A previous report from this laboratory recorded a yield of 60 per cent of embryos recovered at the morulae/blastocyst stage of development after the in vitro maturation and fertilization of bovine follicular oocytes and their subsequent culture in vivo in the sheep oviduct (Lu et al., 1987). When these embryos were transferred by non-surgical procedures to recipient heifers, they established normal pregnancy rates (12/18, 67%) which resulted in the birth of seven sets of twins and five single calves. The objective of the present study was to examine the possibility of large-scale production of cattle embryos using the oocyte maturation and IVF procedures previously employed. A further objective was to determine the effect on embryo yield of transferring varying numbers of fertilized eggs (zygotes) to the sheep oviduct for in vivo culture.

Ovaries were collected fran beef heifers shortly after slaughter and brought to the laboratory within one hour, held at 30°C in phosphate buffered saline supplemented with 0.3 per cent bovine serun albumin and 0.05 mg kanemycin/ml. Non-atretic vesicular follicles (2 - 6 mm diameter) were dissected fran the ovaries and the oocytes liberated by follicule rupture, particular care being taken to preserve the integrity of the oocyte-cumulus-corplex.