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Colitis in Cats: Causes, Symptoms, and Treatment

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Lindsay Butzer, DVM
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Dr. Lindsay Butzer
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British shorthair using a litter box

Is your cat suddenly rushing to their litterbox much more than usual? Or are you noticing loose, watery stools when you scoop?

It’s not always obvious when cats are sick or in pain, but changes in their litter box habits can be a major clue when something’s amiss. Learn how to recognize signs of colitis in your cat, what can cause episodes of diarrhea, and what you can do to help soothe your feline friend’s tummy troubles.

What is Colitis in Cats?

Colitis is characterized by inflammation of the large intestine (colon). The colon is the last part of the digestive tract, and its purpose is to absorb water and electrolytes from the stool.

When the colon becomes inflamed, possibly due to parasites, a food allergy, bacteria, virus, or another health issue, it’s unable to absorb fluids properly. As a result, there will usually be diarrhea, which may be mucusy or tinged with bright red blood.

As the nerves lining the colon become irritated and sensitive, your cat may frequently feel the urge to go to the litter box, only to pass a small amount of diarrhea. Cats experiencing frequent, sometimes painful urges may also start pooping outside of their litter box.

Symptoms of Colitis in Cats

Tenesmus, the urge to defecate only to produce little or no stool

Frequently rushing to the litter box

Straining to defecate

Loose, watery stool

Stool tinged with small amounts of bright, red blood

Mucus in stool

As colitis affects the large intestine, there will not be symptoms associated with other parts of the digestive tract. The following are symptoms not typical of colitis and may indicate a different, potentially serious gastric issue.

Nausea and vomiting

Black or tarry stool can indicate bleeding in the upper digestive tract

Unexplained weight loss

Changes in appetite


What Causes Colitis in Cats?

Anything that irritates your cat’s gastric tract can manifest as colitis. The culprit can be as simple as an upset stomach due to changing foods too quickly, or it can be caused by a chronic endocrine issue like diabetes or hyperthyroidism. While acute gastric issues are common in cats, symptoms that are severe or that do not go away within a day or two should be assessed by your veterinarian as soon as possible.

Parasites are one of the most common causes of acute colitis in cats. Most of the time, you will not be able to see worms or other parasites in your cat’s stool, but they can be identified with a fecal test by your veterinarian. Your vet will need to diagnose your cat before treating a parasitic infection with one or more antibiotics or dewormers.

Dietary indiscretion, for example, after a cat has eaten trash or gorged on treats, can cause acute colitis that may clear up on its own. However, veterinary care may be necessary to rule out a more serious condition like a gastric obstruction, or to provide supportive care like antidiarrheal medication, probiotics, and/or fluids to promote recovery and prevent dehydration. Very young, older, and immunocompromised cats should be treated promptly, even in the event of mild, acute colitis.

Feline immunodeficiency virus (FIV) is known to cause chronic colitis in cats as they reach the end stages of the disease. It’s not known why so many FIV-positive cats develop recurring, chronic colitis, but one reason is likely because they are susceptible to secondary infections that cause diarrhea. Chronic inflammation of the colon lining can also be a culprit.

Food intolerances can cause colitis in cats that may clear up with dietary changes. Cats most commonly develop food intolerances to protein sources, for example, fish, beef, or chicken, though they can also be sensitive to other ingredients like starches and food additives.

Diabetes, if severe or untreated, can cause diarrhea, usually accompanied by excessive water consumption and urination, lethargy, nausea, vomiting, weight loss, and changes in appetite.

Hyperthyroidism affects 1 in 10 senior cats. Cats with hyperthyroidism often experience diarrhea, irritability, and weight loss despite increased appetite.

Kidney disease in its late stages can cause diarrhea and other systemic symptoms, typically by the time the kidneys have lost most of their waste-filtering functions. Colitis associated with severe chronic kidney disease is accompanied by weight loss, unkempt coat appearance, vomiting, and increased water consumption and urination.

Anxiety and stress stimulate the production of hormones that can cause gastric disturbances. Stressful events like travel and vet visits can cause acute colitis, though cats that suffer from chronic anxiety may have recurring stress-related gut issues.

IBD and Idiopathic Colitis in Cats

If parasites, endocrine conditions, allergies, and other potential causes have been ruled out, and your cat has not been responding to treatment, their colitis may be described as idiopathic, without a known cause. They may be diagnosed with inflammatory bowel disease (IBD).

In cats with IBD, the immune system sends inflammatory cells to the colon, as though to fight off an illness. This may be a reaction to a food or other substance, or there may be genetic factors, but there may be no known cause for your cat’s immune system to overreact.

Your veterinarian may prescribe an immunosuppressant medication to control the inflammation. They may also recommend a prescription IBD diet for cats, probiotics, and/or antibiotics to help support the gut microbiome, the part of the immune system located in the intestines.

Chronic IBD can make it difficult for the gut to absorb nutrients in food, particularly vitamins B12 and folate. Your veterinarian may check for deficiencies with a blood test and may supplement vitamin B12 with an injection.

IBD in cats is not curable, but it can be managed. Your cat may go long stretches without gut issues, especially if you keep them on a therapeutic diet as recommended by your veterinarian. Long-term use of immunosuppressant medication and other therapies may also be necessary to prevent recurring episodes of colitis.