Improvements to in vitro culture media for use in bovine IVF

In assisted reproduction of cattle the design and preparation of in vitro culture media has been instrumental in supporting the development of bovine oocytes and embryos. In vitro production (IVP) involves three main sequential steps: oocyte aspiration and in vitro maturation (IVM); in vitro fertilization (IVF); and in vitro culture (IVC) of early pre-implantation embryos. Research on IVC media has aimed to emulate the crucial elements that are present in the oviduct and uterus of female cattle by supplementing with protein and growth factors. As a result, IVP has proven a reliable methodology with an acceptable, if far from remarkable, blastocyst transfer rate of typically 40%. Moreover, the addition to media of defined extracts has gradually replaced that of fetal calf serum, leading to improved embryo viability and cryotolerance. Nevertheless, major advances in the composition of novel media that may facilitate a further increase of blastocyst rate have yet to be realized. Currently, there is considerable variation in the constituents of IVC media used in bovine assisted reproduction. Hence, significant innovations are required in order to not only achieve a greater success rate of IVP and to enhance the cryotolerance of bovine IVF-derived embryos but also to provide a defined IVC medium that may be recognized as a point of reference across the cattle breeding industry. This review examines the progress made to date in IVP to enhance embryo quality and points to future areas for investigation of a ‘gold standard’ IVC medium. This is a fully defined medium that supports consistently the attainment of a bovine IVP blastocyst rate similar to that achieved using a conventional medium supplemented with serum.