Approaches to in vitro oocyte growth in domestic farm mammals: how and why?

Unlocking the developmental potential of oocytes at various stages of folliculogenesis represents a major challenge in reproductive biology and assisted reproductive technologies. While in vitro maturation (IVM) of fully grown oocytes is widely applied, the vast majority of oocytes enclosed within early-stage follicles remain underutilized. This review outlines current advancements in in vitro culture systems designed to support oocyte growth and differentiation, with particular attention to the contributions of the authors. Key developments, mainly encompassing the bovine species, include the use of prematuration strategies to enhance the competence of oocytes retrieved from antral follicles, stepwise in vitro culture protocols for growing oocytes from early antral follicles, and efforts to establish defined systems for preantral follicle culture. Emerging insights into chromatin dynamics, cumulus-oocyte communication, and epigenetic regulation are shaping the design of tailored culture environments. Despite promising progress, significant challenges remain in replicating the complexity of in vivo folliculogenesis, particularly in non-rodent models. Addressing these challenges will be critical to expanding the oocyte pool available for reproductive and biotechnological applications, with broad implications for fertility preservation, livestock breeding, and fundamental research.