Development of bovine embryos in vitro following oocyte maturation under defined conditions.

A total of 4,615 immature bovine oocytes were used in a series of experiments aimed at the systematic evaluation of the role of the different components of our in vitro maturation (IVM) medium in imparting developmental competence to the oocytes. The results clearly demonstrate that both tissue culture medium 199 (M199) and synthetic oviduct fluid (SOF) are capable of supporting the IVM of bovine oocytes at high rates in the absence of macromolecular supplements, as evidenced by subsequent development to the blastocyst stage (20 and 25%, respectively). However, both were significantly lower than the control (containing 10% fetal calf serum, 5 micrograms/ml pLH (porcine luteinizing hormone), 1 microgram/ml pFSH (porcine follicle-stimulating hormone), and 1 microgram/ml-17 beta-estradiol, E2) in terms of blastocyst yield. Inclusion of bovine serum albumin (3 mg/ml) was not beneficial and in fact significantly depressed development when added to SOF. It was shown that the advantage of the control conditions over unsupplemented M199 and SOF was entirely attributable to the presence of serum and that in the absence of serum the inclusion of the above hormone cocktail significantly depressed postcleavage development. When used individually, neither LH (50, 500, 5,000 ng/ml) nor FSH (10, 100, 1,000 ng/ml) improved development over M199 alone. In conclusion, we now have a simple maturation system, using a fully defined medium (M199) in which the search for factors improving the cytoplasmic competence acquisition of maturing cattle oocytes will be possible.