Obesity is reported as present in 51% of adult horses in the United States. Insulin dysregulation and endocrinopathic laminitis are risk factors associated with obesity.
A study at Michigan State University’s College of Veterinary Medicine investigated the effects of body condition on intestinal permeability in 13 horses [Kopper, J.J.; Travers, J.L.; Schott, H.C.; Cook, V.L. Effect of body condition on intestinal permeability in horses. American Journal of Veterinary Research, August 2019, vol. 80, no. 8; pp. 792-798].
The study horses, ranging in age from 8-15 years, were destined to be euthanized for non-intestinal related problems. They had no history of gastrointestinal disease and no treatment with NSAIDs or antimicrobials within the preceding 30 days. Seven of the horses were obese with body condition scores (BCS) of 7-9. The other six horses were lean with BCS 4-5. Glucose and insulin were measured with an oral sugar test and other corroborating testing procedures. After a two-week dietary acclimatization period of unlimited grass hay but no concentrates, the horses were euthanized. Portions of each segment of bowel were obtained for histopathology and measurement of lipopolysaccharide (LPS) flux across the mucosa.
LPS flux across the jejunal mucosa was significantly greater in obese than lean horses, indicative of increased intestinal permeability possibly due to alterations in tight junction proteins. Obesity might have an effect on increasing adipose-derived inflammatory cytokines and that, in turn, could alter tight junctions and paracellular transport across the intestinal barrier.
It is also known that gastrointestinal microbiota diversity is different between obese and lean horses, particularly when caused by differences in diet. Microbiota also have effects on the integrity of tight junctions.
There were no differences in LPS flux across the mucosa of the ileum, cecum, right dorsal colon or rectum of obese or lean horses or between horses with or without insulin dysregulation. Histologically, villus height and width or surface area of jejunum and ileum were similar in obese and lean horses. And, interstitial-to-crypt ratios for cecum, pelvic flexure, right dorsal colon and rectum were similar between obese and lean horses.
Human studies have revealed that obesity is associated with more than 20 medical conditions and co-morbidities. In this study, five of the seven obese horses and one of the six lean horses suffered from insulin dysregulation.
In conclusion, obese horses might be at increased risk from greater systemic absorption of LPS due to increased jejunal permeability.