Modification of follicular dynamics by exogenous FSH and progesterone, and the induction of ovulation using hCG in postpartum beef cows

摘要

In the first of 2 experiments, cows were injected on day 21 postpartum with 10 ml saline (control; n = 6), 200 mg FSH (Folltropin-V; n = 6) or received a progesterone-releasing intravaginal device (PRID, 1.4 g progesterone; n = 5) for 10 days. FSH and PRID prolonged (P<0.01) maintenance of a dominant follicle (15.5±1.16 and 14.4±1.29 days respectively vs. 8.4±1.22 in control), and increased (P<0.05) the maximum diameter of the dominant follicle (14.0±0.91 and 16.4±1.01 vs. 10.9±0.95 mm). The PRID-maintained dominant follicle ovulated in 60% of cows, followed by normal oestrous cycles (vs. 0% in control; P = 0.01), whereas the dominant follicle ovulated in 33% of FSH-treated cows (P = 0.08). PRID shortened the interval to first ovulation precedinga normal cycle and continued cyclicity (44±4.1 vs. 60±4.4 days in control; P = 0.02). In experiment 2, cows (16 per treatment) received saline (control), saline + PRID or FSH + PRID. 60 h after PRID withdrawal, cows (8 per treatment) received saline or 1500 IU HCG (Progon 10 000). FSH + PRID increased the number of large (>10 mm in diameter) follicles (3.6±0.43 vs. 1.9±0.39 in control; P = 0.005). Compared with the control, PRID and FSH + PRID respectively prolonged (P<0.05) maintenance of the largest follicle (11.0±0.82 and 11.2±0.91 vs. 8.7±0.81 days). PRID-maintained dominant follicle ovulated in 50% of cows, followed by normal oestrous cycles. FSH + PRID-maintained largest follicle was atretic at PRID withdrawal and was anovulatory. Compared with PRID, FSH + PRID + HCG increased (P = 0.03) the incidence of ovulation preceding a cycle of normal duration and continued cyclicity (100 vs. 50%), and reduced (P = 0.04) the interval to first ovulation preceding a cycle of normal duration and continued cyclicity compared with the control (38±6.5 vs. 58±6.3 days). The area under the progesterone curve during the induced cycle was reduced (P = 0.002) after (PRID±FSH) + HCG than after PRID±FSH. It is concluded that PRID alone or with FSH/HCG has the potential to modify the dominant follicle and initiate cyclicity in postpartum beef cows.