Transplantation Results of Bovine Embryos Produced by a Two-Step Culture Method.

In this study, the productivity and post-transfer pregnancy rates of bovine embryos in vitro-produced (IVP) by a two-step culture system were compared with those of in vivo-developed (IVD) embryos. Ovum pick-up was designated as Day 0, presumptive zygotes were cultured in modified synthetic oviduct fluid without glucose (mSOFaa), whereas late-stage embryos from Day 5 onward were cultured in TCM 199 supplemented with 5% fetal calf serum and 100 μM β-mercaptoethanol. An average of 5.9 ± 4.8 blastocysts was obtained from 26 donors. A total of 46 fresh and 18 vitrified IVP embryos were transferred individually, resulting in 27 pregnancies (42.2%). Although the pregnancy rate of OPU-IVP embryos was lower than that of IVD embryos (35/60, 58.3%), it was within the range typically reported for commercially available IVP embryos. These findings indicate that the two-step culture method enables efficient production of Japanese Black IVP embryos and is a practical and reliable method for beef cattle production in the field.