Both Male and Female Pronuclei Formation in Canine Oocytes Inseminated at Germinal Vesicle Stage

Abstract

In the dog, copulation can occur 2-3 days before ovulation and oocytes are ovulated at the stage of the germinal vesicle (GV). It is therefore probable that GV oocytes can be penetrated by spermatozoa and developed normally. In the present study, we examined the penetration rate and male and female nuclear changes in canine oocytes which were inseminated just after collection from preovulatory follicles and cultured for up to 72 h. The penetration rate reached its maximum (64.4%) at 24 h after insemination, although only 6.9% of penetrated oocytes were mature at that time, indicating that GV oocytes were penetrated by spermatozoa. Thereafter, the maturation rate increased to 17.9% and 60.0% of penetrated oocytes at 48 and 72 h after insemination, respectively. Both male and female pronuclei were developed in 26.7% of matured-fertilized oocytes at 72 h after insemination. These results suggest the possibility of the participation of GV oocytes in the normal fertilization processes in the dog.