Successful fertilization in vitro of fresh intact oocytes by perivitelline (acrosome-reacted) spermatozoa of the rabbit.

The ability of supplementary rabbit spermatozoa recovered from the perivitelline space of fertilized eggs to penetrate and fertilize fresh oocytes was determined. One-cell cell embryos were recovered from superovulated does approximately 4 hours after ovulation. The perivitelline spermatozoa were released by rupturing the zona pellucida of mechanically and enzymatically denuded 1-cell embryos and then fresh cumulus-intact oocytes were added. Fertilization of fresh oocytes was evaluated by pronuclei and second polar body formation. Thirty-three of 143 oocytes (24%) were fertilized by perivitelline spermatozoa. Of these, eight (24%) progressed to normal 2-cell embryos in vitro. These data suggest that some completely acrosome-reacted perivitelline rabbit spermatozoa retain the ability to penetrate the cumulus, bind and penetrate the zona pellucida, and fuse with the vitellus of fresh intact unfertilized oocytes to initiate apparently normal embryonic development.