MODEL RELEASED. Animal biotechnology. Embryologist removing cow ovarian follicles from a petri dish as part of an in vitro fertilisation (IVF) technique. Each of these cow follicles contain a single immature egg or oocyte. The oocytes are placed in a special fluid medium and then fertilised by sperm. After fertilisation, the resulting embryo is placed in a culture until it reaches the blastocyst stage which contains about 100 cells. The blastocyst is placed in the womb (uterus) of a cow, where it implants to cause a pregnancy. This technique is used with a number of species for spreading favourable genes.