Causes of Blood in a Dog's Stool

Blood in a dog's stool can be the sign of numerous medical conditions. Although one incident of bloody stools might not be cause for immediate concern, repeated episodes might indicate a serious health problem.

Parasites

Parasites are the most common cause of blood in a puppy's stool. Common canine parasites include roundworms, whipworms and hookworms.

Dietary Indiscretions

Blood in a dog's stool can be caused by changes in the dog's diet, overeating, food allergies and the ingestion of spoiled food or non-food material. Dietary problems might also trigger sudden, extreme bouts of diarrhea and vomiting.

Parvo

Parvo is a serious canine health condition that can cause bloody stools as well as lethargy, appetite loss, diarrhea and vomiting.

Bleeding Disorders

Blood clotting disorders, or coagulopathies, might cause a dog to bleed internally and pass bloody stools. This can be caused by hemophilia, liver disorders, organ failure or ingestion of rat poison.

Ingestion of Blood

Dogs sometimes pass black, tarry stools because they ingested blood. They might have a bloody mouth injury or licked blood off a body wound.

Cancer

Canine cancers, particularly colon cancers, can cause dogs to pass dark black stools. Cancer is a more common diagnosis for older dogs than for puppies.