Therefore, the increase in blood volume associated with splenic contraction provides a tremendous boost in the horse's capacity to transport oxygen. Indeed, this high capacity for oxygen transport contributes to the high athleticism of the horse. We know this to be true because following removal of the spleen, horses suffer a sharp decline in athletic ability. Splenic contraction and release of stored red cells can occur under other circumstances, for example when the horse is excited. Despite this, many racehorse trainers routinely use such resting measurements as a guide to the fitness of their horses.
Medical problems involving the spleen are fairly uncommon.
However, splenic rupture and hemorrhage can occur when the horse receives a kick from another horse to the left abdominal wall. Although the spleen is partially protected by the rib cage in this region, a heavy blow can cause severe injury and hemorrhage into the abdominal cavity. In the worst-case scenario, the horse will die from the acute hemorrhage. More commonly, the bleeding is self-limiting and goes undetected. In other cases, the horse might show signs of mild to moderate colic.