Colitis in dogs: symptoms, causes, diagnosis and treatment

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The term colitis refers to an inflammation of the colon. It can be acute (sudden onset and short-lived) or chronic (present for at least 2-3 weeks or characterized by episodic recurrence).

Colitis has no association with the age or gender (male or female) of the dog with the exception of histiocytic ulcerative colitis, which affects young boxer dogs more frequently.


In most cases, colitis causes a number of symptoms:

  • loose stools with bright red blood and mucus
  • increased frequency of defecation acts (often several times a day)
  • emission of small quantities of feces

Generally, dogs with acute colitis show no signs of systemic disease. In contrast, dogs with chronic colitis can experience clinically significant weight loss.

An occasional episode of acute colitis is not uncommon. However, it is important to pay attention to a possible frequent recurrence of the symptoms or to an aggravation of the same, especially if they include systemic signs of the disease. Although healthy dogs may experience occasional episodes of vomiting, it is essential to report repeated vomiting to the vet promptly, lack of appetite, slimming and lethargy.


Since the clinical symptoms of colitis can be similar to those caused by other pathologies, during the initial phase of the evaluation of the animal it is appropriate to carry out a differential diagnosis.

In fact, there are many types of inflammatory disorders that can cause or be associated with colitis. These ailments are collectively known as “inflammatory bowel disease”, as the clinical symptoms of several specific ailments are very similar to each other. To establish appropriate treatment, definitive diagnosis of the specific disorder is required.

Inflammatory bowel diseases include:

  • Lymphocytic-plasmacytic colitis. It is the most common inflammatory bowel disease in dogs. The definitive cause is not known, but is believed to be caused by an overreaction of the immune system.
  • Histiocytic ulcerative colitis. It is characterized by ulcers and inflammation of the colon. It is most commonly observed in young boxer breed dogs.
  • Granulomatous colitis. It is a poorly understood pathology of the colon resembling Crohn’s disease that affects the human being. The term “granulomatous” refers to the involvement of specific types of inflammatory cells present in the colon.
  • Eosinophilic colitis. It is characterized by the infiltration of eosinophils (a type of white blood cell associated with allergic reactions or parasites) in the affected intestine and, in a variable way, also by the increase in circulating eosinophilic cells. The cause is unknown, but the involvement of food allergy or parasitic infection is possible.

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Colitis symptoms can be caused by many infectious agents, including:

  • Bacteria (Clostridia, Salmonella, E. coli, Campylobacter and others)
  • Fungal agents (such as causative agents of histoplasmosis, pythiosis and prototecosis)
  • Protozoan parasites (Trichomonas, Ameba, Balantidium, Giardia)

Even the food intolerance or allergic reactions can cause colitis. In this case, colitis often arises as a reaction to a specific protein, but it can also be associated with lactose, high fat content and some food additives.

Food indiscretion can cause acute colitis (sudden onset and short course). Examples include: ingestion of spoiled food, overfeeding, ingestion of foreign bodies and sudden food changes.

Colon cancer can cause symptoms similar to those that occur in colitis, such as mucus and bright red blood in the stool, defecatory effort, increased frequency of defecation and painful defecation. The most common types of colon cancer in dogs are adenocarcinoma and lymphosarcoma.

THE trauma, both internal (foreign bodies) and external (for example, the dog is hit by a car), can cause colitis.

L’intussusception (intestinal invagination) can cause partial or total occlusion and result in symptoms such as defecatory exertion or blood or mucus in the stool.

There hemorrhagic gastroenteritis it is a dramatic and potentially fatal condition, the cause of which is unknown. It occurs primarily in small dog breeds. It is characterized by the sudden onset of bloody profuse diarrhea and occasional vomiting.

There pancreatitis (inflammation of the pancreas) can cause the presence of blood and mucus in the stool.

Antibiotic-associated colitis may arise following the administration of certain antibiotics. Typically, it is self-limiting and ceases once antibiotic treatment is stopped.

The clotting disorders (coagulopathies), including clotting problems due to liver failure, some rodenticides and thrombocytopenia (low platelet count), can result in blood in the stool and be mistaken for colitis.


To identify colitis and rule out other conditions that can cause similar symptoms, it is necessary to conduct diagnostic tests, including:

  • Complete clinical history and thorough physical examination (including digital rectal examination and thorough abdominal palpation) are the first steps to establish an accurate diagnosis.
  • In cases where colitis is suspected, several should be performed fecal studies aimed at assessing the presence of parasitic worms and protozoa eggs (faecal flotation, direct faecal smear and zinc sulphate tests for the search for Giardia and Balantidium). Parasitism is one of the most common causes and contributing factors in dogs with colitis.
  • Complete blood count test. In the case of infectious and inflammatory disorders, it can identify a high number of white blood cells. It can also reveal anemia due to chronic blood loss in the stool in some forms of colitis.
  • Biochemical serum tests. Typically, the values ​​in dogs with colitis are normal, but such tests help identify abnormalities in other body systems (pancreas, liver) that can cause similar symptoms. These tests also help determine the general health of the dog.
  • Urine analysis. It can be done to evaluate kidney function.
  • Abdominal radiographs. Typically, the outcomes are normal but can reveal evidence of abnormalities affecting other organs (lymph nodes, prostate gland) that can put pressure on the colon and cause symptoms of colitis.
  • Thoracic radiographs. They are often recommended in older dogs and in dogs suspected of having cancer in order to evaluate a possible metastasis of lung cancer.
  • Determination of trypsin-like serum immunoreactivity (TLI). It is a blood test often recommended for all dogs with chronic colitis in case the other tests are not diagnostic. This examination will help identify some pancreatic conditions (pancreatic enzyme deficiency) that can cause diarrhea and be confused with colitis.

Should the above tests prove to be inconclusive and in order to ensure optimal medical treatment, the veterinarian may recommend further diagnostic tests. These are selected on an individual basis according to each specific case:

  • Matt enema (an X-ray contrast medium is placed directly in the colon followed by abdominal radiographs). It is sometimes recommended for the identification of masses or changes in the colon that would be difficult to view on blank radiographs. This procedure is often a source of discomfort for the dog, therefore it is not carried out frequently.
  • Abdominal ultrasound. It allows the visualization and evaluation of internal organs (colon, regional lymph nodes and prostate gland) in a non-invasive way. It also allows the collection of abnormal tissue samples using an ultrasound-guided needle or biopsy tool.
  • Colonoscopy (it is performed only after a certain period of fasting and several cleaning enteroclisms) with the aid of a flexible endoscope equipped with optical fibers. Allows direct visualization of the internal surface of the colon for the identification of polyps, tumors, chronic inflammation and sometimes parasites. During this procedure, it is possible to take small biopsy samples of the internal surface of the colon for microscopic examination by a veterinary pathologist. Colonoscopy requires only a short hospitalization, but this procedure may require the intervention of a specialist. Typically, colonoscopy is performed after other routine tests have proved inconclusive and the dog has not responded to conservative treatment (antiparasitic drugs and food changes).


Many treatments are available for colitis. In order for appropriate treatment to be instituted, a specific cause (if possible) should be identified. In the absence of underlying conditions, outpatient treatments, such as pesticides or food changes, may initially be recommended in healthy dogs with colitis. In the event that this approach proves ineffective, further examinations are generally recommended (colonoscopy and biopsy) in order to increase the chances of a specific and accurate diagnosis. Complete resolution of clinical symptoms may not be possible, even with an accurate diagnosis and appropriate treatment.

Treatments may include one or more of the following options:

  • 24-48 hour fasting with gradual introduction of a mild (light) diet followed by the gradual reintroduction of the dog’s normal diet. It can be sufficient treatment for many dogs with acute colitis.
  • In dogs with chronic colitis, food changes can be tried by switching to the use of hypoallergenic diets. To control colitis and eliminate the need for further medical treatment, sometimes a homemade diet or a commercial diet containing a “new” protein source (which the dog has never eaten before) is sufficient. During this trial period, the dog’s feeding must consist exclusively of the hypoallergenic diet. Dogs that respond to this approach are believed to have a food allergy that manifests as colitis.
  • Sometimes, in dogs with colitis, fiber supplementation (adding fiber to the dog’s normal diet or choosing a naturally high fiber diet) is of great benefit.
  • Antiparasitic treatment (deworming products, antiprotozoal drugs) is indicated to eliminate the possibility of parasites that are intermittently expelled in the feces (whipworm, Giardia). Parasites are one of the main causes of colitis and this approach is usually chosen as the first step in managing colitis.
  • Antibiotic treatment can play an important role in the management of colitis. Although antibiotics are useful if a bacterial cause of colitis is identified, these drugs are sometimes useful even in the event that a bacterial cause has not been established. In these cases, the commonly used antimicrobial agents include: metronidazole, sulfasalazine and tylosin.
  • Anti-inflammatory and immunosuppressant drugs (drugs that suppress the immune system), such as corticosteroids and the azathioprine immunosuppressant agent, are generally reserved for cases where there is a strong suspicion of immune-mediated colitis (based on the results of microscopic examination of samples biopsies obtained during colonoscopy). These drugs have potential side effects and must be used only and exclusively under close veterinary control with regular re-evaluations. These drugs, when used appropriately, are extremely effective.
  • Motility-modifying drugs (drugs that act on the motor activity of the intestinal tract). They are mostly used as a remedy to symptomatically alleviate the condition rather than for long-term medical management of colitis.

Until the condition stabilizes, periodic reassessment may be required. In cases of an acute episode of colitis, no follow-up may be required except for annual physical exams.

In some cases, drug administration may be necessary for months or years. It is often recommended to suspend drug therapy after a predetermined period of time, in order to determine whether mere food changes or the addition of fiber to the animal’s diet alone can control colitis. If long-term drug treatment is needed, it is advisable to determine the lowest possible dosage of the drug that can effectively control colitis.

Most dogs with colitis have a good prognosis for long-term control, particularly in cases where the underlying cause of the condition has been identified. Most infectious causes of colitis are treatable. The prognosis for colitis related to the presence of cancer depends on the type of neoplasm involved and the response to surgical or medical treatment. Patients with inflammatory colitis (lymphoplasmacytic, granulomatous or eosinophilic) appear to have the most variable clinical course. It is important that the owner of the dog suffering from chronic colitis remains in close contact with the attending veterinarian, so that appropriate changes can be made promptly for what concerns drug treatment or diet.

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