The time interval between FSH administration and ovarian aspiration influences the development of cattle oocytes

Depriving the ovary of exogenous FSH for 1, 2 or 3 d following a bolus inje ction of FSH was shown to influence the quality of the recovered oocytes. T hus, we compared the developmental competence of oocytes from heifers which had been stimulated for 3 d with FSH (Folltropin(R)-V) and, after an inter val of 36, 48 or 60 h, underwent blind transvaginal aspiration. The ovaries of heifers with a palpable or functional corpus luteum were aspirated to r emove all large follicles 2 d prior to being injected with either 6 doses o f saline (S), 6 doses (20 mg/mL) of FSH (F), or in 6 decreasing doses of FS H (3, 3, 2, 2, 1, 1 mt; Ed). Follicles were counted and classified (medium: 5 to 10 mm, large: >10 mm) with ultrasonography before each aspiration. Th e oocytes recovered were classified, matured, fertilized, and developed in vitro. On a per animal basis, 1.5, 5.2 and 4.7 large and 1.5, 10.7 and 10.7 medium follicles were counted for S, F and Fd, respectively. A mean of 3.3 , 9.1 and 7.7 oocytes was recovered for treatments S, F and Ed, respectivel y and 58, 94 and 82% were enclosed in a nonexpanded cumulus or a corona lay er. Oocyte development rates were based on counts of embryos with 32 or mor e nuclei at Day 6.5. When oocytes were recovered 36 h after the last inject ion, an average of 1, 2.7 and 2 embryos per animal was obtained with S, F a nd Ed, respectively; at 48 h, 0.75, 4.25 and 1 embryo; and at 60 h, 0, 2.5 and 2.7 embryos. Variance analysis was performed, and the protected LSD tes t indicated that treatment F at 48 h resulted in a significantly higher emb ryo rate than Fd at 48 h (P<0.05) or S (all times; P<0.05). The reduced eff ect of the Ed regimen could be due to the decreasing FSH support during fol licular growth or to the lower total amount of FSH given. In conclusion, th ese results indicate an advantage of using moderate (3 d) follicle stimulat ion followed by a period of FSH starvation to obtain optimal embryo product ion. (C) 1999 by Elsevier Science Inc.