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Multiple preovulatory follicles developing upon superovulation (SO) are heterogeneous in quality, which may be the consequence of follicular development deviating from that in untreated cyclic cows. Therefore, we investigated follicle performance in terms of estradiol (E), progesterone (P), and testosterone (T) concentrations in the fluid of stimulated preovulatory follicles (FF), in particular at onset of final maturation as initiated by the LH surge. Pre-synchronized HF cows (n = 25) were treated with oFSH (Ovagen; ICP, Auckland, New Zealand) for SO, and FF were collected 2 h pre-LH surge (n = 9 cows), and 6 h (n = 8) and 22 h C(n = 8) post-LH. At Day 9 (estrus = Day 0), a norgestomet ear implant (Crestar; Intervet International BV, Boxmeer, The Netherlands) was inserted, and SO treatment was started at Day 10 using oFSH i.m. twice daily in decreasing doses during 4 days (total dose 17 mL). Prostaglandin (22.5 mg PG; Prosolvin, Intervet) was administered i.m. concomitant with the 5th dose of FSH. Ear implants were removed 50 h after PG and then GnRH (0.021 mg Receptal; Intervet) was administered i.m. inducing the LH surge 2 h later. Ovaries were collected by laparotomy at the time of GnRH, and 8 and 24 h later and all follicles sized >10 and 8 mm from 23 cows at 30 h after PG, that is, preceding the LH surge, following treatment with 3000 IU eCG i.m. (Folligon; Intervet) on Day 10 and 15 mg PG on Day 12; (2) 12 FF of the dominant follicle from 12 untreated cyclic cows after ovariectomy 48 to 62 h after onset of luteolysis, that is, shortly before the natural LH surge. The concentrations (ng/mL FF) of E, P, and T were estimated by our validated RIAs. Data (mean ± SEM) were analyzed by ANOVA. The levels of E, P and T of the oFSH group were pre-LH: 399 ± 35, 49 ± 6 and 13 ± 2; 6 h post-LH: 194 ± 11, 202 ± 12, and 14 ± 1; and 22 h post-LH: 35 ± 2, 200 ± 23, and 7 ± 1, respectively. Although the change in E and P levels between the different time points after LH is in agreement with that reported for untreated cyclic cows (Dieleman et al. 1983 J.Endocrinol. 97, 31–42), the concentrations were lower. However, the most striking finding was the significantly lower E in pre-LH FF after oFSH compared to that after eCG (1302 ± 82) or of cyclic cows (1942 ± 200). The P levels in FF of the respective pre-LH groups were not significantly different. The much lower E level after oFSH is possibly due to the low or even absent LH bioactivity for oFSH in comparison to eCG. It could also indicate a lower developmental potential of oocytes following oFSH. However, it is known that SO with oFSH results in regular yields of transferable embryos similar to that after eCG. In view of the high variability of the E level in FF, it is concluded that selection of follicles for high E levels is a prerequisite when investigating oocyte development and maturation.

323 THE QUALITY OF PREOVULATORY FOLLICLES DURING FINAL MATURATION IN COWS STIMULATED WITH oFSH AND A DEFINED LH SURGE