis in dogs. VCA Animal Hospitals. Accessed February 14, 2022.
- What is pancreatitis? AAHA. Accessed February 14, 2022.
- Sindern N, Suchodolski JS, Leutenegger CM, et al. Prevalence of Clostridium perfringens netE and netF toxin genes in the feces of dogs with acute hemorrhagic diarrhea syndrome. J Vet Intern Med. 2019;33(1):100-105. doi:10.1111/jvim.15361
- Pachtinger G, Brashear M. Hemorrhagic gastroenteritis. AAHA. Accessed February 14, 2022.
- Rubin SI. Disorders of the rectum and anus in dogs. MSD Veterinary Manual. Accessed February 14, 2022.
- Moore LE. Digestive system: introduction. In: Morgan RV, ed. Handbook of Small Animal Practice. 5th ed. Elsevier; 2008:293-294.