DEVELOPMENT OF FROZEN-THAWED PORCINE BLASTOCYSTS IN-VITRO AND IN-VIVO

Cryopreservation of porcine embryos would greatly facilitate the maint enance of genetic resources and the practical application of embryo tr ansfer programmes. In this study, the effect of the stage of developme nt of porcine embryos (pre-hatch vs post hatch) on the post thaw viabi lity of blastocysts was evaluated, The blastocysts had been recovered from superovulated donor gilts and frozen in 1.5M glycerol according t o a standard slow cooling protocol, From 444 frozen-thawed embryos, 30 2 (68 per cent) were judged to be viable and were used for a 24-hour c ulture experiment in modified Whitten's medium (n=89) or transferred t o three synchronous (n=72) or seven asynchronous (-24 hours) recipient s (n=141). The proportion of embryos surviving in culture was signific antly (P=0.05) greater for those frozen as post hatch (17/34) than as pre-hatch blastocysts (8/36). Although transfer of frozen-thawed embry os to synchronous recipients did not result in a pregnancy, two of the asynchronous recipients, which received 15 and 22 embryos, became pre gnant and farrowed five and three piglets, respectively, at normal ter m, In spite of the overall inefficiency of the cryopreservation proced ure used in this study, the birth of piglets from two successful trans fers of frozen-thawed blastocysts suggests that further study of the c ryopreservation protocols would be worthwhile.