Review: Roles of follicle-stimulating hormone in preantral folliculogenesis of domestic animals: what can we learn from model species and where do we go from here?

•The factors regulating ovarian preantral folliculogenesis are still largely unknown.•Evidence from many species point to a role of FSH on the growth of preantral follicles.•FSH activates a complex network of intracellular pathways in ovarian follicles.•Specific pathways stimulated by FSH may depend on follicle stage/local factors.•Detailed understanding of FSH roles will allow the refinement of ovarian stimulation.