SURVIVAL OF IVF-DERIVED BOVINE EMBRYOS FROZEN IN GLYCEROL OR ETHYLENE-GLYCOL

Survival of IVF-derived bovine embryos of different ages and stages of development, produced in 2 different co-culture systems and frozen in 2 different cryoprotectants, was investigated. In vitro-derived bovin e embryos (n=5,525) were utilized to study survival following exposure to cryoprotectants and after freezing. Survival of the frozen embryos was based on blastocyst re-expansion 24 h and hatching 72 h after tha wing. There was no difference in survival when embryos were exposed to either glycerol (Gly) or ethylene glycol (EG) for 10 or 40 min with t he cryoprotectant diluted with or without freezing. In 2 of 3 experime nts in which a comparison was possible, more blastocysts frozen in 1.4 M glycerol than in 1.5 M ethylene glycol survived. Addition of 0.25 M sucrose to 1.5 M ethylene glycol in the freezing solution did not imp rove embryo survival. More blastocysts frozen on Day 7 of in vitro cul ture survived than those frozen on Day 6 or Day 8. On Days 6, 7 and 8, embryos in the most advanced stage of development survived better tha n those at less advanced stages. Post-thaw survival did not differ for embryos produced in co-culture with Buffalo Rat Liver (BRL) cells wit h either Menezo B2 Medium or Tissue Culture Medium 199 and frozen in 1 .4 M glycerol. (C) 1997 by Elsevier Science Inc.