Severe colic is characterized by intractable pain and signs of septic shock, which is any type of loss or poor distribution of blood supply caused by bacteria or their toxins. The bacterial toxin we most commonly think about is endotoxin, so horses are usually called endotoxemic when their gum color changes, the time it takes for the capillaries of the gums to refill after pressure from a finger (called capillary refill time) increases, and the heart rate remains elevated despite treatment for pain.

However, there are many different bacteria and toxins that can trigger the same reaction.

Septic shock is the horse’s body mounting a massive immune response to bacterial toxins that, in horses with colic, have escaped from the intestine. In order to escape, the gut lining or barrier has to be broken down, and this happens when the bowel is strangulated (the intestine has become twisted or entrapped in an area of the abdomen that pinches off the blood supply).

If a horse with a strangulating obstruction of the intestine is not attended by a veterinarian and taken to surgery, it will die from the body’s response to bacterial toxins that escape from the intestine. That is why endotoxemia has been so extensively researched