To establish sustainability in the dairy industry, it is important that cows become pregnant at a biologically optimal time and at an economically profitable interval after calving. In this review, the results obtained from Holstein cows in an experimental herd for dairy research are summarized. First, the postpartum follicular dynamics of lactating cows were traced in relation to their fertility. The premature initiation of ovarian activity does not always improve the fertility of cows, as indicated by the number of days open. Second, the occurrence of anestrous ovulations during the early postpartum period was analyzed with reference to the frequency of reversion to anestrus. The premature onset of estrous activity also failed to improve fertility, and relapse into anestrus after the onset of the estrous cycle often occurred during the breeding period. Third, both the emergence and fate of cystic ovarian follicles and repeated follicular waves during the early postpartum period were examined, and it was revealed that neither conditions exerted a significant impact on the cow′s fertility, as indicated by days open. The importance of appropriate estrous detection was underlined and discussed as a major concern to improve the fertility of high-yield dairy cows.