The vitrification of in vitro fertilized cow blastocysts by the open pulled straw method

In 6 replicates, a total of 450 immature oocytes recovered from 144 slaught erhouse-derived bovine ovaries were matured and fertilized in vitro, then c ultured for 7 to 9 d on a granulosa cell monolayer in tissue culture medium 199 (TCM-199) supplemented with fetal calf serum. Of 126 blastocysts (28% of oocytes cultured), 117 (26% of oocytes cultured) were vitrified in Hepes /bicarbonate-buffered TCM-199 medium and 20% fetal calf serum, with ethylen e glycol and dimethylsulfoxid as the cryoprotectants. After thawing in 1.2 mL holding medium with 0.25-M sucrose and after 1 min in holding medium wit h 0.15-M sucrose, blastocysts were cultivated in vitro for 24 h. The re-exp ansion rate of blastocysts was 69.2% (81 blastocysts), and 39.5% (32 blasto cysts) were hatched. Re-expansion and hatching rates differed between the b lastocysts vitrified on 7 and 8+9 days (74.6% and 46% vs. 62% and 29%, resp ectively). After transfer to recipient cows, 3 out of 6 were diagnosed by u ltrasonography as pregnant. Three calves were born from 18 transfered embry os (16.7%). The open pulled straw (OPS) method seems to be a convenient, simple and eff ective method for cryopreservation of 7 to 9 d bovine embryos. (C) 2000 by Elsevier Science Inc.