COMPARISON OF DEVELOPMENT OF PIG ZYGOTES AND EMBRYOS IN SIMPLE AND COMPLEX CULTURE MEDIA

The development of pig zygotes and embryos in three culture media was investigated. Zygotes and morulae, recovered from superovulated prepub ertal gilts after slaughter, were randomly allocated to culture in one of three simple media: (i) Chatot, Ziomek, Bavister medium (CZB) in 5 % CO2:95% air; (ii) Hepes-buffered CZB medium (H-CZB) in 100% air; or in a complex solution enriched with vitamins and amino acids; or (iii) modified Eagle's minimal essential medium (Pig-MEM) in 5% CO2:95% air . The relative effectiveness of the various media and gas combinations was assessed by determining the percentage of zygotes and morulae tha t developed into blastocysts and hatched from their zonae, as well as by the mean number of cells per embryo. Of zygotes cultured either in CZB in CO2:air, or in H-CZB in air alone, 65% and 57% developed into b lastocysts, respectively; no zygotes cultured in Pig-MEM in CO2:air de veloped beyond the four-cell stage. After 115 h of culture, embryos re sulting from zygotes cultured in either CZB or H-CZB contained approxi mately 50 cells per embryo. Morulae differed from zygotes in their dev elopmental potential in the three media in that virtually all morulae cultured in CZB, H-CZB or Pig-MEM developed to the expanded blastocyst stage in vitro. However, of blastocysts resulting from morulae cultur ed in Pig-MEM, 97% hatched from their zonae, whereas only 8% and 5%, r espectively, of those resulting from morulae cultured in CZB or H-CZB did so. Furthermore, those blastocysts that developed from morulae in Pig-MEM contained significantly more cells than did embryos cultured i n either CZB or H-CZB. More than 60% of 80 zygotes cultured in simple media without glucose developed into expanded blastocysts, but < 30% h atched. In contrast, greater than or equal to 70% of 40 zygotes first cultured in CZB or H-CZB to the morula stage and then placed into Pig- MEM hatched from their zonae. After being held briefly in H-CZB, 42% o f 91 embryos transferred into four of five recipients that became preg nant developed into fetuses or live young.