Optimizing production of in vivo-matured oocytes from superstimulated Holstein cows for in vitro production of embryos using X-sorted sperm

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 100 μg of GnRH on d 5, and were superstimulated with FSH and PGF_2α, 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, 200 μg of GnRH was administered on the morning of d 10 (0 h). In experiment 1, the peak (48.1%) of ovulating follicles was detected at 29 to 32 h after GnRH injection (0 h), and the range in the timing of the initiation of ovulation was less by timing from GnRH administration (30.0 ± 2.8 h) rather than by timing the onset of estrus (32.7 ± 4.7 h). Only 0.9% of total ovulated follicles were recorded before 26 h after GnRH injection. Therefore, OPU was carried out at 26 h and IVF occurred at 30 h 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 30 h 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.