Study On Cryopreservation Of Oocytes And Mechanisms Impacting Post-Warming Developmental Competence In Pig

The cryopreservation of mammalian oocytes increasingly displayed its huge potential of application in animal resource protection. Although various of protocols for oocyte freezing have been developed, most of them were applied in mouse, cattle and human oocyte cryopreservation successfully. To date, cryopreservation of porcine oocytes has not yet made any breakthrough. Suitable protocols used in cryopreservation of porcine oocytes were quite limited. Therefore, it became urgent to establish a high efficient cryopreservation platform for porcine oocytes. In addition, study on the mechanisms of cryotolerance against cryopreservation of porcine oocytes was also limited. In the present study, porcine germinal vesicle (GV) stage and metaphase II (MII) stage oocytes were vitrified with open pulled straw (OPS) method in order to investigate the effects of cryopreservation on their post-warming survival and developmental competence. On the basis of the optimization of freezing protocol, the ultrastructure and cytoskeletal structure of porcine oocytes were investigated systematically so as to enhance the understanding of mechanisms on influencing viability of vitrified porcine oocytes, to furnish a reference for porcine oocyte cryopreservation, and to establish a basis for further improvement of cryopreservation of porcine oocytes. This study contained the following 7 parts.Experiment 1. Collection and maturation in vitro of porcine oocytes. The purpose of the experiment was to optimize the collection and in vitro maturation procedures of porcine oocytes from ovaries acquired in an abattoir. The aspiration method was used to collect oocytes from 2-5 mm and >5 mm follicles in diameter and the cutting method was adopted to collect oocytes from follicles < 2 mm in diameter. The result showed that either total number or average number per ovary of oocytes obtained with cutting method were significantly higher than those from aspiration method (1300 versus 570 and 31.0 versus 13.6, respectively, P<0.05). However, the percentages of available oocytes from cutting method were 33.8%, significantly lower than the percentage of aspiration method (67.5%,...