“…In order to complete nuclear as well as cytoplasmic maturation in an in vitro culture system, several components such as follicle stimulating hormone, luteinizing hormone, estradiol, the presence of cumulus cells and a serum source must all be considered. Maturation of oocytes for in vitro fertilization (IVF) has been accomplished in culture medium supplemented with estrous cow serum (ECS) (Lu et al, 1987(Lu et al, ,1988, fetal bovine serum (FBS) (Goto et al, 1988;Zhang et al, 1991), as well as in either gonadotropin and steroid supplemented ECS or FBS (Sirard et al, 1988;Younis et al, 1989;Schellander et al, 1991;Threlfall, 1989, 1990). After IVF, embryo co-culture with cumulus cells (Kajihara et al, 19901, granulosa cells (Yang and Lu, 19901, and oviduct cells (Eyestone and First, 1989) have been used to provide the necessary culture environment so that embryos may develop to advanced preimplantation stages for eventual nonsurgical transfer to recipients and/or cryopreservation for storage.…”