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July 30, 2019 – Cats’ fastidious behavior when it comes to poop makes it easy to clean up, but also can mask changes in stool that would signal a potential health problem. Although diarrhea is less of a problem in cats than dogs, there are some similarities between the two species when it comes to underlying causes – as well as a few differences.

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 of your pet can give your family veterinarian valuable clues to 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 in cats include intestinal viruses, intestinal parasites, cancer, hyperthyroidism 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, intestinal parasites and megacolon (more on this condition later).

Sometimes, we can see characteristics of both small- and large-bowel diarrhea in a cat. 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. This can be a challenge to diagnose in cats since their stools tend to normally be dark in color.
  • Fresh streaks of blood mixed in the stool or coating the stool usually indicate a large-bowel problem

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

Hyperthyroidism in cats frequently causes diarrhea and can be easily overlooked in a diagnostic work-up for diarrhea. Many routine bloodwork panels for cats have a screening test for this disease.

Another disease seen almost exclusively in cats is megacolon. This disease begins when cats become constipated. The large intestine stretches but loses tone which leads to more constipation. Cats will often leak a little loose stool around the hard feces which can be interpreted by a cat owner as diarrhea. Megacolon is easily diagnosed on a physical examination and via X-ray.

If your cat has diarrhea, call your family veterinarian for guidance. In some 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’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 cats everywhere have longer, healthier lives.