Morphological and physiological differences between in vivo- and in vitro-produced preimplantation embryos from livestock species

Abstract

Almost fifty years have passed since 1949 when Dowling (14) used an egg-saline medium, developed by Hammond (26) for mouse embryos to culture 8-cell bovine embryos to the 16-cell stage. These investigators certainly must have queried the normality of the cultured embryos with their variations in cell shape and color observed. With the advances of in vitro systems and the improvement of instrumentation, investigators are faced with the same fundamental questions asked some fifty years ago. Namely, how viable are embryos that are manipulated in vitro, as compared to embryos in vivo? Compounding this difficult question is the lack of basic information on metabolic processes of in vivo embryos. Once the embryos are removed from the maternal environment for study, they are exposed to myriad in vitro conditions which can negatively effect metabolism or morphology. This manuscript is a review of the literature concerning studies that compared in vitro-manipulated to in vivo-produced preimplantation embryos from the farm species. The authors apologize in advance for studies which were inadvertently omitted and acknowledge the diligent work of investigators who have published in this most challenging and important area of embryo development.