ELSEVIER OVERALL EFFICIENCY OF IN VITRO EMBRYO PRODUCTION AND VITRIFICATION IN CATTLE G. Vajta. P. Helm. T. Greve and H. Callesen Embryo Technology Center, Danish Institute of Animal Science DK-8830 Tjele, Denmark Department of Clinical Studies, Reproduction, Royal Veterinary and Agricultural University DK-1870 Frederiksberg C, Denmark Received for publication: ApriZ 25, 1995 Accepted: JuZy 11, 1995 ABSTRACT In 5 replicates a total of 719 immature oocytes recovered from 94 slaughterhouse-derived bovine ovaries were matured and fertilized in vitro, then cultured for 7 to 9 d on a granulosa cell monolayer in TCM 199 supplemented with calf serum. Of 338 blastocysts (47% of oocytes cultured), 301 were vitrified in Hepes/bicarbonate buII+ed TCM-199 medium 20% calf serum and dimethylsulfoxide and ethylene glycol as the cryoprotectants. After thawing in 1 M sucrose and subsequent culture in vitro, 237 (79%) of the blastocysts re-expanded and 177 (59%) hatched. Re- expansion and hatching rates differed between the blastocysts vitrified on Day 7 and Day 8 (84 and 69% vs 70 and 41%, respectively). We conclude that the applied methods are relatively simple and inexpensive to use, with an overall efficiency of the in vitro production/vitrification procedure being 1.9 hatched blastocyst/ovary. Therefore, this system seems suitable for large-scale production of cryopresetved bovine embryos for various purposes. Key words: bovine, embryo, in-vitro production. vitrification INTRODUCTION In most experiments concerning in vitro production of cattle embryos. the oocytes originate from pools of ovaries collected at slaughter. However, a wider commercial application of in vitro techniques will require the production of embryos from individual animals making the number of transferable embryos per ovary produced in vitro an important characteristic of the method. To date information has been described for fresh embryos originating from individually collected or pooled ovaries (3,4,6, 7, 19.24). Recent reports have indicated that vitrification of in vitro produced embryos is at least as efficient as conventional freezing (15. 16. 18.23). However, selected embryos were used in earlier Acknowledgments The authors wish to thank 2s. BQr&rdi, I. Kiss and Z. Mach&y for their valuable help in establishing the initial in vitro production and vitrification method in Hungary. Theriogenology 45:683-689, 1996 0 1996 by Elsevier Science Inc. 655 Avenue of the Americas, New York, NY 10010 0093-691 X/96/$1 5.00 SSDI 0093-691X(95)00414-9