Information in this paper is intended to complement current AI programs and to assist individuals that intend to initiate AI programs. Furthermore, the success of AI depends not only on appropriate semen collection and handling and insemination techniques, but also on a thorough comprehension of normal and abnormal reproductive events in the female pig. The pig typically has an estrous cycle of approximately 21 days duration, but the cycle commonly varies from 17 to 25 days.
Mature follicles have taut, almost transparent walls and contain straw-colored fluid.
The LH surge is necessary to induce ovulation or rupture of the follicles with the subsequent release of ova. Onset of estrus usually coincides with the preovulatory LH surge and depending upon age, females may be sexually receptive for 1 to 3 days. Consequently, most producers breed or inseminate at various intervals after the onset of estrus to ensure fertilization. Following ovulation, collapsed follicles are 4-5 mm in diameter. The CL produce the steroid hormone, progesterone.