Biology is complex, and there are lots of additional factors required for cell metabolism and growth.  Classically, researchers have used animal serum as an easy work-around to delivering these factors to cells.  The animal serum of choice is usually fetal bovine serum (FBS), although horse serum, chick embryo extract, or other sera types are sometimes used.  FBS [27] is, as the name might suggest, derived from fetal calves which are by-products of the dairy industry.  The process involves sterile collection of the blood, coagulation, and centrifugation to remove clotting factors and blood cells, followed by filtration before being available for sale.  FBS contains a variety of growth factors, hormones, and necessary components for cell survival (Figure 7).  In sum, it’s not the most “animal friendly” product imaginable.  In skeletal muscle, it helps cells to proliferate and survive and the reduction of serum from 10% to 2% in medium formulations promotes the fusion of skeletal myotubes.  However, if the purpose of in vitro meat is to eliminate animals from the process altogether while catering to moral imperatives, vegetarians, and vegans alike, then serum-free medium formulations need to be used.