Effect of different oocyte retrieval and culture methods on in vitro maturation of bovine oocytes derived from vitrified ovarian tissue slices

In a successful method of ovarian tissue cryopreservation, there are always a number of antral follicles remain intact, as a result of which the methods of retrieving and culturing oocytes from them becomes very important. Therefore, this study aimed to obtain an efficient method for oocyte retrieving and maturation in vitro from vitrified/warmed ovarian tissue slices. For this purpose, slaughterhouse-derived bovine ovaries were sliced and prepared in six replicates for each segment of each experiment and vitrified at 4? and room temperature (RT) by 1.8 ml cryovial. After warming, the oocyte-cumulus complexes (COCs) were retrieved by two methods (aspiration and slicing), and matured in vitro in two conditions (in the presence or absence of oviductal epithelial cells (OECs) as feeder cells) for 24-48h, and finally, the nuclear maturation of oocytes was evaluated as the statistical analysis showed the higher degeneration rates of oocytes derived from vitrified ovarian tissue in aspiration groups (P<0.05) and the more M-II stage oocytes were obtained in the slicing groups (P<0.05), although the aspiration method was better to approach for oocyte retrieval from fresh ovarian tissue than slicing method (P<0.05). Also, the exposure temperature in the vitrification procedure of ovarian slices did not affect the percentage of M-II oocytes in the evaluated groups. It can be concluded that the slicing method is a more proper approach for oocyte retrieval from vitrified ovarian tissue than an aspiration, and the use of co-culturing of these immature oocytes with OECs during IVM is not required.