One of the more common conditions for which I (Perry Jameson) see pets is diarrhea, specifically chronic diarrhea that has not responded to any therapy.

Before a patient sees me, they have already been to the family doctor and had preliminary testing as well as several attempts at therapy without success. What this also means is that the diarrhea has usually been going on for several months so everyone is ready for it to stop.

To figure out the cause, I try to narrow down where in the intestines the problem lies. Unfortunately, this means asking Mom and Dad to describe the diarrhea to me in detail. So if your pet is having diarrhea, it is important to observe certain characteristics.

Is there blood or mucus present? Does your pet strain, have to go more frequently, and are they going in the house when they formerly were completely house trained? When they go, is it a large volume or just small amounts? Has your pet lost weight or not?

Diseases of the lower end, colon or large bowel often have blood and mucus. They will usually defecate more frequently than they once did, producing smaller amounts. They may have such an increased urge to go that they start going in the house.

These pets are not constipated, but most owners think they are because they will repeatedly attempt to defecate with little to no produced feces. This is because the colon is inflamed, giving them the sensation they must go even when the colon is empty. Like when you have cystitis or prostatitis and feel like you have to urinate even though you just did and know your bladder is empty.

Before performing an extensive assessment, I always treat dogs with large bowel diarrhea for whipworms. Even if an examination is negative, I still treat. When examining the feces for parasites, we are looking for eggs. These eggs are not constantly being shed, which causes us to frequently miss infections.

In humans, dietary fiber promotes good colonic health. There are some dogs that have what we call a dietary responsive colitis. This means their symptoms resolve when we add a fiber source or change them to an increased fiber diet. So when deworming fails, this is my next step.

In some dogs, the bacteria Clostridium perfringens will cause diarrhea. The frustrating thing is this bacteria can also be present in dogs that are normal. Diarrhea appears to be caused when these bacteria begin to produce a toxin that damages the lining of the colon. Culturing for the bacteria, testing for the toxin and looking under the microscope for the organism have not been reliable. So I no longer test but instead treat and look for a response.

Since we treat with an antibiotic, we call this “antibiotic-responsive colitis.” Interestingly, the best antibiotic is Tylosin. This is not routinely used in people or pets, but in poultry. This means we have to get it compounded at specialized pharmacies, which fortunately now we have several in the tri-county area.

Most of the time we cannot eradicate the Clostridium completely, but our goal is to knock it down to a low enough level that little toxin is being produced. Interestingly, most of these dogs respond to fiber supplementation as well. This makes sense because fiber remains relatively intact until it reaches the colon where it can then have an impact on the bacteria that normally live there.

Dogs and humans have bacteria that normally live in our intestines, aiding with digestion. What we eat affects these populations. Certain foods, including fiber, promote healthy bacteria while other foods promote the growth of unhealthy bacteria. The fiber appears to promote the good bugs, which when keep the bad bugs in check.

Some dogs may have an inappropriate immune response to something in their diet. This is where a food product, usually a protein source, causes inflammation of the colonic lining resulting in diarrhea. This “dietary-responsive” disease is hard to diagnose directly. The frustrating issue with this disease is since we do not know the offending agent, all we can try are different diets until we find one that works. It also usually requires several weeks on a diet to know if it will be effective. I usually start with diets with a protein source the dog has never eaten, or a protein source broken down so small the immune system cannot recognize it.

Once I have tried these steps without success, I then recommend a colonoscopy. This allows me to visually assess what the colonic lining looks like and, more importantly, obtain samples for a pathologist to examine. This is how inflammatory bowel disease, fungal infections, and cancers are diagnosed.

Fortunately, most forms of large bowel diarrhea in dogs are treatable, making them not only comfortable but housebroken again.

Dr. Henri Bianucci and Dr. Perry Jameson are with Veterinary Specialty Care LLC. Send questions to

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