THE EFFECT OF PUNCTURING THE ZONA PELLUCIDA ON FREEZE-THAW SURVIVAL OF BOVINE EMBRYOS

The zona pellucida of fertilized bovine embryos of the morula stage (day 6) were punctured using a micromanipulator and a glass knife. In the presence of 2 M DMSO, 23 embryos were cooled (0.5 °C/min) to −196 °C and, upon thawing (10 °C/min), transferred into nine recipients. Although the embryos, before and after the freeze-thaw cycle, were morphologically indistinguishable, only one calf was born. The role of the zona pellucida during freezing and thawing is discussed.