Effects of cooling rates and maturity of the animal on the recovery and fertilization of frozen-thawed rodent eggs

Abstract

Mouse, rat, golden hamster and Mongolian gerbil eggs were cooled to -75°C in efforts to determine an optimum cooling rate for freezing unfertilized rodent eggs. The best cooling rate for the recovery and in vitro fertilization of mouse and rat eggs was 0.33°C/min from -4° to -45°C followed by 1°C/min from -45° to -75°C. Hamster eggs could withstand a wider variation in the rate of cooling since large numbers of eggs could be recovered at 0.33°, 0.5° or 1°C/min; and fertilized in vitro. In contrast with the other species gerbil eggs froze poorly at these same rates of cooling. Eggs from mature mice and rats consistently withstood freezing better than those from immature females (P<0.001) when cooled at 0.33°C/min.