In vitro culture and embryo metabolism of cattle and sheep embryos - a decade of achievement

At the beginning of the 1990s, co-culture of cattle and sheep embryos was t he most favoured method to support embryo development, but the use of this system has hampered prepress in raising the efficiency of embryo production . Furthermore, little was known of the requirements of embryos and the bioc hemistry of early embryo development. As the decade progressed, energy meta bolism studies improved our understanding of the energy substrate requireme nts for embryo development. Furthermore, an appreciation of the reproductiv e tract environment increased. This resulted in more "defined" systems, whi ch have evolved further in the development of "sequential" media systems, w here components change in accordance to the needs of the embryo. Neverthele ss, wholly defined systems, such as the replacement of albumin with PVA, ar e less able to support similar levels of development as protein-containing medium, and the resulting embryos are metabolically compromised. This highl ights the nutritive role of albumin. One area in which much work has been c onducted, but yet no unifying theory has emerged, is that of the interactiv e roles of growth factors (including autocrine/paracrine), cytokines and ex tra-cellular matrix molecules in the development of a viable embryo. A new concept is that of regulation of energy metabolism. Compounds such as ethyl enediamine tetraacetic acid (EDTA), NaN3 and 2,4-dinitrophenol have been sh own to increase embryo development and quality of resulting embryos. This d emonstrates that the process of ATP production is a key regulator of in vit ro embryo development. (C) 2000 Elsevier Science B.V, All rights reserved.