Abstract Background The timing of the first postpartum ovulation is an important factor affecting the timing of estrous resumption in dairy cows. The first postpartum ovulation is delayed in cows producing large amounts of milk with an intensive negative energy balance. The antral follicle count (AFC) and serum anti-Müllerian hormone concentrations are known to be indicators of the ovarian reserve, which is the number and quality of follicles left in a pair of ovaries and known as an indicator of female fertility. Cows with higher AFC have been proven to show higher pregnancy rate and shorter calving to conception intervals; however, the relationship between the timing of the first postpartum ovulation and ovarian reserve remains unclear. Therefore, this study examined the relationships between postpartum follicular dynamics, the ovarian cycle, nutritional status, and ovarian reserve. Methods Transrectal ultrasonography was conducted from calving to 70–120 days in milk (DIM) in 26 cows to monitor AFC, follicular dynamics and the ovarian cycle. Body weight (BW) and milk yield were used as indicators of nutritional status. Results The first postpartum ovulation was significantly later in cows with low AFC (
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