Follicular growth and maturation in the domestic hen (Gallus domesticus).

The rate of follicular development in hens was assessed by measuring the increase in the diameter of follicles during 120 h before ovulation and the mass of follicles during 48 h before ovulation. The rate of follicular maturation was estimated by the ovulatory response of follicles to an injection of GnRH and the ability of follicles to produce progesterone in response to an injection of LH. Follicular diameter and follicular mass increased until ovulation, indicating that the follicle continues to sequester yolk material until ovulation occurs. The ovulatory response to GnRH and the production of progesterone in response to LH were negligible until 10 h after ovulation and then both aspects of follicular competence began to be functional. It was concluded that the size of the hen's ovum is not a primary factor regulating ovulability; rather, the acquisition of the ability to ovulate spontaneously is associated with the ability to produce progesterone in response to an LH stimulus. The ability to ovulate in response to GnRH was acquired more quickly in hens laying long sequences than in hens laying short sequences, indicating that the ovulatory response of the follicle can be used to assess the reproductive potential of laying hens.