The age of pronucleate mouse ova influences their development in vitro and survival after freezing

The influence of pronuclear age on embryo development in vitro and on survival and post-thaw development after cryopreservation was investigated. Pronucleate mouse ova were removed from the oviductal environment at three different times: 18 h after human chorionic gonadotrophin (HCG) (just after fertilization), 23 h after HCG (during DNA replication) and 28 h after HCG (just before cleavage). Control ova were either cultured in vitro or transferred in vivo without any treatment or exposed to dimethyl sulphoxide (DMSO) or 1,2-propanediol (PROH) before culture, but without cryopreservation. The effect on survival was evaluated by the development in vitro and in vivo after ultrarapid freezing in 3.5 M DMSO and after slow programmed freezing in 1.5 M PROH. In vitro, the development of control ova to blastocysts was 39, 54 and 77% per treated ovum at 18, 23 and 28 h after HCG, respectively. The survival rate was 78, 92 and 96% after ultrarapid freezing and 69, 90 and 81% after slow freezing, respectively. The subsequent rate of development to blastocysts per survived ovum was 21%, 35% and 62% after ultrarapid freezing and 38, 54 and 63% after slow freezing. In vivo, however, the pronuclear age did not influence the implantation rate or the number of living fetuses per transferred ovum, for neither the control, nor the frozen/thawed ova. The implantation rate and the numbers of living fetuses were not significantly different for frozen/thawed and control ova. In conclusion, early pronucleate mouse ova have a lower developmental capacity in vitro and a lower survival rate after freezing and thawing than pronucleate mouse ova just before cleavage.(ABSTRACT TRUNCATED AT 250 WORDS)