Abstract: To explore the suitable activation methods for in vitro parthenogenetic development of matured bovine oocytes and increase the efficiency of nuclear transfer for embryonic parthenogenesis, we have studied the effects of activation by ethanol (EH), ionomycin (Ion), A23187, 6-dimethyl-aminopurine (6\|DMAP: 2 mmol·L-1) or cytochalasin B (CCB) on the development of bovine oocytes. Meanwhile, we have analyzed the effects of different numbers of cumulus cell layers on parthenogenetic development of bovine oocytes in the same condition. The results showed that (1) Ion(5 μmol·L-1), A23187(10 μmol·L-1) or ethanol(7%) applied together with 6-DMAP(2 mmol·L-1) and cytochalasin B (CCB) significantly activated the growth of bovine parthenogenetic embryo, with treatment of Ion＋6-DMAP＋CCB showing the strongest effects as compared to other groups(P<0. 01). Thus, CCB is beneficial to the development of bovine parthenogenetic embryos.(2) The number of cumulus cell layers coating oocytes had significant effects on parthenogenesis development after parthenogenetic activation. The rate of cleavage and blastocysts for bovine cumulus oocyte complexes (COCs) containing 3-5 or above 6 cumulus cell layers were 69.09%, 31.58% and 75.14%, 38.85%, respectively. These two groups had no significant difference(P>0. 05), but were significantly higher than the group containing 1-2 lays and the mixed group(P<0.05). Therefore, cells of these two groups were the optimal research material for experiment of parthenogenetic activation of in vitro embryo development in bovine．

Key words: bovine, oocytes, in vitro maturation, parthenogenetic activation, chemical activator