Effect of follicular aspiration at the onset of progesterone-based timed artificial insemination on the follicular dynamics and fertility of early postpartum Japanese black cows

The effect of gonadotropin-releasing hormone analogue (GnRH-A) or follicular aspiration at the onset of progesterone-based timed artificial insemination (TAI) on subsequent follicular growth and synchronization of ovulation was examined in early postpartum Japanese Black cows. A total of 40 (22 in Exp. 1 and 18 in Exp. 2) Japanese Black cows at 20-30 days postpartum were fitted with a progesterone releasing internal device (PRID) for 7 days, injected with a prostaglandin F2α analogue upon removal of the PRID and GnRH-A 48 h later, and inseminated 18 h after GnRH-A injection. In Exp. 1, the animals were divided into three groups (untreated control, GnRH-A injection or follicular aspiration) of different treatments on the first day of PRID insertion (day 0), and the synchronized ovulation rate in the follicular aspiration group (100%; 8/8) tended to be higher (P = 0.077) than that in the control group (42.9%; 3/7). In Exp. 2, follicular growth in the GnRH (n = 9) and follicular aspiration (n = 9) groups was monitored by ultrasonography. Four out of the nine animals in the GnRH group had a corpus luteum on either day 4 or day 7 (OV group), and the other five animals had no induced ovulation (NOV group). The diameter of the ovulatory follicle on day 9 in the OV group (1.44 ± 0.11 cm) tended to be greater (P = 0.078) than that in the NOV group (1.13 ± 0.07 cm). Follicular aspiration at the onset of PRID-based TAI of early postpartum Japanese Black cows, regardless of the resumption of ovarian cyclicity, tended to result in a higher rate of synchronization of ovulation than that of the untreated controls.