FOLLICULAR DEVELOPMENT IN DOMESTIC RUMINANTS

Abstract

Knowledge on the physiological processes that control follicular development may allow for the development of strategies to increase reproductive efficiency in domestic ruminants.  Follicle development depends on the balance between survival factors, proliferation and cell death, which determine whether the follicle starts and continues to grow or is removed from the ovary.  During fetal development of the female, primordial germinal cells (PGC) proliferate by mitosis to reach the gonadal ridge, where the oogonia are surrounded by flattened cells to assemble the primordial follicles.  By the action of kit ligand, BMP-15 and GDF-9, groups of primordial follicles begin their growth until they reach large preantral development where they wait quiescently for new stimuli.  When the animals reach puberty, the cyclic secretion of FSH and LH allow that, subgroups of small antral follicles to resume their growth and ovulate if the endocrine media is adequate.  Follicular development in cows, sheep and goats during the estrous cycle occurs in a pattern like-wave, where groups of follicles begin their growth in response to an increase of FSH, but only some (sheep and goats) or one (cows) is selected as the dominant, and ovulates if its dominance coincides with the lysis of the CL and the reduction of P4.  Among the factors that determine whether a small antral follicle starts, continues and completes its development are its responsiveness to gonadotropins, its steoidogenic capability and the presence of survival and proliferating factors such as IGF-I and VEGF