Two-step freezing of cattle blastocysts with dimethylsulfoxyde (DMSO) or glycerol

Sixty five cattle blastocysts were frozen by the so-called two-step freezing method: The samples were seeded at -7 degrees C and then directly brought at -30 degrees C for 30 minutes before being taken into liquid nitrogen. Results in terms of survival rates at thawing and after short term cultures were compared to two controlled linear cooling rate procedures (i.e. 0.3 degrees C/min and 1.3 degrees C/min). The results demonstrate that: 1) two-step freezing yielded approximately the same survival rate as the two others techniques and 2) Glycerol yielded better survival rates than DMSO treatments (56 vs 31% after 24 hours in culture).