POLYVINYL-ALCOHOL AS A DEFINED SUBSTITUTE FOR SERUM IN VITRIFICATION AND WARMING SOLUTIONS TO CRYOPRESERVE OVINE EMBRYOS AT DIFFERENT STAGES OF DEVELOPMENT

The purpose of this study was to assess the viability of ovine embryos after replacing fetal calf serum (FCS) with polyvinyl alcohol (PVA) i n vitrification and warming solutions. Ovine embryos were obtained fro m superovulated Sardinian breed ewes at 4, 5, 6, and 7 days after inse mination. All vitrification and warming solutions were prepared using buffered saline solution with 20% FCS (group a) or 0.1% PVA (group b). Embryos were vitrified in 20 mu l of glycerol 3.4 M + ethylene glycol 4.6 M and loaded into the centre of 0.25 mi straws between two column s of sucrose solution (0.5 M), and plunged immediately into liquid nit rogen. After being warmed in a water bath at 35 degrees C for 10 s, th e vitrified embryos were moved to 0.25 M sucrose solution for 3 min. E mbryos were cultured in TCM-199 after washing with 10% FCS and sheep o viductal epithelial cells up to hatching or re-expansion of the blasto coelic cavity. No significant difference in the viability rates was ob served between embryos vitrified/warmed in PVA or FCS solutions. In bo th groups, the rate of in vitro viability was (P < 0.01) lower at the precompacted and compacted morula stages than at the expanded, hatchin g or hatched blastocyst stage. In both groups, early blastocysts were less viable than expanded (P<0.01), hatching or hatched blastocyst (P < 0.05). There was no significant difference in survival rates at days 14 (79 and 76%) and 45 (63 and 59%) after transfer into synchronised recipients between vitrified expanded blastocysts of groups a and b, r espectively. These results suggest that it is possible replace serum w ith PVA in vitrification and warming solutions without reducing in viv o and in vitro viability. (C) 1997 Elsevier Science B.V.