Successful embryo transfer of cryopreserved and in-vitro fertilized rabbit oocytes

In-vitro fertilization experiments with frozen/thawed rabbit oocytes were performed to develop an effective technique to be used for the in-vitro fertilization of cryopreserved human oocytes. Ovulatory oocytes, collected from the oviduct of virgin does 13 h after induction of ovulation by HCG injection, were cryopreserved slowly to -30 degrees C and plunged directly into liquid nitrogen. A mixture of 1.5 M 1,3-propanediol and 0.1 M sucrose was used as a cryoprotectant. After thawing, the oocytes were incubated with in-vitro capacitated sperm for 5 h in defined Brackett's medium. Fertilized ova were cultured for an additional 20 h until the 4-to-8-cell stage was reached. These embryos were transferred to pseudopregnant recipient rabbits which were 'asynchronous' in the sense that they had been given an injection of HCG 30, 24 and 18 h before starting to do the embryo transfer. A 32% survival rate of frozen/thawed oocytes was achieved. The fertilization rate was 74% (181/264) in this study. A total of 53 embryos was transferred to the oviducts of six recipients of three different asynchronicity and four young were born. The highest implantation rate (including resorptions) of 18% could be achieved in this investigation by using -6 h asynchronous recipients, while the overall implantation rate was 9.4%.