Circulatory system of the horse capacity of the muscular system far exceeds the capacity of the cardiovascular system to deliver oxygen. Blood is made up of red blood cells (erythrocytes) and white blood cells (leukocytes), as well as plasma. Produced in bone marrow, red blood cells are responsible for carrying oxygen to tissue and removing carbon dioxide, all via hemoglobin. White blood cells are used for defense against pathogens in the immune system. Plasma suspends the blood cells, contains clotting factors, and contributes to the greatest volume of blood. The heart and blood vessels contain approximately of blood in a horse, which equates to about
Red blood cell loss, such as prior to an operation. Before blood is given, a small sample of the recipient's blood is tested with the transfusion in a process known as cross-matching. In addition to the transmission of infection, certain types of transfusion reaction. In 2008 it was reported that human embryonic stem cells had been successfully coaxed into becoming red blood cells in the lab. The difficult step was to induce the cells to eject their nucleus; this was achieved by growing the cells on stromal cells from the bone marrow. It is hoped that these artificial red blood cells can eventually