Effects of centrifugation and lipid removal on the cryopreservation of in vitro produced bovine embryos at the eight-cell stage.

The effects of intracellular lipid polarization and lipid removal treatments on the postthawed in vitro development of frozen bovine embryos at the 8-cell stage were studied. As the first step, bovine presumptive zygotes were centrifuged at 16,000 g for 20 min for the cytoplasmic lipid polarization and their lipid layers were removed by micromanipulation in order to examine the influence of these treatments on the developmental capacity of bovine zygotes. As the second step, bovine embryos developed to the 8-cell stage following centrifugation treatment at various forces (8000, 12,000, and 16,000 g) or lipid removal treatment at the 1-cell stage were frozen in 1.8 M ethylene glycol + 0.05 M trehalose supplemented with 5% polyvinylpyrrolidone in a one-step procedure. There were no significant differences among the control (nontreatment), lipid-polarized, and lipid-removed groups with respect to the developmental capacity of fresh nonfrozen zygotes (experiment 1). The rates of survival and development to the blastocyst of frozen-thawed 8-cell embryos increased slightly with increasing force of centrifugation (experiment 2). The rate of development into blastocysts of the frozen-thawed 8-cell embryos was significantly higher in the groups that underwent centrifugation (at 16,000 g for 20 min; P < 0.05) or lipid removal (P < 0.01) treatments than the control (intact) group. However, there were no significant differences among the groups with respect to the rate of development to the expanded/hatched blastocyst stage. In addition, the mean cell numbers of embryos developed into blastocysts (day 8) derived from frozen-thawed 8-cell embryos tended to be low in the centrifugation and lipid removal groups compared to the controls (experiment 3). These results suggest that although the centrifugation with or without lipid removal treatments has no detrimental effects on the developmental capacity of bovine zygotes, the freezing tolerance of bovine 8-cell embryos was not improved by these treatments.