In an attempt to enhance embryo development, we have co-cultured 1-cell OF1 mouse embryos on bovine kidney epithelia (Madine-Darby bovine kidney; MDBK) cells in a complex medium called complex mouse tubal fluid (cMTF; based on the energy substrate levels found in the mouse oviduct, containing non-essential amino acids, glutamine and EDTA). To determine the quality of the blastocysts obtained, we examined several parameters: morphology, total cell numbers, inner cell mass (ICM):trophectoderm (TE) ratio, glycolytic activity and viability after transfer. A significantly lower number of blastocysts developed on MDBK cells compared with cMTF medium. cMTF blastocysts had a significantly higher glycolytic activity and a lower blastocyst cell number than those grown in co-culture, while both in-vitro groups had higher ICM:TE ratios compared with in vivo. Blastocysts grown on MDBK cells displayed an elevated ICM number compared with those grown in cMTF medium alone. However, the percentage of fetuses after transfer remained drastically low in both culture groups compared with in-vivo blastocysts. In conclusion, co-culture did not increase the number of zygotes reaching the blastocyst stage. Although co-culture blastocysts show some similarities to in-vivo embryos in cell number and glycolytic activity, no enhancement in viability was observed.