Preovulatory follicle contributions to oocyte competence in cattle: importance of the ever-evolving intrafollicular environment leading up to the luteinizing hormone surge.

ABSTRACT

The preovulatory intrafollicular environment plays a major role in determining oocyte competence. The basis of this review is to highlight the importance of the preovulatory follicle's physiological status prior to the preovulatory luteinizing hormone (LH) surge and onset of oocyte maturation to promote an optimal follicular microenvironment and optimal oocyte developmental competence in cattle. While the underlying mechanisms remain unclear, and are likely multifactorial, the preovulatory follicle's physiological status prior to the preovulatory LH surge is highly influential on the oocyte's capacity to undergo postfertilization embryo development. Changes in the intrafollicular environment of the preovulatory follicle including steroid hormone production, metabolome profiles, and proteome profiles likely support the oocyte's developmental and metabolic competency. This review focuses on the relationship between bovine oocyte developmental competency and antral follicle progression to the preovulatory phase, the role of the preovulatory follicle in improving oocyte developmental competence in cattle, and the importance of the ever-evolving preovulatory intrafollicular environment for optimal fertility.

Bovine pregnancy rates and oocyte developmental competence are heavily influenced by the periovulatory follicular environment. It is well known that the status of the preovulatory follicle at the time of the luteinizing hormone (LH) surge is related to both circulating and intrafollicular hormone concentrations during the follicular phase. Additional relationships between follicle status at the time of the LH surge and oocyte metabolic capacity or modifications in the follicular fluid metabolome and proteome have recently been established. Such studies suggest that critical, multifaceted modifications to the intrafollicular components occur leading up to the LH surge, and that such modifications contribute to the optimal preparation of both the oocyte and intrafollicular environment for oocyte maturation. This review focuses on intrafollicular changes that occur within the dominant follicle from luteolysis to the LH surge and discusses recent advancements in the literature related to how such changes support oocyte competence.