Certificates of Analysis vary between commercial suppliers, but each usually includes the following details: filtration statement, country of blood collection, country of manufacture, cell growth performance testing, microbial sterility testing, as well as screening for mycoplasma and virus, endotoxin, hemoglobin, IgG gamma glutamyl transferase and total protein assays. FBS may also be tested for country of collection. Ethics Ethical questions have been raised regarding the blood collection process due to the potential suffering caused to the fetus. There has been discussion concerning the methodologies for the collection of fetal bovine serum. The International Serum Industry Association (ISIA) has published literature providing detail on the extensive regulation and processes employed to ensure that serum is collected in an ethical manner. Although the act of slaughter of the dam and the time which passes in the slaughter process prior to harvesting will induce unconsciousness or death of the fetus prior to serum harvesting, it has been postulated that exposure of live unborn calves to oxygen could cause them to gain awareness before being killed, resulting in active debate about the ethics of harvesting serum. While the Industry Association accepts that certain organizations have concerns, they maintain that all collections of serum take place under veterinary supervision in registered slaughterhouses controlled by the competent authority in the country of collection, making such an issue extremely unlikely. Serum use Fetal bovine serum is commercially available from many manufacturers, and because cells grown in vitro are highly sensitive, customers usually test specific batches to check for suitability for their specific cell type. When changing from batch to batch it is usual to adapt the cells to the new batch of material, for example, by mixing 50% of the old serum with 50% of the new serum and allowing the cells to acclimatize to the new material. Serum is stored frozen to preserve the stability of components such as growth factors. When serum is thawed, some precipitation may be seen. This is a normal phenomenon, and it does not compromise the quality of serum in any way. The precipitate may be removed by transferring the serum to sterile tubes and centrifuging for 5 minutes at 400 × g. To limit the amount of precipitation, it is recommended that the serum is thawed in a refrigerator at 2-8˚C. The serum should be regularly stirred during this process. Repeated freeze/thaw cycles should be avoided, and it is advisable