Noninvasive bovine oocyte quality assessment: possibilities of a single oocyte culture

Although bovine embryos are routinely produced in vitro for several decades, there still exists a critical need for techniques to accurately predict the oocyte's developmental competence in a noninvasive way, before the in vitro embryo production procedure. In this review, several noninvasive methods to evaluate oocyte quality are discussed, such as morphological assessment of the cumulus oocyte complex and the use of brilliant cresyl blue. Because an individual oocyte and embryo culture method can possibly generate additional insights into the factors that determine oocyte quality, the second part of this review summarizes the state of the art of bovine single oocyte culture. The optimization of individual in vitro embryo production can obviously accelerate the quest for better noninvasive oocyte quality markers, because more information about the oocyte's requirements and intrinsic quality will be revealed. Although each step of in vitro culture has to be re-examined in light of the hampered production of single embryos, the reward at the end will be substantial. Individual scored oocytes will be traceable along the in vitro embryo production procedure and the final blastocyst outcome can be linked to the original oocyte quality and follicular environment without the bias caused by simultaneously developing embryos.