Can embryo metabolism be used for selecting bovine embryos before transfer?

The quality of in vitro-produced bovine embryos remains variable. The selection of these embryos based only on their morphology does not allow for acceptable gestational rates to be obtained. The use of metabolic markers to select viable embryos before transfer would be of valuable help, both economically and as a research tool. The ideal marker should meet several conditions: it should be able to be evaluated 1) in a totally non-invasive manner, 2) on individual embryos (which necessitates very sensitive techniques), 3) very rapidly (so that it is compatible with the immediate transfer of fresh embryos), and 4) in order to allow viable embryos to be separated from those that are not viable, whatever the production system used. In practice, such a marker does not exist, but certain methods of metabolic evaluation resemble it. The development of a metabolic marker is confronted by the metabolic characteristics of the embryo, notably the evolution of the metabolism during the development of the embryo and its adaptation to the changes in the environment. (C) Inra/Elsevier, Paris.