Improved in vitro embryo development using in vivo matured oocytes from heifers superovulated with a controlled preovulatory LH surge

In bovine in vitro embryo production, the NM step is rather successful with 80% of the oocytes reaching the MII stage. However, the extent to which th e process limits the yield of viable embryos is still largely unknown. Ther efore, we compared embryonic developmental capacity during IVC of IVF oocyt es which had been matured in vitro with those matured in vivo. In vitro mat uration was carried out for 22 h using oocytes (n=417) obtained from 2- to 8-mm follicles of ovaries collected from a slaughterhouse in M199 with 10% fetal calf serum (FCS), 0.01 IU/mL LH, and 0.01 IU/mL FSH. In vivo matured oocytes (n=219) were aspirated from preovulatory follicles in eCG/PG/anti-e CG-superovulated heifers 22 h after a fixed time GnRH-induced LH surge; end ogenous release of the LH surge was suppressed by a Norgestomet ear implant . This system allowed for the synchronization of the in vitro and in vivo m aturation processes and thus for simultaneous IVF of both groups of oocytes . The in vitro developmental potential of in vivo matured oocytes was twice as high (P<0.01) as that of in vitro matured oocytes, with blastocyst form ation and hatching rates 11 d after IVC of 49.3 +/- 6.1 (SEM; n=10 heifers) vs 26.4 +/- 1.0% (n=2 replicates), and 39.1 +/- 5.1% vs 20.6 +/- 1.4%, res pectively. It is concluded that IVM is a major factor limiting in the in vi tro production of viable embryos, although factors such as the lack of norm al preovulatory development of IVM oocytes contributed to the observed diff erences. (C) 1999 by Elsevier Science Inc.