Influence of stage of maturation of bovine oocytes at time of vitrification on the incidence of diploid metaphase II at completion of maturation

The present study was to verify the incidence of bovine diploid oocytes whe n vitrified at various maturation stages. Bovine cumulus-oocyte complexes w ere recovered from ovaries at a slaughterhouse and then divided into five g roups: control group (unvitrified oocytes), 0 h group (composed of oocytes vitrified before the onset of maturation) and 8, 12, and 22 h groups (vitri fied respectively at 8, 12 and 22 h after the onset of maturation). The ooc ytes remained vitrified for 24 h, and then were thawed. In all groups, the oocytes completed 24 h of maturation. Subsequently, the cumulus cells were removed, and the denuded oocytes fixed on slides and stained with aceto-orc ein. No differences (P > 0.05) in the incidence of diploid metaphase IT ooc ytes were observed between the control, nonvitrified group (2.4%, 1/41) and oocytes vitrified at 12 h (6.9%, 3/43) or 22 h (2%, 1/50). However, signif icantly (P < 0.05) more diploid oocytes were detected after vitrification a t 0 h (28.5%, 10/35) or 8 h (35.4%, 11/31) of maturation. These results sug gest that the nuclear stage at which bovine oocytes are vitrified may affec t the incidence of diploid oocytes, especially in oocytes vitrified before maturation or 8 h after the onset of maturation. (C) 2001 Elsevier Science B.V. All rights reserved.