Fetal bovine serum (FBS) is derived from the blood drawn from a bovine fetus via a closed system of collection at the slaughterhouse. Although fetal bovine serum has cells and clotting factors removed, over a thousand components conducive to cell growth remain, including: Attachment factors, growth factors, hormones, lipids, spreading factors, sugars, transport proteins, bovine serum albumin, vitamins etc. The globular protein, bovine serum albumin (BSA), is a major component of fetal bovine serum. The rich variety of proteins in fetal bovine serum maintains cultured cells in a medium in which they can survive, grow, and divide.