Ultrastructure and Development of Vitrified/Warmed Bovine Oocytes Matured with 9-cis Retinoic Acid

In this work we analyze the effects of vitrification on the ultrastructure and developmental ability of bovine oocytes matured in the presence of 9-cis-retinoic acid (RA). Bovine cumulus oocyte complexes (COCs) were matured in a basic medium containing 10% fetal calf serum (FCS), 9-cis-RA or polyvinyl alcohol (PVA). Mature oocytes were vitrified using the Open Pulled Straw method with minor modifications. A group of fresh and vitrified/warmed COCs was fixed for ultrastructural analysis, while the remaining oocytes were fertilized in vitro and cultured. Vitrification of mature oocytes produced high rates of degeneration regardless of the in vitro maturation protocol and low number of cleaved embryos. Development rates up to day 8 were similar between groups undergoing vitrification, which were lower than fresh controls. Morphologic alterations were observed in all groups of vitrified oocytes, although in vitro maturation in the presence of 9-cis-RA combined with vitrification led to higher ultrastructural damage. More research is needed to explain the low survival rates of the bovine oocyte after vitrification and warming.