Luteal contribution to the termination of preimplantation delay in mink

Five groups of mink were mated once between March 17-19 (Day O), Group 1, designated intact controls, received no further treatment. The remaining four groups of mink underwent unilateral ovariectomy on the day following mating. At that time, preovulatory follicles were transplanted to the ipsilateral kidney capsule of two groups (3 and 5) to become ectopic corpora lutea (CL). The second ovary was removed from all of the animals in Groups 2-5 on Day 8 after mating. At that time animals in Groups 4 (ovariectomized) and 5 (ovariectomized + ectopic CL) received 1-g Silastic implants releasing progesterone. Similar Silastic implants without progesterone were administered to Groups 2 (ovariectomized only) and 3 (ovariectomized + ectopic CL). Blood samples were taken for progesterone analysis and laparotomies performed on all mink through Day 44 of the experiment. Embryos implanted in all (7/7) of the animals in Group 1 (intact controls) at an average of 23.7 days after mating. In Group 5 (ectopic CL + progesterone implant) 6/8 mink were found to have embryos which were calculated to have implanted at an average of 36.3 days after mating. No embryo implantation occurred in Groups 2, 3 and 4 although some unattached blastocysts were recovered from the uteri of the latter two groups. Progesterone was elevated by implants to levels typical of mink gestation. Ectopic corpora lutea further increased progesterone levels in the presence of a progesterone-releasing Silastic implant. The results demonstrate the absolute necessity of the ovary for embryo implantation in mink. Further, the hormonal requirements for implantation consist of progesterone as well as some other factor or factors of luteal origin.