Follicular Development in Gilts Selected for High Ovulation Rate and Embryo Survival Versus Randomly Selected Control Line Gilts

1998 University of Nebraska-Lincoln Extension Swine Report. The patterns of follicular development during the proestrous period were compared in gilts selected for an index of high ovulation rate and high prenatal survival (White Line-2, WL-2) and randomly selected controls (White Line-1, WL-1) on days 0, 2, 3, 4, 5 and estrus after induced luteolysis with PGF2a on day 13 (day 0) of the estrous cycle. Numbers of follicles (F) equal or greater than 2 mm in diameter were categorized and recorded as follows: small (SF, 2 to 2.9 mm), medium-1 (M1F, 3 to 4.9 mm), medium-2 (M2F, 5 to 6.9 mm) and large (LF, equal or above 7 mm). The population of SF was greater in WL-1, whereas the population of M1F was greater in WL-2 gilts during the early follicular phase. The SF and M1F populations declined rapidly in both lines between days 0 and 4. White Line-2 gilts maintained a larger pool of M2F between days 0 and 4. Medium-2 follicles declined in both lines between days 4 and 5, but the loss of M2F was much greater in WL-2 gilts. Large follicles developed earlier and accounted for a greater percentage of the follicles in WL-1 gilts to day 4. The reverse was true on day 5 and at estrus. White Line-2 gilts tended to have greater numbers of large follicles than WL-1 gilts at estrus. White Line-2 gilts maintain a larger pool of M2F during most of the follicular phase and must select a greater number of these follicles during the late follicular phase to achieve their ovulation rate advantage. It is possible the M2F population is healthier in WL-2 gilts.