Fertilization and development capability of bovine follicular oocytes matured in vitro and in vivo and transferred to the oviducts of rabbits and cows

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Abstract
Follicular oocytes were cultured for 24 h in vitro or obtained 6-24 h after HCG [human chorionic gonadotropin] injection from cows pretreated with PMSG [pregnant mare serum gonadotropin], and transferred to the oviducts of estrous rabbits or heifers, inseminated with bull spermatozoa, to determine their capability for normal development. More than 65% of oocytes cultured in fetal calf serum, equilibrated with 5% CO2 + 5% O2 + 90% N2, matured to metaphase II within 24 h. Fertilization was not obtained in the rabbit oviduct, but about 8% of oocytes matured in vitro underwent parthenogenetic cleavage. Sperm penetration was observed in 49% of oocytes in the cow oviduct, but although 47% had undergone development 96 h after transfer, few developed to morulae and blastocysts, confirming the impaired ability of oocytes matured in vitro, as assessed by nuclear change, to develop normally. Oocytes obtained from heifers slaughtered 24 h after HCG developed normally when transferred to the oviduct of inseminated heifers. Of the oocytes with an activated cumulus, 39% developed to blastocysts; of 16 blastocysts transferred to suitable recipients, 13 developed to normal fetuses at 13-17 wk gestation.