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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 PGF2on 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.