Abstract: The objective of this article was to investigate the effect of 4 different chemical activation reagents on the rate of development of bovine reconstructed embryos produced by intracytoplasmic direct injection. The reconstucted embryos were randomly divided into 4 groups to be activated:
Ionomycin+6DMAP; Ionomycin+Cycloheximide (CHX);7% ethanol+6DMAP;7% ethanol+CHX. The reconstructed embryos were activated for 5 min in Ionomycin and 7% ethanol. 6DMAP，4 h; CHX， 5 h. The reconstructed embryos were cocultured with cumulus cell monolayer. The rate of cleavage of the 4 groups were 52.6%，52.8%，53.8% and 54.2%， respectively. There was no significant difference among the 4 groups in terms of the rate of cleavage. The rate of blastocyst at day 8 were 20.0%，8.5%，10.2% and 6.1% for groupⅠ，Ⅱ，Ⅲ and Ⅳ， respectively. The rate of blastocyst of group Ⅰ was significantly higher than that of three other groups. The rate of hatching blastocyst of group Ⅰ showed very significant difference with that of group Ⅱ，Ⅲ and Ⅳ (10.7%，2.3%，3.0% and 1.8%， respectively， P<0.01). The results showed that all of the 4 kinds of activation reagents could successfully activated the reconstructed bovine embryos. The group Ⅰ gained the highest rate of blastocyst and hatching blastocyst， which demonstrated that Ionomycin+6DMAP benefited the development of bovine reconstructed embryos and could obtain an ideal rate of blastocyst. Ionomycin+6DMAP were ideal activation reagents for bovine reconstructed embryos produced by intracytoplasmic direct injection.

Key words: bovine; oocyte; intracytoplasmic direct injection; reconstructed embryo; chemical activation