In the present study, about 80% of inseminated oocytes were penetrated by sperm, and more than 90% of penetrated oocytes formed both male and female pronuclei. However, 35% of fertilized oocytes were polyspermic. From cleavage rates at 36 h and 48 h after IVF, we estimated that most fertilized oocytes that had formed both male and female pronuclei had cleaved. This was also consistent with the results in Experiment 1 that most uncleaved oocytes at 36-48 h after IVF were unfertilized. These results indicated that fertilized oocytes containing both male and female pronuclei can cleave irrespective of polyspermy or monospermy. Development of polyspermic pig oocytes has recently been demonstrated in our laboratory (unpublished data), although the rate of blastocyst formation and cell number in blastocysts were lower in polyspermic embryos than monospermic embryos. However, it is not clear that the abnormal embryos observed in this study resulted from monospermic oocytes or polyspermic oocytes. ventolin 100 mcg
Because the in vitro-derived embryos used in this study were produced by IVM and IVF, oocyte maturation and activation in vitro may also affect developmental ability of embryos. Incomplete cytoplasmic maturation of pig oocytes matured in vitro was reported previously and included failure of the oocytes to form a male pronucleus after fertilization and inability to develop further. It was found that low male pronuclear formation was due to a low concentration of glutathione in the oocytes, and this has been overcome by supplementation of cysteine, a precursor of glutathione in culture medium.