Folliculogenesis in the sheep as influenced by breed, season and oestrous cycle

In the sheep the total duration of folliculogenesis, i.e. from the start of development of a primordial follicle to ovulation, is thought to be about 6 months. The initiation of follicular growth as follicles enter the growth phase is influenced by gonadotrophins and, in the sheep, by factors such as breed, season and nutrition. Preantral follicles are characterized by a slow growth rate and no atresia. The number of preantral follicles is influenced by gonadotrophins, age, nutrition, season and unilateral ovariectomy. Antral follicles grow rapidly and produce steroids in response to gonadotrophins.