A  Horses do in fact have a spleen, so you win that part of the bet. However, although some aspects of the anatomy and function of the horse’s spleen are different from the human spleen, these physical and functional characteristics are shared by a number of other mammals.

First of all, what is the spleen, and what function does it serve in the body? The spleen is a dense, red-colored structure that is situated high on the left side of the abdomen, lying against the rib cage. A ligament (called the nephrosplenic ligament) connects the spleen to the left kidney. In all species, one of the primary functions of the spleen is in the formation and filtration of blood. However, the bone marrow is the primary site for blood formation and normally the spleen does not produce new red blood cells. On the other hand, the spleen throughout life is one of the body’s organs that produces lymphocytes, a type of white blood cell that is extremely important in immune function.

The filtration of blood by the spleen is important in the removal of foreign materials (including bacteria) and old blood cells. Blood cells, particularly the red blood cells, have a fairly short lifespan, and it is the job of the spleen to recognize and remove old and degenerating cells from the circulation