A previous report from this laboratory dealt with the establishment of pregnancies in the early months of gestation after the non-surgical transfer of cattle embryos derived from the in vitro maturation (IVM) of primary bovine oocytes, their fertilization in vitro (IVF) and their subsequent development to the transferable stage (morula/blastocyst) using an in vivo (sheep oviduct) culture system (Lu et al.,1987). The present report deals with some factors affecting the efficiency of IVF and with the culture in vitro of zygotes to the morula/ blastocyst stage of development. Some embryos were frozen and after thawing transferred by non-surgical procedures to five recipient cattle to obtain information on their capacity to undergo further embryonic development.

Primary oocytes, enclosed in cumulus cells, were recovered from vesicular follicles (2-6mm) after their dissection from the ovaries of heifers slaughtered at a local abattoir. The ovaries were brought to the laboratory within one hour of animal slaughter in medium held at 35'C.