Gliding into diapause: early embryo development in roe deer (Capreolus capreolus)

During mammalian diapause, the embryo is arrested at the blastocyst stage. In diapausing carnivores and marsupials, growth arrest of the blastocyst is coincident with a quiescent corpus luteum (CL). In the roe deer, progesterone is produced throughout diapause and the blastocyst exhibits very slow growth. To date, early roe deer embryos of known age have not been described. Therefore, it is not known at which stage and at what pace the roe deer embryo enters diapause. To collect multiple embryos of known gestational age, we performed cycle synchronization and superovulation in captive roe deer prior to artificial insemination (AI) and natural breeding (NB), respectively. Superovulatory responses were evaluated based on ultrasonographic detection of CL formation on the day of in vivo embryo flushing and on plasma progesterone (P4) analysis. In total, 33 superovulation treatments resulted in 6.6 ± 2.2 (mean ± SD) CL per doe on the day of embryo flushing. At days 6 and 7 after AI, 37 multicellular embryos up to the morula stage were retrieved from 8 does. At day 12 and 13 after natural breeding, 28 embryos, mainly at the blastocyst stage (n=20), were collected from 7 does. Multiple embryos could be collected from single animals, proving the feasibility of superovulation in this species. Compared to other diapausing and non-diapausing species where blastocysts have formed at days 6 – 8, roe deer embryo development appeared to be already decelerated prior to the blastocyst stage. The roe deer might therefore be well suited as a model to investigate mechanisms regulating embryonic growth velocity with respect to cell cycle control