The cow as a model for in vitro maturation of human oocytes

In vitro maturation (IVM), in vitro fertilization (IVF) and in vitro culture of bovine oocytes have been successfully used to produce live calves for the last 10 years. These procedures result in approximately 35% of the oocytes matured developping to the blastocyst stage. In vitro studies have shown that in vivo matured oocytes have twice the developmental potential than in vitro matured oocytes. Numerous efforts aimed to increase the oocyte's developmental competence during IVM have not been very successful. It seems that the oocytes has a pre-defined competence dependent on the the follicle of origin. We have shown that medium to large-sized follicles in the early phases of atresia contain competent oocytes, while many actively growing follicles contain incompetent oocytes. Our conclusions are that an early atresia phase or an artificial plateau in the follicular growth may mimic the conditions present during the pre-ovulatory stages of follicular maturation, which lead to oocyte competence.