Fetal bovine serum (FBS) is the most widely used growth supplement for cell culture media because of its high content of embryonic growth promoting factors. When used at appropriate concentrations it supplies many defined and undefined components that have been shown to satisfy specific metabolic requirements for the culture of cells - See more at: http://www.sigmaaldrich.com/life-science/cell-culture/cell-culture-products.html?TablePage=9628642#sthash.FL0JFxAr.dpuf