CHRONOLOGICAL CHANGES IN THE MEIOTIC PROG RESS OF IN-VITRO MATURATIONOF BOVINE OOCYTES

In this study, the chronological changes in the meiotic progress of in vitro maturation of bovine oocytes was analysed. Oocytes (n = 1044) w ere obtained from a local abbatoir and were classified into two groups according to the presence or absence of cumulus cells. They were incu bated in microdrops (5 per drop) in TCM-199 (control),TTCM-199 + 10% f etal calf serum (treatment 2) and TCM-199 + 10% estrous cow serum (tre atment 3). Oocytes were fixed and stained at the end of 0, 6, 12, 18, 24 and 30 h of the beginning of in vitro culture, were evaluated accor ding to the nuclear stage of maturation. These results demonstrated th at the immature oocytes at the time of collection (0 h) were in the ge rminal vesicle stage (GV), and that the highest maturation rate was at 24 h of culture in all treatments. Serum treatments enhanced the matu ration rates obtained (52.1 and 55.7%) compared to control (serum-free ) medium (42.7%; P < 0.05) in cumulus-cell-enclosed oocytes. In denude d oocytes, the maturation rates were lower compared to cumulus-cells-e nclosed oocytes in all treatments. In conclusion, meiotic progression of bovine oocytes can be influenced by the inclusion of sera in the ma turation media and by the presence of the cumulus cells.