Female pigs are not sexually receptive during these periods of progesterone production. This event is evident by the change in color of the CL from reddish-pink to yellow and a gradual decrease in diameter. Follicular recruitment begins on Days 13-15 and follicular enlargement and hyperemia are obvious by Day 17. The CA gradually regress during lactation and are less than 2 mm in diameter at the time of weaning. Follicular development is minimal and few follicles are greater than 4 mm during lactation.
Follicles continue to increase in size as the animal approaches estrus following weaning.
Cervical relaxation and increased secretion of mucus in the cervix, anterior vagina and uterus are observed in the proestrual reproductive tract. In contrast, estradiol from the maturing follicles produces dramatic changes in the reproductive tract during estrus. Most of the multiple large cysts have some luteinized tissue and produce sufficient progesterone to inhibit estrous cyclicity. Sows with these cysts usually fail to exhibit estrus and are culled from the herd. Since these animals fail to ovulate, it is unlikely that these animals conceive.