A routine part of many horses’ lives involves both travel and exercise as owners engage in their equestrian pursuits. A study at the University of Guelph in Canada analyzed the effects of transport and exercise on intestinal permeability and systemic inflammation in horses [McBilloway, M.; Manley, S.; Aho, A.; et al. The combination of trailer transport and exercise increases gastrointestinal permeability and markers of systemic inflammation in horses. Equine Veterinary Journal Sept 2022; DOI: 10.1111/evj.13888].
The cross-over study took place from Jan 18 – May 13, 2021, with at least seven days separating treatments. Eight mature mares used in the study were stomach tubed with a contrast agent, iohexol, as a gastrointestinal permeability tracer. Then, four horses were assigned to one hour of trailer transport. That was followed by 30 minutes of moderate exercise on a free lunge in an indoor arena at heart rates of 150 bpm. The other four sedentary horses with no travel served as controls. Plasma samples were taken prior to administration of the GI tracer. They were taken again following transport and following exercise. Finally, plasma samples were taken 1, 2, 4 and 8 hours after exercise.
The plasma samples were evaluated for inflammatory biomarkers (SAA, LPS, lipopolysaccharide-binding protein, and intestinal fatty acid binding protein) and tight junction protein. Feces—prior to loading, during or immediately after transport, and the first feces following exercise—were also evaluated for tight junction protein (zonulin).
Leakage through weakened tight junctions of the intestinal epithelium causes “leaky gut syndrome.” Pathogens and other inflammatory substances enter the circulation and then trigger systemic inflammatory conditions. An affected horse might experience impaired skeletal muscle metabolism, metabolic dysfunction, allergies and/or arthritis.
Results from the horses undergoing transport and exercise demonstrated that there was a marked increase in intestinal permeability. This was especially true compared to the control sedentary horses. Additionally, inflammatory markers were elevated in the transport/exercised horses. Markers of intestinal permeability and systemic inflammation were persistently elevated for up to six hours following transport and exercise.
The authors summarize, “Whilst our combined stress test produced a clear increase in gastrointestinal permeability, analysis of zonulin both in plasma and feces indicates that a decline in function of this tight junction protein was not a major contributor. There are many other possible explanations for the increase in gastrointestinal permeability, including decline in function of other tight junction proteins (such as claudin and occludin), ischemic injury to mucus-producing cells, and/or acute stress-induced disturbance of the gastrointestinal microbiome.” The bottom line is that transport and exercise can contribute to leaky gut syndrome and systemic inflammation.