Analysis of factors involved in the in vitro production of bovine embryos

Abstract

Recent progress, briefly reviewed here, has led to utility of bovine in vitro oocyte maturation (IVM), in vitro fertilization (IVF), embryo culture and embryo transfer (ET) technologies in commercial and research endeavors. Undefined conditions incorporating selected serum, hormones and other active agents, and cellular constitutents or their contributions to support the in vitro production (IVP) of bovine embryos have enabled our achievement of IVF (cleavage) of 85% and blastocyst development of 40% of oocytes selected for IVM. Conditions for IVM have profound influence on subsequent events in IVP of embryos. Defined conditions for IVM coupled with semidefined conditions for IVF and cell-free embryo culture enable IVF of 74% and blastocyst development of 28% of immature oocytes selected for IVM. Efforts to understand a pronounced positive influence of LH during IVM on oocyte to blastocyst development in vitro led to recognition of variable hormonal effects on metabolism of bovine oocytes. Thus, LH markedly stimulates glycolysis and the tricarboxylic acid (TCA) cycle while TSH was found to increase glucose oxidation via the pentose cycle and FSH caused no change in metabolism of cumulus-enclosed oocytes (CEOs) in comparison to medium alone. Metabolic activities of CEOs is attributed primarily to the cumulus cells (CCs) but presence of the oocyte is necessary for hormonal responses observed. From ongoing research clues are anticipated to allow further understanding of important mechanisms and for development of improved methodologies for IVP of bovine embryos.