Preimplantation development of cloned canine embryos recovered by hysterectomy or surgical uterine flushing and subsequent pregnancy outcomes

Dog cloning offers a substantial potential because of the advancements in assisted reproductive technology and development of the human disease model in line with the transgenic technique. However, little is known about the development of the canine cloned embryo during the preimplantation period. The aim of this study was to investigate the most efficient method and time for collecting cloned canine preimplantation embryos and to ascertain the developmental timeline of cloned canine embryos. Two hundred cloned embryos were created and transferred into 11 surrogates. The preimplantation stage cloned embryos were then collected on Days 7, 8, and 9 using an ovariohysterectomy or the Foley balloon catheter method. The recovery rate of reconstructed embryos was 63.6% and 60.6% for the ovariohysterectomy and Foley balloon catheter methods, respectively. Although significant differences were observed in the early developmental stages (one-cell and 16-cell stages), no significant difference was observed in the blastocyst stage. Significantly higher blastocyst rate was observed when the embryos were collected on Day 8 (11.4%) than on Day 7 (0.0%; P < 0.05). At the proximal uterine horn on Day 7, no embryos at any stage were found, whereas on Days 8 and 9, blastocysts were found. We have observed a 63% initial pregnancy rate at 25 to 30 days after embryo transfer and a 50% full-term pregnancy rate, whereas 6.3% of the puppies were born, and 5.5% were born live among the total transferred embryos. Our results suggest that cloned embryos can develop to blastocysts by Day 8, and full-term pregnancy can be achieved after embryo transfer in canine.