Inflammatory bowel disease (IBD) is perhaps the most common cause of regular, recurrent diarrhea (and vomiting) in dogs and cats.
This is a diagnosis of exclusion. In other words, all other causes of stomach upsets need to be ruled out before a veterinarian concludes that IBD is present. Why IBD happens isn’t known, but it is thought that something triggers the local immune system in the gut wall, which, once activated, causes inflammation.
This trigger factor needs to be identified and removed for a pet to feel better, but this isn’t always possible, unfortunately. Many sufferers require medication to control the inflammation.
IBD relates to the gastrointestinal tract, and symptoms include general sickness and diarrhea. The diarrhea may contain mucus or blood and is often associated with fecal straining.
Pets with IBD lose weight easily, despite having a good appetite, which makes it distressing for the dog or cat — and the pet’s human.
Experts think that a fault in the immune system causes tissue in the gut wall (designed to fight infection) to work overtime. It incorrectly identifies a perfectly harmless substance as something that shouldn’t be there and triggers a cascade of events that lead to bowel wall inflammation.
A vicious circle starts when the inflamed bowel lining is sensitized and becomes further inflamed, sometimes so much so that blood seeps from the lining and is passed out in the feces. Also, in an attempt to protect itself, the bowel produces mucus as a bandage layer, trying to give the wall a chance to heal.
Food allergies or intolerance are thought to be a major risk factor for IBD. In the same way that hay fever sufferers sneeze around pollen, the bowel decides a food protein is an allergen and sets about protecting itself in IBD, which then causes the symptoms.
Diagnosis partially depends on ruling out other causes of upset stomachs.
This means screening for infection and parasites by checking fecal samples for the presence of bacteria, eggs or larvae.
Routine blood work checks that dogs or cats have adequate protein levels in their blood and their organ function is healthy. Diarrhea can be a common symptom of many organ-related problems, such as liver disease. Blood tests may also check that the bowel wall is healthy and contains adequate Vitamin B levels and that the pancreas is producing enough digestive juices.
Ultimately, a firm diagnosis is made following a biopsy of the gut wall. However, bowel surgery is associated with a high complication rate. If all other causes of diarrhea have been ruled out, some vets start the patient on trial treatment rather than putting the animal through exploratory surgery.
At the top of the list for many animals with IBD is a trial hypoallergenic diet. By removing sources of possible allergens, the stimulus for inflammation is removed, and this can be sufficient to settle some cases down.
For more persistent cases, a course of the antibiotic metronidazole can help. As well as having an antibacterial and anti-protozoal effect, it also modulates the immune response of the bowel. Particularly challenging cases may need steroids or other more potent anti-inflammatory drugs, such as azathioprine (dogs only), to control the symptoms.
Key to prevention is identifying the trigger factor, such as a particular food the animal cannot tolerate, and removing it from the diet.
- “Management of canine inflammatory bowel disease.” Marks. Comp Cont Ed Pract Vet, 20: 317–332.
- “Idiopathic inflammatory bowel disease in dogs and cats.” Jergens, Moore & Haynes. JAVMA, 201: 1601–1608.
This pet health content was written by a veterinarian, Dr. Pippa Elliott, BVMS, MRCVS. It was last reviewed Oct. 13, 2018.