Effect of post-thaw cell rehydration at 4 degrees C on survival of frozen and vitrified IVP-derived bovine embryos

In vitro-produced bovine embryos (IVP) were either frozen in 10 % glycerol in a phosphate-buffered saline solution (PBS) using conventional slow freez ing or vitrified in 25 % glycerol and 25 % ethylene glycol in PBS. The resu lts of viability and hatching rates were compared between frozen and vitrif ied embryos after thawing and dilution using one of three different protoco ls: (A) a three-step dilution procedure, (B) a one-step dilution procedure or (C) a procedure in which embryos were kept in situ inside the straw at 4 degrees C for 10 min during a one-step dilution procedure. No significant differences in embryo survival were found among protocols A, B and C for fr ozen embryos and between protocols A and B for vitrified embryos. Viability and hatching rates of vitrified embryos thawed and diluted by protocol C ( 73 and 62 %) were significantly enhanced (P < 0.05) in comparison to those obtained with protocol A (55 and 41.6 %) or protocol B (54.5 and 35.3 %). T hese results indicate that for vitrified IVP bovine embryos, direct in-stra w rehydration at 4 OC for 10 min improves embryo survival and it could be a practical procedure for use under field conditions where there is sometime s a longer interval between thawing and transfer. (C) Inra/Elsevier, Paris.