The present study aimed to establish an efficient system for the production of female embryos from dairy cows by in vitro fertilization (IVF) using X-sorted sperm and in vivo-matured oocytes collected by ovum pick up (OPU). Nonlactating Holstein cows (n=36) were administered a controlled intravaginal progesterone-releasing (controlled internal drug release) device (d 0), underwent dominant follicle ablation (DFA) or ovulation by administration of 100μg of GnRH on d 5, and were superstimulated with FSH and PGF2α, following standard procedures. Controlled internal drug release devices were removed on the evening of d 8 or on the morning of d 9, depending on the experiment. For LH surge induction, 200μg of GnRH was administered on the morning of d 10 (0h). In experiment 1, the peak (48.1%) of ovulating follicles was detected at 29 to 32h after GnRH injection (0h), and the range in the timing of the initiation of ovulation was less by timing from GnRH administration (30.0±2.8h) rather than by timing the onset of estrus (32.7±4.7h). Only 0.9% of total ovulated follicles were recorded before 26h after GnRH injection. Therefore, OPU was carried out at 26h and IVF occurred at 30h after GnRH in experiments 2 and 3. In experiment 2, 83.3±10.8% of oocytes with expanded cumulus cells had extruded the first polar body at 30h after GnRH injection. The aim of experiment 3 was to compare the effect of either DFA or GnRH-induced LH surge before superstimulation on the efficiency of embryo production by IVF following superstimulation. Progesterone concentrations from d 10 to 12 in the DFA group were lower than those in the GnRH group. A greater proportion of recovered oocytes with expanded cumulus cells from ≥8-mm follicles was observed in the DFA group than in the GnRH group (95.9 and 77.4%, respectively). Blastocyst rates in the DFA and GnRH groups (58.0 and 52.8%, respectively) did not differ from those of oocytes collected from nonstimulated OPU and matured in vitro (49.9%). However, the proportion of high-quality blastocysts was higher in the DFA group compared with the GnRH group (54.9 vs. 21.5%). Our results demonstrate that high rates of good-quality blastocysts can be produced by IVF with X-sorted frozen sperm using in vivo-matured oocytes collected by OPU from cows after DFA and superstimulation combined with ovulation induction.
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