Maternal metabolic health and oocyte quality: the role of the intrafollicular environment

Reduced oocyte and embryo quality are currently recognized as key factors in the problem of disappointing fertility in high producing dairy cows, but also in women undergoing assisted reproductive treatment. This review aims to highlight the importance of intrafollicular conditions in the subfertility problem, topical in both bovine and human research. Metabolic disturbances, like a negative energy balance (NEB) early postpartum in the bovine or obesity and type II diabetes in women, are associated with ovarian dysfunction. Changes in the growth pattern of the ovarian follicle, due to suboptimal metabolic conditions, can indirectly affect oocyte quality. Furthermore, maternal metabolic disorders (nutritionally induced, linked with NEB or caused by for example obesity) may alter the endocrine and biochemical composition of the follicular fluid, the microenvironment of the growing and maturing female gamete. The maturing oocyte is very sensitive to any perturbation in its direct environment and in vitro maturation models revealed that some of these metabolic changes have the potential to reduce the oocyte’s developmental competence. Also embryo quality is significantly reduced due to maturation in adverse conditions. Well-balanced and timed oocyte metabolism and gene expression are crucial to safeguard an optimal oocyte development. In that perspective metabolic and transcriptomic parameters of the oocyte may serve to predict reproductive success rates. Importantly, there is also growing evidence that adverse conditions for oocyte growth and maturation may jeopardize the metabolism and health of the offspring.