EFFECT OF GLUCOSE ON EMBRYO QUALITY AND POSTTHAW VIABILITY OF IN-VITRO-PRODUCED BOVINE EMBRYOS

The present study was carried out to evaluate the effect of glucose ab sence during the first 24 h of culture on blastocyst quality and survi val after freezing and thawing. In Experiment 1, IVM/IVF bovine zygote s from a slaughterhouse were cultured for 24 h in SOFm, either in the absence or in the presence of 1.5 mM glucose and then further cultured for 7 d in SOFm with 1.5 mM glucose. Absence of glucose during the fi rst 24 h of culture increased (P < 0.001) the percentage of embryos th at developed to the morula and blastocyst stages. In Experiment 2, pre sumptive zygotes were incubated for 24 h in the absence of glucose and were then cultured for 7 d in the presence of 1.5, 3 or 5 mM glucose. There were no differences in the percentages of embryos developing to morula or blastocyst stages at 1.5 or 3 mM glucose, whereas the 5 mM concentration appeared to be detrimental (P < 0.001). Blastocysts from Experiments 1 and 2 were assessed for freezing resistance by means of the ability of frozen-thawed embryos to re-expand their blastocoelic cavity and hatch after culture for 72 h in vitro. For Grade 1 and 2 bl astocysts, the post-freezing survival rate was unaffected when glucose was omitted during the first 24 h of culture, provided that the gluco se was subsequently maintained between 1.5 and 3 mM. At 5 mM glucose, blastocoelic re-expansion was inhibited (P < 0.03). Addition of 1.5 or 3 mM glucose to the culture medium following 24 h of culture without glucose did not affect embryo cell number, whereas 5 mM significantly decreased it (P < 0.01). These results indicate that the first 24 h of culture without glucose do not affect embryo quality or post-thaw via bility, but an increase in blastocyst yield was observed. After 24 h o f culture addition of glucose in the range 1.5 to 3 mM was beneficial, while as higher concentrations decreased the efficacy of this in vitr o production technique. (C) 1997 by Elsevier Science Inc.