There are a few areas on the body that provide important information regarding the state of a horse's circulatory health. These areas include the gums, the pink membrane inside the nostril, the whites of the eyes, and the pink inner vulvar membranes of mares. The simple act of evaluating the color of your horse's gums is actually a very important skill.

If instead of a healthy pink color, the gums are a dark red, "endotoxemia" is the presumed cause. Endotoxemia is a condition in which endotoxin from intestinal bacteria has entered the circulatory system, usually because of intestinal inflammation or damage. Endotoxin is a potent toxin that is part of the intestinal bacterial cell wall. Other toxins and conditions can also cause this appearance to the gums.

A dark red color of the gums usually indicates that a horse is suffering from a serious illness. You would expect to see other signs along with this, like high heart rate and slow refill time, and generally a depressed horse. If this finding is "real", then you would expect the horse to also be exhibiting other signs of illness.