Ovarian follicular development following administration of progesterone or aspiration of ovarian follicles in Holstein cows

The objective of this study was to compare the effects of administration of a single injection of progesterone (P-4) and follicle aspiration on Day 7 of the estrous cycle on the timing and synchrony of follicular wave emergence, time of ovulation, and concentrations of P-4 estradiol and FSH in Holstein cows. Twenty cows were assigned to 4 groups (n=5 cows per group) in a 2 by 2 factorial arrangement. Cows were treated on Day 7 (Day 0 = estrus) of the estrous cycle with either sham follicular aspiration and an oil vehicle administered intramuscularly (control), aspiration of ovarian follicles (aspiration), 200 mg of P-4 im, or aspiration and 200 mg of P-4 im (aspiration + P-4). On Day 11, PGF(2 alpha)(25mg) was administered to all groups. Synchrony of ovulation vias less variable in each of the treatment groups compared with the control group (P<0.05). whereas ovulation was delayed in cows in the P-4 group (P<0.05). Day of follicular wave emergence was delayed in the cows of the P-4 group compared with cows in the aspiration and aspiration + P-4 groups (P<0.01), whereas variability in wave emergence was less among both groups of aspirated cows compared with the cows in the control group (P<0.01). More follicles 4 to 7 mm in diameter were detected in the 2 aspiration groups compared with the cows in the control and P-4 group (P<0.05). No difference was detected among groups in the maximum concentration of FSH associated with follicular wave emergence. We conclude that both the administration of P-4 and the aspiration of follicles on Day 7 of the estrous cycle improves the synchrony of ovulation, when luteolysis is induced on Day 11 and results in similar concentrations of FSH at the time of follicular wave emergence, but the timing of wave emergence and the number of follicles post-emergence differ. (C) 2001 by Elsevier Science Inc.