The number of blood groups varies between the domestic species and are determined by the presence of antigenic components on the surface of the [[Erythrocytes|red blood cells]]. Cattle have the most complex blood group systems while cats are quite simple. | The number of blood groups varies between the domestic species and are determined by the presence of antigenic components on the surface of the [[Erythrocytes|red blood cells]]. Cattle have the most complex blood group systems while cats are quite simple. |