This study was designed to examine the effect of the age of rabbit oocytes on the developmental potential of cloned embryos. The metaphase II oocytes used for nuclear transfer (NT) were collected at 10, 12, 14, and 16 h post-hCG injection (hpi). The total number of oocytes collected per donor (21.4-23.7) at 12 to 16 hpi was similar, but significantly higher than that collected at 10 hpi (16.2). Additionally, a significant improvement in blastocyst development was achieved with embryos generated by electrically mediated cell fusion (56.0%), compared to those from nuclear injection (13.1 %) (Experiment 1). Markedly higher blastocyst development (45.8-54.5%) was also achieved with oocytes collected at 10-12 hpi than from those collected 14-16 hpi (8.3-14.3%) (Experiment 2). In Experiment 3, the blastocyst rates of NT embryos derived from oocytes harvested 12 hpi (39.2-42.8 %) were significantly higher than from those collected at 16 hpi (6.8-8.4 %) (p < 0.05), regardless of the donor cell age. Kinase activity assays showed variable changes of activity in rabbit oocytes over the period of 10-16 hpi; however, there was no correlation with preimplantational development (blastocyst rate vs. MPF, R = 0.326; blastocyst rate vs. MAPK, R = -0.131). Embryo transfer of NT embryos utilizing 12 hpi oocytes resulted in one full-term but stillborn, and one live cloned rabbit; thus, an efficiency of 1.7 % (n = 117) (Experiment 4). These results demonstrated that NT utilizing relatively young rabbit oocytes, harvested at 10-12 h after hCG injection, was beneficial for the development of NT embryos.

This study was conducted to determine the effect of rabbit oocytes collected from ovaries or oviducts on the developmental potential of nuclear transplant embryos. Donor nuclei were obtained from adult skin fibroblasts, cumulus cells, and embryonic blastomeres. Rabbit oocytes were flushed from the oviducts (oviductal oocytes) or aspirated from the ovaries (follicular oocytes) of superovulated does at 10, 11, or 12 h post-hCG injection. The majority of collected oocytes were still attached to the sites of ovulation on the ovaries. We found that follicular oocytes had a significantly higher rate of fusion with nuclear donor cells than oviductal oocytes. There was no difference in the cleavage rate between follicular and oviductal groups, but morula and blastocyst development was significantly higher in the follicular group than in the oviductal group. Two live clones were produced in follicular group using blastomere and cumulus nuclear donors, whereas one live clone was produced in the oviductal group using a cumulus nuclear donor. These results demonstrate that cloned rabbit embryos derived from follicular oocytes have better developmental competence than those derived from oviductal oocytes.

Background Dual/double stimulation (DS) is an ovarian stimulation strategy that has emerged in recent years; it is characterized by two rounds of ovarian stimulation and oocyte retrieval in the same menstrual cycle. DS can greatly shorten the time required to obtain valid embryos in assisted reproduction. For fertility preservation, DS can speed up oocyte storage process. However, factors influencing luteal phase ovarian stimulation (LPS) outcomes in DS have not been elucidated. Methods A total of 156 cycles from 78 cases were studied. Patients were grouped and analyzed according to their follicular phase ovarian stimulation (FPS) types. Female ages, ovarian stimulation protocols, number of oocytes retrieved, embryo quality were recorded. Comparisons of outcomes were conducted between different groups. Results Our study found that LPS obtained similar outcomes to follicular phase stimulation (FPS), and that the choice of FPS protocol affected the efficiency of LPS, the antagonist protocol and progestin-primed ovarian stimulation (PPOS) protocol resulted in better embryo outcomes in LPS. In LPS of DS, sufficient stimulation duration was the guarantee of embryo quality (number of available embryos: β = 0.145, 95% CI [0.078–0.211], P = 0.000; number of high-quality embryos: β = 0.114, 95% CI [0.057–0.171], P = 0.000). Discussion This study provided ideas for the precise use of DS. We suggest to further expand the sample size of DS in the future, conduct prospective controlled studies, unify the sample size of each subgroup, include the ovarian reserve of patients in the grouping basis, and exclude the influence of male factors. We hope that this study will help further refinement of DS so as to maximize patient benefits from it. Conclusion When the DS strategy is considered in the follicular phase, the antagonist protocol and PPOS protocol are more recommended for better embryo outcomes in LPS. During LPS, adequate ovarian stimulation duration is the most important guarantee for LPS efficiency.