Low temperature preservation of rabbit embryos.

Rabbit embryos (4-cell, 8-cell and morulae) survived freezing and thawing in the presence of 1-5 M-DMSO. Highest survival rates, assessed by continued development in vitro for 48 to 72 hr, were obtained with cooling rates of 0-74 to 0-90 degrees C/min and thawing rates of approximately 12 and approximately 15 degrees C/min (76%, 83%, 77% and 69% respectively). Transfer of embryos directly to liquid nitrogen after cooling at optimal rates to -110 degrees C instead of -80 degrees C significantly reduced the incidence of rupture of the zona pellucida and mucin coat and increased the rate of recovery. Viability after transfer was low (7% liveborn) and was not correlated with the higher rates of development in vitro to the morula and blastocyst stage.