Abstract
Rabbit eggs, with or without folliculai cells, are highly fertilizable in vitro (Fraser et al., ยป71). In vitro aging of intact, cumulusโdevoid, and coronaโdevoid rabbit eggs did not appreciably lower their subsequent fertilizability in vitro with fresh sperm. The intact and cumulusโdevoid eggs were somewhat less fertilizable than the coronaโdevoid eggs when aged for two and oneโhalf hours (70%, 68%, 91%, respectively), but this difference disappeared when the aging period was six hours (83%, 82%, 91%) or 12 hours (83%, 81%, 82%). Chromosome complements ranged from hypodiploid to polyploid in all groups, regardless of time of aging. Viability of embryos from the three groups, as determined by continued cleavage in vitro, was much reduced when compared to that of unaged eggs similarly cultured. There was no observable correlation between ploidy and development in culture; polyploid complements, particularly triploids, were found in both advanced and retarded stages.
The possible effect of aging at an earlier time was noted in studies involving transfer of two to four cell embryos to pseudopregnant recipients. Embryos derived from eggs recovered 13 hours postโLH and fertilized in vitro had low implantation rates and none of the implants developed to full term fetuses. However, the development of embryos from eggs recovered 12 hours postโLH was not significantly different from embryos fertilized in vivo and cultured prior to transfer; 21% and 24%, respectively, of the embryos transferred developed to term.
A number of the offspring have been raised to maturity. Those from the in vivo fertilized embryos have appeared normal and their eggs and sperm have had no obvious defects. From a similar sample size of in vitro fertilized offspring, 2/14 have displayed defects of the limbs resembling a condition termed splayleg, thought to be a recessive genetic trait. Whether conditions of in vitro fertilization might favor the union of two gametes carrying the recessive gene is not known.