The effect of temporary meiotic attenuation on the in vitro maturation outcome of bovine oocytes.

The aim of this study was to investigate the effect of delaying maturation by extended culture of immature bovine oocytes in prematuration medium (PMC) containing single maturation inhibitor on their meiotic resumption and embryonic development. Bovine immature oocytes were cultured in M199 containing 10 μM of either inhibitor (roscovitine, cilostamide, or forskolin) for either 72 or 120 h followed by up to 48 h in maturation media supplemented with 7.5 IU follicle-stimulating hormone (FSH)/luteinizing hormone (LH). Two control groups were used. In untreated control, immature oocytes were cultured in the same medium as the experimental group without any inhibitors. In the FSH/LH control group, oocytes were cultured directly in the maturation medium supplemented with FSH/LH up to 48 h. In vitro matured oocytes were then inseminated with frozen-thawed bull sperm. Fertilization, defined as two-cell division 48 h post-insemination, and blastocyst formation were recorded. Total maturation rate for the 72-h group was 73%, 70%, 66%, and 69% for roscovitine, forskolin, cilostamide, and FSH/LH control, respectively, with no significant difference indicating that inhibitors have no negative effect on the oocyte maturation rate. The total fertilization rate for the 72-h group revealed that cilostamide (47%) and roscovitine (35%) were significantly higher than FSH/LH control (20%). The total blastocyst formation rates per inseminated oocytes revealed that among treatment groups, roscovitine (20%) had significantly higher rate than forskolin (9%). Overall, 72-h exposure period had better outcomes than 120 h in all the treated groups. In conclusion, prematuration culture of the bovine oocytes in the presence of maturation inhibitor for 72-h period at 10 μM concentration is sufficient in improving the bovine oocyte developmental competence.