Colitis in Dogs

Colitis is an inflammatory condition of the colon (also known as the large intestine) that causes diarrhea. It is a common illness that will likely affect every dog at least once in their lifetime. As an emergency veterinarian, I see about half a dozen cases of colitis in dogs every twelve-hour shift!

Signs of Colitis in Dogs

Symptoms of colitis include diarrhea, cramping, flatulence, and an increased urgency to defecate. Diarrhea may start as a soft stool that is semi-formed and difficult to pick up from the ground in whole pieces. This often progresses into a soft “cow-plop” shaped stool and then to liquid. Diarrhea may contain mucus and sometimes fresh blood.

Some dogs will become so uncomfortable that they may squat and strain to defecate but produce no stool. This may look like they are constipated. But the reason they are straining is because they are trying to pass gas and liquid stool, not hard stool.

Dogs with colitis will often have a normal energy level and appetite. Vomiting, low energy, and decreased appetite are not typically symptoms of colitis unless the cause of colitis is also affecting the small intestine.

Causes of Canine Colitis

Colitis can have several causes including:

• Inflammatory bowel disease (IBD)
• Irritable bowel syndrome (IBS)
• Dietary indiscretion
• Intestinal parasites
• Bacterial or fungal infection
• Cancer

Your dog’s veterinarian will likely recommend a series of tests, including bloodwork, radiographs (x-rays), and fecal testing to determine the underlying cause of your dog’s colitis.

One of the first things your veterinarian will do to determine the cause of your dog’s diarrhea is obtain a complete history of your dog’s symptoms. This helps your veterinarian determine if his diarrhea is being caused by a problem in his small intestine, large intestine, or both. See the sidebar “Identifying Large Bowel vs. Small Bowel Diarrhea in Dogs” for more information.

IBD and IBS in Dogs

Inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS) are two very different diseases. IBD is a condition in which inflammatory cells of the immune system infiltrate the lining of the gastrointestinal tract. The gastrointestinal lining becomes thickened and does not properly absorb or process nutrients. IBD can affect the stomach, small intestine, large intestine, or any combination of these gastrointestinal segments.

IBS is a condition in which there is a temporary change in the motility of the colon. There are no structural changes to the lining of the gastrointestinal tract like there are with IBD. The cause of IBS in dogs is not known. But it is suspected that stress and anxiety are potential factors in the development of IBS.

Symptoms of IBD include chronic vomiting and diarrhea, weight loss, and decreased appetite. Dogs may also have black, tarry stool or bloody stool. Symptoms of IBS include an increased urgency to defecate and diarrhea that contains mucus. Some dogs may experience abdominal cramps and will act uncomfortable and restless. Dogs with IBS do not experience vomiting, weight loss, lethargy, or decreased appetite.

IBS is a diagnosis of exclusion. This means that other causes of diarrhea are ruled out by completing blood work, a fecal analysis, and imaging (such as radiographs and ultrasound). Biopsies of the small and large intestinal lining may be necessary to rule out other causes of diarrhea. These are obtained by endoscopy and colonoscopy.

Dogs with IBD may have specific alterations on their blood work that are suggestive of IBD. Sections of their intestines may appear thickened on abdominal ultrasound. But the only way to confirm a diagnosis of IBD is with histopathology of biopsy samples taken of the small and large intestinal lining.

Treatment of IBS may include temporarily feeding a prescription diet that contains a therapeutic amount of fiber. Some dogs may benefit from having a fiber supplement made from psyllium husk added to their diet. Medications to relieve your dog’s symptoms may include an antispasmodic such as loperamide (Imodium) or an anti-diarrheal such as kaolin pectin (Kaopectate). Consult with your veterinarian about which therapies would be best suited for your dog’s situation before administering anything at home.

Bismuth salicylate (Pepto-Bismol) can be given to dogs. However, this medication may interfere with the interpretation of abdominal radiographs (x-rays). If your dog is experiencing diarrhea and the cause is not yet known, avoid giving Pepto-Bismol until your dog has been examined by your veterinarian.

Dogs that are experiencing IBS symptoms suspected to be caused by stress may benefit from interventions to relieve anxiety. These interventions may include medications such as alprazolam, fluoxetine, or clomipramine. Non-pharmaceutical interventions may include an Adaptil collar or spray, Thundershirt, a calming supplement (such as Zylkene or Purina Calming Care), or a calming diet (such as Royal Canin Calm) may also be beneficial.

Treatment of IBD may include feeding a hypoallergenic prescription diet, such as Hills d/d, Royal Canin Selected Protein, or Purina HA Hydrolyzed Protein. Some dogs with IBD may benefit from treatment with an antibiotic that has an anti-inflammatory effect on the gastrointestinal tract, such as tylosin. Other dogs may require treatment with a medication that regulates their immune system’s effect on the gastrointestinal tract, such as prednisone, azathioprine, or cyclosporine.

Dogs with IBD may have a deficiency in a B-vitamin called cobalamin. Cobalamin is also known as vitamin B12. Your dog’s cobalamin level can be tested and monitored with a simple blood test. Cobalamin can be supplemented with an oral or injectable form of vitamin B12.

Dogs with mild to moderate IBD that respond to one or more therapies generally have a good prognosis. They may have periodic flare-ups that require a short-term addition of an anti-nausea or anti-diarrheal medication. Dogs with severe IBD may not respond as well to therapies and tend to have a poorer prognosis.

Histiocytic ulcerative colitis of Boxers (also known as granulomatous colitis of Boxers) is a specific form of inflammatory bowel disease that affects primarily Boxers and French Bulldogs. This disease affects young dogs and causes weight loss and bloody diarrhea. The bacteria Escherichia coli (E. coli) has been found inside macrophages within the lining of the colon of affected dogs. Macrophages are a type of white blood cell that encapsulate bacteria.

As with other forms of IBD, diagnosis of histiocytic ulcerative colitis is made with histopathology of biopsy samples of the colon lining. These samples are obtained during a colonoscopy. A bacterial culture and sensitivity completed on these samples is necessary to identify E. coli bacteria and determine the correct antibiotic treatment.

Dogs with histiocytic ulcerative colitis may respond well to antibiotics given over several weeks. Some dogs may require lifelong intermittent antibiotic therapy to minimize flare-ups of colitis.

Dietary Indiscretion

Dogs eat some of the oddest and most disgusting things. Sticks, rocks, trash, spoiled food, rabbit poop—you name it, they eat it. These items (and more!) can wreak havoc on a dog’s gastrointestinal tract.

Sticks, pointy rocks, and other non-food items with rough surfaces can cause trauma to the lining of the small and large intestine. This trauma may lead to inflammation of the gastrointestinal tract and the development of diarrhea.

Bacteria from spoiled or improperly cooked food can cause colitis in dogs. This is commonly known as “food poisoning”. Bacterial gastroenteritis is typically self-limiting and will likely resolve with supportive care.

Feeding a bland diet or a prescription gastrointestinal diet is typically all that is needed to resolve colitis in cases of dietary indiscretion. A home-cooked diet may consist of plain chicken breast, lean hamburger, or tilapia (a plain whitefish), and white rice. Prescription gastrointestinal diets—such as Hills i/d, Royal Canin Gastrointestinal, or Purina EN—may be appropriate (especially for those of us that don’t like to cook!).

Adding a probiotic may help to restore the altered gastrointestinal microbial flora and facilitate healing of the damaged intestinal lining. Your veterinarian may also prescribe an anti-emetic—such as maropitant (Cerenia) or ondansetron (Zofran)—to address any vomiting or nausea that may be present.

Intestinal Parasites

There are two intestinal parasites that can cause colitis in dogs. These are the canine whipworm Trichuris vulpis and the canine fluke Heterobilharzia americana.

Dogs contract Trichuris vulpis by ingesting whipworm eggs. The eggs hatch in the small intestine and develop into larvae. The larvae migrate to the colon and develop into adult whipworms. Diagnosis is by finding whipworm eggs in a stool sample. Most dewormers are effective at treating a whipworm infection.

The canine fluke Heterobilharzia americana causes a disease known as schistosomiasis. Schistosomiasis affects the liver and both the small and large intestine. Dogs contract schistosomiasis by swimming or wading in bodies of freshwater that contain pond snails infected with H. americana. This fluke is prevalent in the Gulf Coast states, southern Atlantic states, and regions along the southern Colorado River basin.

Schistosomiasis can be diagnosed by a specialized fecal PCR test or by finding H. americanum eggs on a saline fecal sedimentation test. These are not routine fecal tests. They must be specifically ordered by your veterinarian if your dog is suspected of having schistosomiasis.

Schistosomiasis is treated with a combination of two deworming medications – praziquantel and fenbendazole. Some dogs require more than one treatment cycle to eliminate the parasite.

Fiber-Responsive Colitis in Dogs

Fiber-responsive colitis, like IBS, is a diagnosis of exclusion. There is no diagnostic test for fiber-responsive colitis in dogs. Other causes of colitis should be ruled out before concluding that a dog has fiber-responsive colitis.

Dogs with fiber-responsive colitis may have one or more problems that lead to having chronic or acute-on-chronic diarrhea. Their colon may move feces along too quickly, causing loose stool. The bacterial flora of their colon may not have the correct ratio of beneficial bacteria to create formed stool.

Fiber has several benefits for both the small and large intestine. Fiber helps to regulate water balance in the colon, bacterial gut flora in the small and large intestine, and the amount of time the colon takes to create formed feces.

Dogs with fiber-responsive colitis may require lifelong addition of prebiotic, soluble, and insoluble fiber sources to their diet. Fiber sources include (but are not limited to) psyllium husk, flaxseed, fruits and vegetables, and bran. Talk to your veterinarian about an appropriate fiber supplement for your dog if he is suspected to have fiber-responsive colitis.

Other Causes of Canine Colitis

Other causes of colitis in dogs include pythiosis, histoplasmosis, and cancer. These are not common. Dogs with one of these conditions will show other signs of illness due to effects on other parts of the body. Other symptoms of these conditions may include weight loss, vomiting, lethargy, and loss of appetite. Diagnostics for these conditions typically include bloodwork, abdominal imaging, and obtaining biopsy samples of affected areas of the colon.

Acute vs. Chronic Colitis in Dogs

Acute colitis is characterized by symptoms that only last a few days and require little, if any, intervention to resolve. Acute colitis may be caused by irritable bowel syndrome, dietary indiscretion, or eating spoiled or contaminated food.

Chronic colitis may last weeks to months. Dogs with chronic colitis may have symptoms that wax and wane—their symptoms may start to improve but then become worse. Chronic colitis does not typically resolve on its own. Chronic colitis may be caused by inflammatory bowel disease, fiber-responsive colitis, intestinal parasites, schistosomiasis, pythiosis, histoplasmosis, or cancer.

There is a third category called acute-on-chronic colitis. Acute-on-chronic colitis is when the symptoms of colitis last a few days, resolve, and then return. Symptoms may return a few days, weeks, or months after the initial incident. Sometimes this is called an acute flare-up of a chronic disease. Causes are similar to those for chronic colitis.

Treatment and Prognosis for Dogs with Colitis

Treatment of colitis in dogs is aimed at identifying and treating the underlying cause. Your veterinarian may recommend submitting a sample of your dog’s stool to a diagnostic laboratory for a fecal flotation analysis or a fecal PCR test. These tests screen your dog for intestinal parasites.

Your veterinarian may also recommend bloodwork, including a complete blood count (CBC), chemistry panel, and baseline cortisol level. Abdominal radiographs (x-rays) or an abdominal ultrasound may also be recommended. Additional tests may be recommended depending on your dog’s other symptoms, age, breed, and potential exposure to particular parasites, fungi, or algae.

Dogs with colitis for which no identifiable cause is found may be treated with supportive care. Supportive care treatments may include giving prebiotics and probiotics, feeding a bland or prescription gastrointestinal support diet, adding soluble and insoluble fiber to your dog’s food, or administering kaolin-pectin.

Dogs being treated supportively for colitis whose symptoms either worsen or do not improve in two to three days should be re-evaluated by their veterinarian.

Treating colitis with an antibiotic—such as metronidazole—is not warranted unless an underlying bacterial or protozoal infection has been confirmed with diagnostics. Metronidazole (also known as flagyl) has an anti-inflammatory effect on the gut that can quickly resolve diarrhea, but it can negatively impact the gut bacterial flora and increase the risk of having future colitis episodes.

Dogs with uncomplicated colitis caused by intestinal parasites, dietary indiscretion, or stress are more likely to have an excellent prognosis for recovery. Dogs with colitis caused by IBD or fiber-responsive colitis can have a good prognosis with lifelong management of their illness. Dogs with uncommon but more serious causes of colitis typically have a more guarded prognosis for recovery.