The Horse’s Spleen: Aid to Exercise

The role of a horse’s red blood cells is to carry oxygen to active muscle cells. In the relaxed horse, not all red blood cells are in use. Extra cells (about 30% of the total) are stored in the spleen, a large organ located in the horse’s abdominal cavity between the left kidney and the small colon. When the horse performs strenuous exercise, the spleen contracts, pushing these extra red blood cells into circulation and thus greatly increasing the oxygen-carrying capacity of the blood.

Almost all vertebrate animals, including humans, have a spleen. This organ is not essential to life, and if it is removed because of damage or disease, most animals can get along well. Removal of the spleen may be necessary if it is ruptured by a kick, fall, or other trauma. Splenic rupture causes internal bleeding and shock that can be life-threatening if not controlled. While horses can survive without a spleen, their athletic ability will be significantly reduced.