INCREASING THE RATE OF BLASTOCYST FORMATION AND HATCHING FROM IN VITRO-PRODUCED BOVINE ZYGOTES

This study was designed to identify parameters that would facilitate e arly selection of superior embryos, as well as to define culture condi tions that could increase the proportion of embryos proceeding to the blastocyst stage. In the first experiment, the developmental potential of bovine embryos that had reached different stages of development af ter 60 h of culture following insemination was assessed. No 2-cell emb ryos underwent further cleavage. Of the 4-cell embryos (n=188) only 12 .2% progressed to the blastocyst stage, while 62.5% of 8-cell embryos (n=480) did so (P<0.01). In a further experiment, the effects of condi tioning the culture medium (TCM 199) either with Buffalo rat liver cel ls (BRLC) or bovine oviductal epithelial cells (BOEC) and the effects of co-culture with either of these 2 cell types were examined. The per centage of 8-cell embryos proceeding to the morula and blastocyst stag es was independent of cell type and culture system. However, BOEC-cond itioned medium supported significantly lower production of blastocysts than any of the other culture methods. Only 24.1% of the former proce eded to the blastocyst stage after the full 10 d of culture, and only 3% hatched, values that were significantly lower than in the other 3 g roups (P<0.01). Among the latter, 44% progressed to the blastocyst sta ge in BRLC-conditioned medium while 44 and 46% reached that endpoint a fter co-culture with BOEC or BRL cells, respectively. The percentages that hatched among these were 28.2, 31 and 28.5%, respectively.