Chronic Large Intestinal Diarrhea in Dogs: Stories from My Diary-rrhea (part IV):

After your veterinarian has narrowed down the origin of diarrhea to the large intestine and if your dog is still suffering from diarrhea (continual or intermittent) for 3-4 weeks, it is time to delve in with a more aggressive workup.

Chronic Large Intestinal Diarrhea in Dogs: Stories from My Diary-rrhea (part IV):

With diarrhea that doesn’t go away, it is crucial to revisit the history and disease progression with your veterinarian.

Details that seem unimportant to you (or you don’t even think of) often unveil the case. 

For instance, knowing that the dog you just adopted came from a region where fungal infections are prevalent may make all the difference. Your veterinarian might not consider the diagnosis otherwise.

Dogs with chronic large bowel diarrhea usually appear healthy on physical exam.

This is not always the case, of course. 

If your dog shows signs of being unwell in addition to diarrhea, a minimum database of lab tests is important. It is a way to gain more information about how your dog’s health as a whole is doing. 

Laboratory tests may point towards a systemic problem. This gives your vet the information needed to know how aggressively and quickly action should be taken.

After ruling out obvious causes, large intestinal diarrhea calls for more invasive diagnostics.

Advanced diagnostics include:: 

  • fecal cultures
  • rectal cytology
  • x-rays
  • abdominal ultrasound, and
  • enemas with dye to outline the path of the colon

After performing all these tests and hearing that your vet still has no answers is very frustrating, and probably getting rather expensive. Hang in there.


A colonoscopy with biopsy is likely the least invasive of the next advanced diagnostics. It is also the most direct way to find out what is happening in the colon.

Colonoscopy and biopsies could reveal a number of diagnoses such as: 

  • fungal colitis
  • a mass (such as a malignant tumor or benign polyp)
  • bacterial infections, and
  • inflammatory bowel disease

Inflammatory bowel disease often affects both the colon and the small intestine and has many different types and underlying causes.  They are classified based on the predominant cell type affected: 

  • lymphocytic-plasmacytic
  • eosinophilic
  • neutrophilic
  • granulomatous,
  • or histiocytic

Each of these are worthy of lengthy discussion

Dietary hypersensitivity is all too often an overlooked cause of signs of chronic colitis.

Dietary allergies have usually nothing to do with a recent diet change. Hypersensitivities develop over time as a result of chronic exposure. 

There currently is no wonderful simple test to find out if your dog has a dietary allergy. It requires a strict exclusion diet for 6-8 weeks.

The options include a pre-made processed prescription diet or a home-cooked one.  This approach takes profound patience on the part of the dog owner while their dog is still experiencing diarrhea. However, it is the only current way to rule out dietary allergy.

In summary, the cause of your pet’s diarrhea is not the easiest thing for your veterinarian to diagnose. And it is certainly not easy for a dog owner to continually have the patience required to find the reason. This is especially true when it is a chronic problem requiring what feels like endless tests. 

There is often a simple reason for your dog’s diarrhea, be it intestinal parasites or eating human food to rich and fatty for your canine friend. However, many causes are serious and fatal if left untreated, such as lymphoma of the GI tract.

In all cases, diarrhea is a symptom of a disease. Finding out the disease is the difficult part.

The responsibility to pursue the cause of your pet’s diarrhea, and clean it up, lies in your hands.  You are your pet’s health care advocate. I encourage you to find a veterinarian that realizes this.

Chronic large intestinal diarrhea characteristics:

  • weight loss is rare
  • appetite is usually normal
  • vomiting occurs in a small percentage of patients
  • feces volume may be normal or even slightly smaller
  • normal to greatly increased frequency of defecation
  • increased urgency
  • straining
  • frank blood
  • mucous

Related articles:
Symptoms to Watch for In Your Dog: Diarrhea
A Tale of Many Tails—and What Came Out From Underneath 
Acute Small Intestinal Diarrhea
Acute Large Intestinal Diarrhea (Acute Colitis)
Chronic Large Intestinal Diarrhea
Chronic Small Intestinal Diarrhea

Further reading:
Chronic Diarrhea in Dogs

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