Abstract: Bovine oocytes obtained from OPU (ovum pick up ) were subjected to IVF (in vitro fertilization) and 96 oocytes at MⅡ stage but with IVF failure were selected to stain with Hoechst33342. The data showed that 57 oocytes (59.4%) were not observed the presence of male pronuclei, and the proportion which female and male nuclei did not fuse was 19.8% (19/96), while multi-sperm entrance accounted for 13.5% (13/96). The results suggested that the main reason of bovine IVF failure, on the precondition of oocyte maturation, was caused by the failure of sperm entrance. 

Key words: bovine; IVF; Hoechst33342 stain