fetal bovine serum (FBS)... is derived from the blood of calf fetuses after their pregnant mothers are slaughtered by the meat or dairy industry.
I did not know this... and after reading the wiki, I found it rather disturbing...
The first stage of the production process for FBS is the harvesting of blood from the bovine fetus after the fetus is removed from the slaughtered cow. The fetus dies from the lack of oxygen by remaining in the protective environment of the uterus for a minimum of 15–20 minutes after the cow is dead...
TIL, thanks!