Inflammatory bowel disease (IBD) involves chronic inflammation of the gastrointestinal (GI) tract. In humans, there are 2 major forms of IBD: Ulcerative Colitis (UC) and Crohn’s Disease. While both are characterized by chronic inflammation they differ in which tissue layers are affected and the location and continuity of inflammation. In cats and dogs, IBD tends to be less severe than in humans. Especially in cats, the clinical picture can be influenced by concurrent disease (e.g. IBD, cholangitis, and pancreatitis, called “triaditis”). Dogs suffer from colitis more frequently than cats, where the disease mainly involves the small intestine (SI). Horses have a collection of diseases classified as IBD but separated by type, extent, location, and inflammatory cell infiltrate: lymphocytic-plasmacytic enterocolitis (LPE), granulomatous enteritis (GE), idiopathic focal eosinophilic enterocolitis (IFEE), and multisystemic eosinophilic epitheliotropic disease (MEED).  

Similarities in humans

IBD in humans, both Crohn’s and UC, often develops in the late teenage to young adult years although it can appear at any age. In cats, IBD is most often diagnosed in middle-aged and older cats although it too may be found at any age. IBD is most prevalent in younger horses, although LPE and MEED are frequently found in older horses. Similarities exist in histopathology seen in GE in horses and Crohn's disease in people.  In all species, IBD seems to be caused an abnormal immunologic response to dietary antigens or bacteria in patients who are susceptible because of any number of genetic abnormalities.


Differences in humans

IBD in humans can be very painful and debilitating and can sometimes lead to life-threatening complications.  In small animals these are rare unless the IBD is severe and chronic enough to be categorized as a “protein-losing enteropathy” (protein loss due to compromised GI mucosa). In this case, patients are at some risk for developing blood clots, emboli, or ascites (abdominal swelling due to the accumulation of fluid in the peritoneal cavity). Typically, IBD in small animals is a chronic, slowly-progressive disease and not as painful or debilitating as seen in humans.

Disease etiology

The cause of IBD is multifactorial and poorly understood. Previously it was thought that diet and stress were primary causes of the disease, but these are now recognized as risk factors that aggravate the condition. Researchers now recognize an immune system malfunction as the main culprit. Similar to the autoimmune reaction seen with an allergic response, an abnormal immune response leads to the lining of the intestine being invaded by inflammatory cells. This results in the loss or destruction of normal GI cell numbers and function, resulting in intestinal villi atrophy and an inability to digest and absorb nutrients.

Clinical presentation

Significant weight loss and chronic diarrhea are typical clinical signs of IBD in animals. Rectal bleeding may be present in canine large bowel disease but is rarely seen in cats. Since various parts of the GI tract can be affected in cats, clinical presentation may vary depending on severity and location of the inflammation: inflammation in the colon results in chronic large bowel diarrhea and may include blood in the stool whereas chronic vomiting can occur if the stomach or areas of the small intestine are affected. In horses, diarrhea may or may not be present, and weight loss is primarily present in GE, LPE, and MEED. Horses with IFEE primarily suffer from colic or abdominal pain as focal inflammatory lesions cause narrowing of the intestinal lumen and obstruct the flow of ingesta. Hypoproteinemia and generalized skin disease can also be symptoms of equine IBD. Typical IBD symptoms in humans include severe and chronic diarrhea, abdominal pain, rectal bleeding, fatigue, and weight loss; symptoms vary due to severity and location of inflammation.


In both humans and animals treatment involves the use of anti-inflammatory and immunomodulating drugs. Antibiotics may also be prescribed for anti-inflammatory effects and to “reset” the microbiome (when paired along with a probiotic). Natural supplements and remedies include dietary changes, vitamin B12, calcium, and vitamin D. IBD in small animals is often treated with a hypoallergenic or hydrolyzed diet to reduce antigenic stimulation of the immune system (fiber would be added to this diet in cases of large bowel diarrhea, i.e. colitis). In severe cases, treatment of IBD in human patients involves surgical procedures.  The severity of IBD and the fact that many affected human and animal patients continue to have symptoms despite or because of current available therapies demonstrates a strong need for increased understanding and novel treatment approaches for the disease.