Abstract
The aim of this study was to characterise embryonic diapause (eD) in the roe deer using
modern techniques of assisted reproduction, especially embryo transfer.
Techniques established in domestic cattle such as synchronisation and superovulation of
embryo donors and recipients, recovery and transfer of embryos and techniques for the
genetic allocation of parentage were applied to this wildlife species for the very first time.
The results of synchronisation, superovulation, recovery and transfer of embryos and their
meaning for the embryonic diapause in roe deer are summarised as follows: (A) Application
of intravaginal gestagene sponges resulted in the synchronisation of all embryo donors.
After removal of the sponges, all animals came into oestrus and mated. (B) Under protection
of the artificial luteal phase created by the vaginal sponges, it was possible to superovulate
the females by injection of ECG followed by subsequent antagonisation with anti-ECG.
Transrectal adaptersonography made it possible to monitor ovarian dynamics and to
quantify the number of dominant follicles, respectively the number of corpora lutea.
Significantly higher numbers of corpora lutea and significantly higher numbers of recovered
embryos in combination with higher values of progesterone in the superovulated animals
compared to the non-superovulated animals as well as satisfying rates of ovulation of 70 %
on average lead to the conclusion that hormone regimes with ECG/anti-ECG are suitable for
the superovulation of roe deer. (C) Due to the anatomy of the reproductive tract of female
roe deer, embryos could not be recovered non-surgically although insertion of the catheter
into the uterine lumen was possible. The results of the surgical flushing of each uterine horn
resulted in recovery rates of 41 % on average (relation of the number of embryos to the
number of corpora lutea), which is satisfying and comparable to the results reported from
other Cervidae. Compared to the recovery rate of embryos reported for domestic species
like goat and sheep the surgical flushing of embryos in roe deer was less successful. (D)
Flushing of embryos on estimated days 7 and 9 of cycle brought up embryos in a wide
variety of developmental stages. All of those early developmental stages were found in the
uterine horns and not in the oviducts. It was concluded that embryonic development in roe
deer is delayed immediately after conception. (E) Application of PGF2a to synchronise
cycles in six of eight recipients during diapause resulted in a measurable decrease of
progesterone in the faeces followed by a return back to the starting point. Parallel to these
findings it was possible to monitor the regression and the development of new corpora lutea,
being at their prime on the day of embryo transfer. (F) After embryo transfer in autumn,
three of eight females became pregnant (one of them carrying twins). Two pregnancies
could be diagnosed in January shortly after implantation using transrectal ultrasonography.
All of the pregnant females had been synchronised with the age of the embryo transferred,
there was no pregnancy in the non-synchronised females. Although fawns were born at the
pysiological time for roe deer births the hypothesis of an artificially shortened diapause could
not be verified. Blood samples taken from all members of the three roe deer families for the
genetic allocation of parentage proofed that in all three cases putative parents and
biological parents were identical. In conclusion, all fawns were the result of the natural
matings in summer with the physiological duration of pregnancy and not the result of the
embryo transfer program in autumn. No statement can be made about the possibility to
influence embryonic diapause or about the dependence of eD on external or internal factors.
It is still not clear who gives the signal for the resumption of embryonic development, mother
or embryo. In spite of induction of a new cycle via luteolysis going along with development of
new corpora lutea and temporary decrease of progesterone concentrations, none of the
pregnancies was terminated and embryos were not resorbed. All females carried their fawns
to term, which leads to the conclusion that in contrast to other animal species in roe deer,
during the diapause, maintenance of pregnancy must be largely independent from the
presence of progesterone. This finding is considered to be another reproductive particularity
of European roe deer. |
