CRYOPRESERVATION OF PORCINE EMBRYOS BY VITRIFICATION - A STUDY OF IN-VITRO DEVELOPMENT

Until recently, attempts to preserve porcine embryos have been unsucce ssful. Vitrification has been developed as a method of cryopreserving mammalian embryos by avoiding ice crystal formation, assuring a cryopr eserved glass state during storage in liquid nitrogen. Vitrification m ay be a useful method of overcoming the deleterious effects of chillin g injury when pig embryos are cryopreserved using conventional slow fr eezing procedures. In this study, we applied vitrification procedures for rodent and/or bovine embryos to cryopreserve porcine embryos. Foll owing warming, survival was defined as normal development of embryos i n culture, namely the formation or reexpansion of the blastocoelic cav ity. Experiment 1 tested the relative toxicity of 3 vitrification proc edures on Day-5, 6 and 7 porcine embryos. Embryos equilibrated in vitr ification solution (VS3a) continued to develop in vitro at rates compa rable to that of untreated control embryos. Experiment 2 was designed to evaluate embryonic development following cryopreservation by vitrif ication in VS3a. Day-5 porcine embryos did not survive cryopreservatio n while Day-6 and Day-7 embryos survived and continued development in vitro. In Experiment 3, we evaluated a period of culture prior to vitr ification and its effect on cryosurvivability of porcine embryos. A 3- h culture period prior to vitrification had no effect on cryosurvivabi lity over that of freshly recovered, immediately vitrified embryos. Th ese studies indicate, for the first time, that porcine embryos can be successfully cryopreserved by vitrification based on morphology and su bsequent development in vitro. However, survival following cryopreserv ation appears to depend upon embryonic age or stage of development.