Intra-ovarian regulation of follicular development and oocyte competence in farm animals.

In both mono-ovulatory species, such as cattle, and poly-ovulatory species, such as pigs, the interactions among extra-ovarian gonadotropins, metabolic hormones and intra-ovarian growth factors determine the continued development of follicles, the number of follicles that ovulate and the developmental competence of the ovulated oocyte. FSH and then subsequently LH are the main hormones regulating antral follicle growth in both mono- and poly-ovular species. However, a range of intra-ovarian growth factors, such as insulin-like growth factors (IGFs) and bone morphogenetic proteins (BMPs), are expressed throughout follicle and oocyte development and interact with gonadotropins to control follicle maturation. In addition, environmental factors such as nutrition, including both the amount and composition of the diet consumed prior to ovulation, can influence follicle development and the quality of the oocyte. Recent progress in our understanding has resulted in the development of diets that enhance oocyte quality and improve pregnancy rate in both pigs and cattle. In conclusion, despite some species-specific differences, similar interacting mechanisms control follicular development and influence oocyte quality.