THE EFFECT OF SPERM PREPARATION ON THE TIMING OF PENETRATION IN BOVINE IN-VITRO FERTILIZATION

Five hundred and seventy three follicular bovine cumulus oocyte comple xes were matured in vitro and in vitro fertilization (IVF) carried out with the native semen of a brown bull, Half the cultures were fertili zed with transmigrated spermatozoa (TM), the other with sperm suspensi ons prepared using the swim-up (SU) process, Five, six and seven h aft er IVF the oocytes were fixed and stained. Using a phase-contrast micr oscope, both the incidence of penetration and polypenetration and the stage of development of a pronucleus were determined. With the TM samp les, five hours after IVF penetration was observed in 39.3 per cent of the oocytes, whereas with the SU samples the first instances of penet ration were observed only two hours later (4.2%). By this time a norma l-looking pronucleus was observed in 16.4 per cent of the oocytes in t he TM group, Polypenetration was seen only after seven hours of incuba tion. This study showed that TM spermatozoa penetrate the oocyte earli er than SU spermatozoa.