An experiment was designed to examine factors influencing the efficiency of the direct transfer of frozen/thawed embryos without the need to remove the embryos from straws. The viability of embryos was evaluated by in vitro culture and implantation (in vivo) under field conditions in this experiment. The effect of developmental stages and quality of embryos on survival was also examined. Embryos were recovered from superovulated cows and heifers on days 6, 7 and 8 after oestrus and were grouped on the basis of developmental stages and quality. The only differences between experimental and control embryos were in the method of filling the straw and of the extraction of cryoprotectant after thawing. Embryos were equilibrated for 20 minutes in PBS containing 10% of glycerol and 10% of fetal calf serum (FCS). After equilibration, embryos were aspirated into 0.25 ml artificial insemination straws at room temperature then placed into the freezing machine precooled to -7°C. The embryos in PBS medium containing glycerol were aspirated into straws followed by a small bubble and then by 1.0 M sucrose solution. The ratio of the two solutions was 1:8-10. After 10 min. at -7°C ice crystals were induced and after another 10 min., straws were cooled at 0.5°C/min. to -30°C. At that temperature, the straws were placed into liquid nitrogen. Straws were thawed at room temperature on air for 2 min. Glycerol was removed from the control embryos outside the straws in a 1.0 M sucrose solution. Glycerol was extracted from experimental embryos inside the straws by mixing the glycerol and sucrose solutions for a period of 10 min. Embryos were then either transferred into day 6 to 8 recipients or were placed into PBS+25% of FCS solution at 38 to 39°C for 24 hours in vitro cultures. Significant differences were not found between in vitro cultures of experimental and control groups of embryos in the compacted morulae/early blastocyst stage of development (experimental 80/104, 76.9%; control 52/63, 82.5%). Survival rate of expanded blastocysts was 42% (5/12) for experimental and 53% (17/32) for control embryos (Table 1). The developmental rate for poorer quality of embryos at the compacted morulae and early blastocyst stages were 26% (4/15) for experimental and 23% (4/17) for control groups (Table 2). After transcervical transfer of 42 experimental and 55 control embryos, the respective results of pregnancy rate were 38 (16/42) and 56% (31/55, Tables 3 and 4). The results have suggested that the direct transfer method using sucrose in the straw can be applied with good results in the practice. However, results have to be improved, especially for poorer quality embryos.
|Translated title of the contribution||Practical experiences on frozen bovine embryos transferred just after thawing|
|Number of pages||3|
|Journal||Magyar Allatorvosok Lapja|
|Publication status||Published - Dec 1 1996|
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