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April 25, 2019 – It is the rare dog owner that hasn’t had to deal with cleaning up a dog poop mess in the house. Apart from the occasional accident that happens during toilet training, or when we let a dog linger inside for too long, inappropriate defecation often is a sign of intestinal troubles.

As a rule, veterinarians divide diarrhea into two broad categories based on where in the intestinal tract the diarrhea originates – small bowel (originating in the small intestine) and large bowel (originating in the large intestine). Although unpleasant, paying attention to stool quality can give your family veterinarian valuable clues that can point them toward a diagnosis and best treatment.

Characteristics of small-bowel diarrhea include:

  • Large volume
  • Usually watery
  • Frequency might or might not be increased

Diseases that cause small-bowel diarrhea include intestinal viruses, intestinal parasites, dietary indiscretions and chronic enteropathy (inflammatory bowel disease)

Characteristics of large-bowel diarrhea include:

  • Small volume
  • Usually semi-formed or cow-patty consistency
  • Increased frequency of defecation with straining
  • Often contains mucus

Diseases that cause large-bowel diarrhea include stress colitis, fiber responsive diarrhea and intestinal parasites.

Sometimes, we can see characteristics of both small- and large-bowel diarrhea in a dog. This can occur when a disease process involves both the small and large bowel. We also can see this pattern when a patient starts with small-bowel diarrhea that causes secondary irritation of the large bowel.

Blood in the stool can be noted in both small- and large-bowel diarrhea. Blood in the stool can take several forms:

  • Digested blood from the stomach or small intestine results in black, tarry stools
  • Fresh streaks of blood mixed in the stool or coating the stool usually indicate a large bowel problem
  • Profound bloody diarrhea is common with parvovirus infections and with hemorrhagic gastroenteritis

One slight exception to the small bowel-large bowel rule is in cases of exocrine pancreatic insufficiency. This condition occurs when the pancreas doesn’t make enzymes needed for nutrient digestion. This results in large volume, pale-colored and very smelly stools.

Concurrent vomiting is more common with small intestinal diseases although some studies suggest that vomiting occurs in 30% of dogs suffering from large-bowel problems.

If your dog has diarrhea, call your family veterinarian for guidance. In many cases, the loose stools will resolve without treatment. Your family veterinarian is the best person to help decide if and when further diagnostics or treatment is needed.

Morris Animal Foundation has funded more than 50 studies and invested $1.2 million dollars in studies focused on gastrointestinal tract problems. We were instrumental in funding the groundwork for the development of the first parvovirus vaccine and we funded studies on new diagnostic tests for exocrine pancreatic insufficiency. We’re on the cutting edge of gastrointestinal research, from the use of probiotics to studies looking at the gut microbiome. Check out all our studies and learn how you can help our dogs live longer, healthier lives.


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