SUCCESSFUL VITRIFICATION OF EARLY-STAGE BOVINE IN-VITRO PRODUCED EMBRYOS WITH THE OPEN PULLED STRAW (OPS) METHOD

A new method was introduced to cryopreserve early stage bovine embryos . 250 mu l straws were heat-softened and pulled to halve the diameter. After a 2-step equilibration in ethylene glycol, dimethylsulphoxide a nd sucrose in TCM-199, the embryos were loaded into the end of the str aws using the capillary effect. The straws were submerged immediately into liquid nitrogen without sealing. At warming, the open end of the straw was immersed directly medium with sucrose at 39 degrees C follow ed by 2-step rehydration and in vitro embryo culture. For embryos vitr ified on Day 2, 3 and 4 after insemination, the blastocyst rates on Da y 8 were 27, 43 and 52%, respectively. Control embryos vitrified in th e original straws did not survive the procedure. Results achieved by t he method are most likely attributed to the high cooling and warming s peed, immediate dilution and less severe fracture damage.