culture of in vitro produced bovine zygotes in vitro vs in vivo implications for early embryo development and quality the objectives of this study were to examine the effect of culture system on bovine blastocyst formation rates and quality presumptive ivmivf bovine zygotes were cultured either in vitro in synthetic oviduct fluid sof 25 embryos25 microl in 5 co2 5 o2 90 n2 at 39 degrees c or in vivo in the ewe oviduct approximately 100 embryos per oviduct the recovery rate after in vivo culture was 53 8131530 the blastocyst rate on day 7 was significantly higher for the in vitro system 28 3621278 vs 17 37813 p 00001 however after culture in vitro for a further 24 h there was no difference in day 8 yields 36 4571278 vs 32 258813 for in vitro and in vivo culture respectively there was no difference in blastocyst cell number between treatments day 7 96 vs 103 day 8 78 vs 85 for in vitro and in vivo culture respectively irrespective of culture system day 7 blastocysts had a significantly higher cell number than those appearing on day 8 there was no difference in pregnancy rate at day 35 after fresh transfer of a single day 7 blastocyst 375 2156 vs 453 2453 for in vitro and in vivo culture respectively after cryopreservation by freezing in 10 glycerol vs3a vitrification or solid surface vitrification the survival of in vitro cultured embryos was significantly lower than survival of embryos cultured in the ewe oviduct or those produced by superovulation of donors in conclusion these findings demonstrate that while bovine zygotes cultured in vitro are capable of rates of development similar to those of their in vivo cultured counterparts in terms of day 8 blastocyst yield cell number and early pregnancy rate there are significant differences in embryo cryosurvival this suggests that current in vitro culture systems need to be improved to optimize embryo quality and pregnancy rates