Ovulation, fertilization and preimplantation embryonic development in raccoon dogs (Nyctereutes procyonoides)

- The ovulation time and the developmental kinetics of embryos in vivo were determined in the raccoon dog.
- Prior to the 4-cell stage, the embryos were located in the oviduct, while they had moved into the uterus at 16-cell stage in the raccoon dog.
- Heterogeneity in developmental process and asynchronous cleavage were observed within the cohort of embryos collected from the same female.

A study involving 32 sexual mature females was conducted to characterize ovulation, fertilization and early embryonic development in vivo in raccoon dogs. Oocytes and embryos were collected from the oviducts and uteri, evaluated by stereomicroscopy. Ovulation occurred 25-32 h after a female first accepted mounting, regardless of copulation, when the females were paired with a male in the same cage. Ovulated oocytes were at the primary stage. The number of ovulated eggs in females with or without mating was 9.96 ± 2.65 and 9.00 ± 1.92, respectively. Embryos at 2-4 cell, 8-16 cell, morula, blastocyst, and hatched blastocyst stage were observed at 29-73, 48-100, 98-126, 169-198 and 217-268 h after first mating, respectively. Embryos were located in the oviduct prior to 4-cell stage and moved into the uterus after 16-cell stage. Embryos at different stages were often obtained from the same female. During the zygote underwent a series of cleavage divisions, the diameter of the embryo cell mass continuously increased through the 2-cell and 4-cell stage, then started to decrease and was the minimum size at the morula stage. At the blastocyst stage, embryos increased in volume, and finally developed into a hatching blastocyst with a thinner zona pellucida. This is the first full report of preimplantation embryonic development in the raccoon dog, which will facilitate the application of advanced assisted reproductive technology in canine species.