Abstract
In vitro culture of bovine preimplantation embryos, in general, has been achieved in a serumsupplemented medium with a co- cultivation of somatic cells such as oviduct epithelial cells and cumulus/granulosa cells. This review describes an improved culture methodology of bovine preimplantation embryos that can be cultured in a serum- free medium without somatic cell support. Several improvements have been undertaken to establish a novel serum- free culture system in order to increase the efficiency of bovine embryo development. The optimal energy utilization of embryos was determined with a reduced concentration of glucose from a commercial nutrient TCM199 medium and added with pyruvate and lactate. Oxygen tension is one of critical factors in culture environment. Low oxygen concentration (5% O2) was superior to the regular open air culture system (approximately 20% O2) for bovine embryo development. Polypeptide factors such as FGF-2, TGF-β1 and tissue inhibitor of metalloproteinase-1 (TIMP-1) were identified as embryotrophic activity. As a result, the newly developed serum- free culture system without somatic cell co-culture apparently increased the higher efficiency of bovine blastocyst formation than conventional serum- supplemented medium with somatic cells.
