In vitro aging of porcine oocytes

Abstract

Porcine oocytes matured in vitro develop in various ways if they are further cultivated. In our studies these oocytes were cultivated for 1 to 5 days (in vitro aging). During the 1st day of aging, most of them remained at the stage of metaphase II (98%). Then many oocytes underwent the spontaneous parthenogenetic activation. The portion of activated oocytes reached its peak after 2 or 3 days of aging in vitro (39 or 45%). The portion of fragmented oocytes peaked at the same time (28%). During subsequent aging in vitro (i.e. day 4 or 5 of aging), the portion of lysed oocytes significantly increased (30 or 37%). The highest portion of spontaneously activated parthenogenetic embryos at a pronuclear stage (35%) was observed during the 2nd day of aging in vitro. These pronuclear embryos had mainly one polar body with two pronuclei (47% of all pronuclear embryos) or two polar bodies with one pronucleus (38% of all pronuclear embryos). During the 3rd and 5th day of in vitro aging, there was a significant increase in the portion of parthenogenetic embryos cleaved to the 2-cell or 3-cell stage. When considering the prolonged in vitro culture of porcine oocyte, only the first day of aging should be taken into account, since beyond this time significant changes, i.e. parthenogenesis, fragmentation or lysis, occurred in oocytes under in vitro conditions.