Colitis is a general term for inflammation of the large intestine. It's estimated that about a third of all dogs with chronic or episodic diarrhea suffer from some form of colitis. Cats are commonly affected by this disease process, too.

For both companion animal species, colitis can be classified (according to the predominant cell types in the intestinal lining) as eosinophilic, plasmacytic-lymphocytic, histiocytic and granulomatous. Some are understood to have a genetic basis as a disease of the immune system (as with the plasmacytic-lymphocytic and histiocytic variety in dogs), while others are idiopathic (meaning we don't have an explanation as to why they occur). The majority of colitis cases in pets, however, are the result of one of more of the following:

  • Infectious diseases (such as bacteria, viruses, fungi, or parasites)

  • Dietary intolerance (or allergy)

  • Dietary indiscretion

  • Cancer of the colon

  • Pancreatitis

  • Antibiotic or other drugs

Symptoms and Identification

The most common symptoms of colitis are diarrhea (often bloody or "slimy" with mucus) and abdominal pain. In cats, in particular, the pressure on the colon can sometimes lead to vomiting as well. Weight loss (especially in cats), dehydration (especially if the diarrhea is very watery) and lethargy are commonly associated with colitis as well.

Colitis can be chronic (constant), acute (come on suddenly) or chronically episodic (meaning that it comes and goes).

Because colitis has a variety of different forms and causes, and because the common nature of the symptoms can be easily confused with other diseases, diagnosis is aimed at determining the root of the problem.

For any pet with severe diarrhea, a physical examination, fecal examination, basic blood work and X-rays are usually in order. Should this happen recurrently, or when the symptoms do not subside with symptomatic treatment, additional, gastrointestinal-specific blood tests are run along with possibly an ultrasound and, most effectively, a colonoscopy (in which we look at the lining of the intestines and take a sample of tissue for biopsy).

Affected Breeds

For histiocytic colitis (also called "histiocytic ulcerative colitis") the most commonly affected breeds are the Boxer and the English Bulldog, but colitis of all varieties occurs in all breeds of dogs and cats.


The treatment of colitis depends on the nature of its cause. For example, colitis caused by parasites is typically treated with parisitacides, whereas colitis caused by dietary indiscretion (eating a rotting carcass, for example) is treated with antibiotics and a bland diet.

When the cause, however, has been found to be an aberration of the immune system in which the lining of the intestine is predisposed to inflammation (as in plasmocytic-lymphocytic colitis or histiocytic colitis), drugs like prednisone (a corticosteroid) is often employed.

Pets who suffer this problem may require special diets that fail to stimulate the immune system adversely. Simple, bland diets may be sufficient for some, either episodically or for long-term use.

Veterinary Cost

The cost of diagnosis for those who suffer from severe forms of the disease can be very high when you consider the price of ultrasounds, colonoscopies and expensive blood work. Because internal medicine specialists are often employed in reaching a definitive diagnosis, high costs are associated with their advanced training and experience.

For severe cases, costs may run into the low thousands of dollars. For those who suffer intermittent forms that prove manageable for owners without having to rely on extensive testing, the additional cost of frequent veterinary visits, medication and special diets can still be significant, usually priced at $100 to $300 per episode if it's not severe.


Preventing individual episodes of colitis is possible for certain forms of the problem. Using preventative therapies for intestinal parasitism and keeping pets from eating foods they may be sensitive to is essential. The use of prescription diets may be sufficient for some.

For pets with more severe, immune-system based colitis, however, preventing the disease is all about breeding. Though we don't understand the mode of inheritance of these forms of colitis, we believe that these dogs and their parents (and possibly their siblings) should not be allowed to procreate.


Dimski, D.S. 1995. Therapy of inflammatory bowel disease. In J.D. Bonagura and R.W. Kirk (eds.) Kirk's Current Vet. Therapy XII Small Animal Practice. pp. 723-728. W.B. Saunders Co., Toronto.

Jergens, A.E. and Willard, M.D. 2000. Diseases of the large intestine. In E.J. Ettinger and E.C. Feldman (eds.) Textbook of Veterinary Internal Medicine, Chapter 138. W.B. Saunders Co., Toronto.