BIRTH OF CALVES AFTER DIRECT TRANSFER OF THAWED BOVINE EMBRYOS STORED FROZEN IN ETHYLENE-GLYCOL

The present study investigated the use of ethylene glycol (EG) as a cryoprotectant before the direct transfer of frozen-thawed bovine embryos. Embryos at the morula to blastocyst stages collected on Days 6-8 (estrus designated Day 0) in phosphate buffered saline+20% newborn calf serum were placed into 1.8 M EG or in 1.8 M EG+0.25 M sucrose (EG+SUC), and equilibrated for 13-93 min at room temperature (20-25 degrees C) or 37 degrees C. Each embryo was then loaded into a 0.25 mi straw, and directly placed in the cooling chamber of a freezer precooled at -7 degrees C. After 2 min at -7 degrees C, the samples were seeded, then held for a further 8 min at -7 degrees C, and cooled to -25 or -30 degrees C at -0.3 degrees C min(-1) before being plunged into liquid nitrogen. Control embryos were also frozen with 1.4 M glycerol+0.25 M sucrose (GLY+SUC). Frozen embryos were thawed in a water bath at 37 degrees C (EG and EG+SUC) or 20 degrees C (GLY+SUC). After thawing the straws containing an embryo frozen in EG, EG+SUC or GLY+SUC were directly mounted into an embryo transfer gun and transferred to recipients without diluting of the cryoprotectants. The pregnancy rates were 69% (20/29), 52% (13/25) and 60% (15/25) for EG, EG+SUC and control medium (GLY+SUC), respectively. The pregnant recipient animals delivered healthy calves except for five which aborted. These results indicated that EG is a suitable cryoprotectant in which to store embryos before they are directly thawed and transferred to recipients.