Colitis in dogs: symptoms and treatment

Overview

A healthy colon absorbs water and salts from intestinal contents. It also stores faeces until defaecation. Inflammation reduces water absorption, softening faeces. The inflamed bowel reacts more readily to stretching, which can cause a sudden urge to defaecate.

Acute colitis may begin as a single diarrhoea episode. Colitis lasting at least three weeks is considered chronic. Lymphocytes and plasma cells may accumulate in the mucosa during persistent disease. Lymphoplasmacytic colitis, dominated by these cells, is more common than forms dominated by eosinophils or neutrophils.

In a UK primary-care sample in 2016, colitis was recorded in 155 dogs, or 0.69%. Dogs in the sample attended 784 practices.

Colonic inflammation alters contractions so faeces move towards the rectum more quickly. Colonic bacteria feed on some carbohydrates not digested in the small intestine.

Causes

Common factors irritating the colon

Stress can trigger large-bowel symptoms. Whipworms can cause large-bowel diarrhoea. Salmonella infection can cause enteritis and bloody diarrhoea. A dietary protein may trigger food-allergic colitis. In persistent inflammation, intestinal immune defences may react excessively to microbes in the bowel contents.

Mucosal damage can expose immune cells in the bowel wall to foreign substances in the contents. Inflammation can increase mucus secretion by goblet cells. Rare pseudomembranous colitis is associated with Clostridioides difficile infection. The precise initial cause remains unclear in many cases.

Granulomatous colitis

In granulomatous colitis, particular Escherichia coli bacteria invade the colonic wall. They can multiply inside mucosal macrophages, cells that engulf material.

Risk factors

Colitis is often diagnosed in middle-aged dogs. Granulomatous colitis particularly affects young Boxers and French Bulldogs. Its symptoms often begin before four years old. Animals developing eosinophilic colitis are often younger than usual.

Changing food too quickly can trigger diarrhoea. Raw or undercooked food can expose dogs to Salmonella. An antibiotic altering intestinal microbes can predispose to rare C. difficile-associated colitis.

Symptoms may begin after eating contaminated food. Contaminated drinking water can carry Salmonella into the intestine.

Typical symptoms

Individual bowel movements are usually small despite frequent defaecation. Symptoms can ease and then worsen again.

• An urgent need to go outside because the urge comes suddenly.
• Remaining crouched and straining after defaecation.
• Mucus on or within faeces.
• A small amount of bright-red blood towards the end of defaecation.
• Sometimes, painful defaecation.

Marked weight loss is more common if the small intestine is also affected. Granulomatous colitis can involve weight loss even when large-bowel diarrhoea is the most visible symptom. Vomiting occurs in fewer than one-third of dogs with colitis.

Markedly increased defaecation frequency more often suggests disease in the large intestine than the small intestine. Small-bowel diarrhoea may instead involve larger volumes at each bowel movement.

Complications and consequences

Ulcers can develop in the inflamed mucosa. Persistent colitis can cause scarring in the bowel wall. Extensive scarring worsens the outlook for chronic colitis. Granulomatous inflammation can thicken the wall enough to narrow the lumen.

Rare C. difficile-associated colitis can cause severe dehydration. In severe disease, circulating fluid volume can fall enough to cause shock. Chronic colitis symptoms can return after an initial treatment response.

Continued profuse diarrhoea causes faecal fluid loss and can dehydrate the dog. Concurrent vomiting can accelerate dehydration. Dehydration can disturb electrolyte balance.

In severe salmonellosis, bacteria can cross the intestine into the bloodstream. A dog can shed Salmonella for weeks after symptoms end.

Diagnosis at the vet

History, palpation and samples

The vet establishes symptom onset, duration and severity before choosing tests. Rectal palpation may reveal a polyp causing colitis-like symptoms. Faecal flotation, a laboratory method separating eggs, can look for whipworm eggs. Shedding is intermittent, so one negative sample does not always exclude infection.

If Salmonella is suspected, bacterial culture of diarrhoeic faeces is the first-choice test. Blood and urine tests help investigate other diseases with persistent symptoms. Blood results can be normal even in chronic colitis. The vet may also investigate hypoadrenocorticism, or Addison's disease.

Blood eosinophils can increase in both eosinophilic colitis and parasitic infection.

Imaging and colonoscopy

Contrast imaging can sometimes reveal a narrowed bowel segment.

Abdominal ultrasound examines the colonic wall and looks for local lesions. It can also assess nearby lymph node size. Persistent large-bowel diarrhoea despite appropriate treatment trials may prompt endoscopy. Colonoscopy is performed under general anaesthesia. The colon is emptied beforehand because faeces can conceal small mucosal lesions. Biopsies are taken from different colonic areas even if the surface looks normal.

Mucosa appearing fragile on endoscopy may also be abnormal microscopically. Tissue samples can distinguish inflammation from an intestinal tumour. FISH testing can locate E. coli in inflamed mucosa if granulomatous colitis is suspected. Susceptibility testing of bacteria isolated from the biopsy then helps select an antibiotic.

If a lesion is beyond the endoscope's reach, a surgical biopsy may sometimes be needed. Very low blood albumin can affect suitability for anaesthesia and the fasting required for preparation.

With marked weight loss or poor appetite, endoscopy may also examine the end of the small intestine.

Treatment

Supportive care and diet

The vet prescribes treatment according to symptom severity and the identified cause. A dehydrated dog may need fluids. Supportive care can begin in a severely affected dog while the cause is investigated. A stable patient may have a dietary trial of at least two weeks, eating only the selected food.

Fibre such as psyllium can bind free water in faeces. Colonic bacteria convert some fibre into short-chain fatty acids used for energy by surface cells. Some dogs may do better on a low-fibre diet. If food hypersensitivity is suspected, a diet with proteins broken into smaller pieces may be tried.

Most dogs with stress colitis return to normal within three to five days. A well-chosen diet can help control chronic colitis.

If the first diet does not help and the dog remains stable, another with a different composition may be considered. In an open follow-up of 37 dogs, highly digestible food and soluble fibre gave good or excellent relief of chronic large-bowel diarrhoea. With hydrolysed food, breaking down protein aims to reduce the immune response. If diet gives partial relief, the most effective food can continue alongside other treatment.

Medication depends on the cause and condition

Mild acute bloody diarrhoea is generally treated without antibiotics when general health is good and there is no dehydration. Antibiotics may be needed if severe disease causes general symptoms persisting despite adequate fluids. With strong suspicion of whipworms, parasite treatment may be considered despite a negative egg examination. For confirmed E. coli-associated granulomatous colitis, the antibiotic is selected from susceptibility testing of bacteria isolated from a bowel biopsy.

Eosinophilic colitis treatment may combine diet with an anti-inflammatory glucocorticoid. Chronic inflammation may need immunosuppressive medication if dietary treatment is insufficient.

Laboratory susceptibility does not always mean the same medicine will work against inflammation within the bowel wall. Infectious causes are investigated before medication suppressing intestinal immune defences begins. Antibiotics are not usually started for acute diarrhoea when general symptoms resolve with fluids.

Prevention

Change foods gradually because a rapid switch can trigger diarrhoea. Thoroughly cooking poultry reduces Salmonella risk. Use separate chopping boards for canine raw food and human food. Do not let dogs eat dead birds, which can carry Salmonella.

Collect faeces from a Salmonella-shedding dog to reduce environmental bacteria. With food hypersensitivity, remove the triggering ingredient.

Wash food and water bowls because bacteria can survive on their surfaces. With confirmed Salmonella, careful handwashing after faeces collection reduces human exposure.

Important for dog owners

Keep fresh water continually available during diarrhoea. Provide more frequent outings if your dog urgently needs to defaecate. Record bowel movement frequency and stool consistency for the vet. Mention appetite changes and weight loss too.

Do not give human anti-diarrhoeal medication without veterinary advice. Contact a vet if mild diarrhoea in an otherwise well dog does not improve within 48–72 hours. Even proteins in treats can interfere with dietary trial interpretation.

Listing previous treats helps select a genuinely novel protein for a trial. Contact a vet about fresh blood in faeces even if your dog still eats normally.

Bring a current medication list because it forms part of investigating intestinal symptoms.

Frequently asked questions

What does large-bowel diarrhoea usually look like?

A dog may defaecate frequently but pass only a small amount each time. Faeces may contain mucus and small amounts of fresh blood. Straining can continue after faeces have passed.

How quickly can stress colitis improve?

Most affected dogs return to normal within three to five days. Recurrent large-bowel diarrhoea sometimes needs tests for other causes, such as a polyp. Rapid deterioration or profuse bloody diarrhoea needs emergency assessment.

Does colitis always need an antibiotic?

Mild acute bloody diarrhoea in a well dog is generally treated without antibiotics if there is no dehydration or general illness. In confirmed granulomatous colitis, an antibiotic can be chosen according to susceptibility of bacteria from the bowel biopsy. Adequate fluids can correct general symptoms caused by fluid loss.

Does fibre help every dog with colitis?

Some dogs with chronic colitis benefit from fibre binding water in bowel contents. Others do better with low-fibre food. The vet chooses a trial food according to previous feeding and symptoms.

Why are colonic biopsies taken?

Biopsies from different colonic sites identify inflammatory cells in the mucosa. They can help distinguish colitis from a tumour with similar symptoms. If granulomatous colitis is suspected, tissue can be examined for bacteria within the mucosa.