Page 103 - October 2023

VETERINARY VIEWS
Gastrointestinal disease
in the horse takes many forms,
ranging from loss of appetite to diarrhea
to colic to colitis or inflammation of small intestine.
the inflammatory response might start in
one tissue, other body tissues are affected. Enterocytes are especially sensitive to
small changes from stress, colic, disease, medications, and diet. The microbiome is affected by abrupt dietary changes, excessive carbohydrate ingestion, systemic antimicrobial administration, and colic. The intestinal response to these situations and immune system responses plays a critical role in the development of systemic inflammation.
Hunger, caused by restricted feeding protocols such as only being fed two meals
a day, is a psychological stress that increases cortisol, which is damaging to intestinal epithelium to cause leaky gut syndrome.
Free choice access to forage can mitigate this psychological stress. However, for horses suffering from obesity and/or equine metabolic syndrome, it may not be possible to feed as much hay as the horse will eat.
Horses with varying body condition scores, even those not suffering from obesity, can develop leaky gut syndrome. Consumption of high-starch feeds (grains) results in acidosis and opening of intestinal tight junctions. Lipopolysaccharide (endotoxin) from bacterial death in the
face of acidosis then can migrate from the intestines to the bloodstream. This signals the immune system to increase production of cytokines to mount an immune defense that is accompanied by inflammation. Obese horses are particularly at risk because they start with higher levels of systemic inflammation that is exacerbated by hormonal reactions to consumption of high- starch feed.
Strenuous or intense exercise pulls blood away from the intestinal tract to privileged organs such as the brain and kidneys. Reduced intestinal blood flow reduces oxygen to the
intestinal lining, resulting in enterocyte cell injury and loss of tight junctions. Reperfusion of ischemic (poorly oxygenated) tissue increases reactive oxygen species that further injure intestinal barrier function.
Constriction of the circulation of visceral organs is a normal physiologic response to heat stress. This response helps to expand blood flow to the skin and muscles to dissipate internal heat and for locomotion. High internal temperature along with reduced gastrointestinal blood flow creates tissue hypoxia, acidosis, ATP (energy) depletion
and oxidative stress – these conditions disrupt the intestinal barrier and tight junctions. Gastrointestinal permeability also increases in the face of dehydration due to reduced intestinal blood flow.
Intestinal pathogens or mycotoxins that bind to intestinal cell surfaces have the potential to adversely alter the integrity of
Constriction of the circulation of visceral organs is a normal physiologic response to heat stress. This response helps to expand blood flow to the skin and muscles to dissipate internal heat and for locomotion.
SPEEDHORSE October 2023 101
Hunger, caused by restricted
feeding protocols such as only being fed two meals a day, is a psychological stress that increases cortisol, causing leaky gut syndrome.
Intense exercise pulls blood away from the intestinal tract to other organs such as the brain and kidneys. Reduced intestinal blood flow reduces oxygen to the intestinal lining, resulting in intestinal lining cell injury and loss of tight junctions.