Inflammatory Bowel Disease in Horses: What You Need to Know

Inflammatory bowel disease (IBD) is an umbrella term used to describe various types of intestinal disease in which inflammatory cells infiltrate the walls of the gastrointestinal tract. All horses falling under this umbrella show similar clinical signs.

“We don’t fully understand how or why IBD develops in horses, so devising a treatment plan can be challenging. Research examining the mechanism of how the different types of IBD develop could prove useful in coming up with effective targeted treatments,” explained Ashley Fowler, Ph.D., a Kentucky Equine Research nutritionist.

Diagnosing IBD

Clinical signs. According to a recent study published by Kranenburg and coworkers, IBD is diagnosed in approximately 32.5% of horses with unexplained weight loss, making it a common condition.^* In addition to weight loss in horses with a good appetite, signs of IBD include:

• Ventral edema (swelling under the abdomen);
• Diarrhea;
• Lethargy;
• A sensitive abdomen;
• Colic or recurrent colic; and
• Reduced performance.

Thickened loops of small intestine via rectal palpation or abdominal ultrasound examination support the diagnosis of IBD.

Biopsy. Definitive diagnosis of IBD and subsequent characterization of type requires intestinal biopsy. Preferably, biopsies are taken via endoscopy from the small intestine rather than the large intestine.

Biopsies will identify one of four different types of IBD, or even a combination of the four. One type of IBD is granulomatous erythema, which is similar to Crohn’s disease in humans. Another form, lymphocytic-plasmacytic enterocolitis (LPE) was once thought to be the least common form of IBD; however, recent reports suggest it is more prevalent than historically believed. Researchers reported that 78.5% of 149 cases of IBD were the LPE form.

Intestinal Function

Kranenburg and colleagues also found that horses with IBD had impaired oral glucose absorption test results.

“This test helps diagnose small intestinal malabsorption. After administering a specific amount of glucose by nasogastric tube, changes in blood glucose levels are measured. Partial malabsorption is indicated if blood glucose fails to increase by at least 85% of baseline values, and total malabsorption is indicated if they increase by less than 50%,” described Fowler.

Fifty-four horses diagnosed with IBD in this study underwent an oral glucose absorption test. Almost three-quarters of the tested horses were classified as having partial malabsorption. No horses suffered total malabsorption.

Horses with IBD can also have low blood protein levels (hypoproteinemia) due to the decreased absorptive capacity of the small intestine. This occurs due to the abnormal presence of the cellular infiltrates, such as the lymphocytes and plasmacytes, in the wall of the small intestine. The researchers found that 11% of the 113 tested IBD horses had hypoproteinemia.

Treatment

 Because IBD is considered an inflammatory condition, affected horses are often treated with corticosteroids. Indeed, the horses included in Kranenburg’s study were often prescribed four to six weeks of corticosteroids, usually oral prednisolone. In addition, diet changes were sometimes instituted; however, specific details regarding those diet changes were not proffered.

“One of the goals of feeding horses with IBD is to improve nutrient absorption. In some cases, absorption can be improved by feeding smaller, more frequent meals throughout the day. If a horse is having an inflammatory reaction to an ingredient in the diet, an elimination diet may help identify the inciting ingredient. Horse owners should work with a nutritionist to ensure that caloric needs are still being met for horses with IBD who are fed an elimination diet,” advised Fowler.

Outcome

Horses included in the study by Kranenburg were followed for six weeks after being diagnosed with IBD. Of the 140 horses available for follow-up, 100 (71%) showed an improvement in clinical signs.

Data from 62 of the horses were available one year after diagnosing IBD. Thirty-two (52%) were still alive, but 20 (32%) had been euthanized for reasons related to IBD.

“The likelihood of survival at one year was significantly greater for horses that had improved after six weeks than for those that had not improved clinically at six weeks,” reported Kranenburg.

“Thus, improvement after six weeks could be used as a predictor of survival at one year,” explained Fowler.

Potential Link to EGUS

Kranenburg and coworkers suggested that horses with IBD may also suffer from equine gastric ulcer syndrome (EGUS), particularly the glandular form. Little research, however, has been performed to confirm or refute this association. In the current study, 78 of the 149 horses (52%) were diagnosed with squamous disease, whereas 89 of 146 horses (61%) had glandular disease. However, no further discussion on the relationship between EGUS and IBD was presented; further research is needed.

“Similar to IBD, we don’t fully understand the causes of glandular gastric disease. Some research suggests that glandular disease has an inflammatory component, with one study reporting a positive relationship between glandular and duodenal lymphoplasmacytic inflammation scores,” Fowler said.^**

Conclusion

The predominant form of IBD in this study was LPE, which differs from previous reports, suggesting that granulomatous enteritis (similar to Crohn’s disease in humans) was the most common. Affected horses show evidence of malabsorption based on the presence of hypoproteinemia, as well as impaired glucose absorption. Horses with improved clinical signs six weeks after diagnosis were more likely to be alive one-year post-diagnosis.

Kentucky Equine Research maintains a roster of research-proven digestive health products that might be appropriate for horses with inflammatory conditions of the gastrointestinal tract. Consult with your veterinarian or an equine nutritionist to select an appropriate supplement to complement medical therapy.

Further, EO-3, a marine-derived oil rich in the long-chain polyunsaturated fatty acids EPA and DHA, has anti-inflammatory activity and is also appropriate for horses with IBD.^***

^*Kranenburg, L.C., B.F. Bouwmeester, and R. van den Boom. 2024. Findings and prognosis in 149 horses with histological changes compatible with inflammatory bowel disease. Animals (Basel) 14(11):1638.

 ^**Banse, H.E., F. Del Piero, F.M. Andrews, N. Garcia-Abarca, and T.T.N. Watanabe. 2023. Characterization of gastrointestinal inflammatory cell type in equine glandular gastric disease. American Journal of Veterinary Research: doi.org/10.2460/ajvr.23.06.0129.

 ^***Marton, L.T., R.A. Goulart, A.C.A. Carvalho, and S.M. Barbalho. 2019. Omega fatty acids and inflammatory bowel diseases: An overview. International Journal of Molecular Sciences 20(19):4851.