Equine Colic: a Real Pain in the Gut - Response to Injury

Response to Injury
The pathophysiologic events that take place during an acute abdominal crisis may include bowel distention, bowel ischemia, tissue reperfusion, necrosis, inflam- mation, apoptosis and changes in bacterial flora. The responses to these events include changes in intestinal motility, water and electrolyte secretion-absorption, vascular permeability, inflammatory cell activation, and ultimately tissue structure. Colic (the clinical signs caused by abdominal pain) is initiated by stimulation of nervous reflexes and formation of chemical mediators that cause an increase in heart rate, pooling of blood, fluid sequestration, and alterations in tissue perfusion and oxygenation. Understanding the clinical signs created by these physiologic alterations helps the veterinarian determine the type of disease and its severity.

When a horse’s diet is changed from strictly forage to a diet with both forage and concentrate, there is an increase in dry matter content of ingesta in the right dorsal colon and evidence of increased gas production within 48 hours (1). The decrease in water content is likely due to a decrease in fiber content and an increase in soluble carbohydrate consumption, which also increases gas production.1 This suggests a systemic response to changes in a horse’s diet, particularly when adding soluble carbohydrate in the form of grain.

Intestinal blockage alters intestinal motility, distends the intestine, initiates secretion of fluid into the intestinal lumen, and eventually causes mucosal injury. Ischemia due to strangulation of mesenteric vessels rapidly results in cellular damage throughout the bowel wall especially within the mucosa and serosa. The diseases that produce these effects are categorized as obstruction (simple obstruction), strangulation obstruction, (hemorrhagic strangulation obstruction and ischemic strangulation obstruction), and nonstrangulation infarction, which in the horse is synonymous with thromboembolic colic. [...]