The effects of donors hormonal treatment and embryo developmental stages
on the survival of vitrified rabbit embryos were examined. Thirty six virgin New
Zealand White rabbit does aging 6-7 months were divided in two groups. Does in
the 1st group (n=24) were treated with intramuscular injection of 20 μg GnRH/doe
for induction of ovulation and artificially inseminated. Does in the 2nd group
(n=12) were treated with subcutaneous injection of 80 IU PMSG/doe and 68 h later
with intravenous injection of 50 IU hCG/doe for the induction of superovulation
and artificially inseminated following hCG administration. Eight and four does
from the 1st and 2nd groups respectively were slaughtered in each of 24-26, 48-50
and 72-74 h after insemination for embryo collection. Embryos at various
developmental stages were vitrified. Upon de-vitrification, embryos were evaluated
for viability as indicated by the morphological appearance and subsequent
development in culture medium for 48 h.
The percentage of normal embryos vitrified and embryos post-thawing with
morphologically normal appearance recovered from GnRH treated does were
higher than that obtained from superovulated donors (93.05 vs. 77.43% and 75.86
vs. 67.43%, respectively). Only 63 (36%) of 175 superovulated embryo vitrified was
cleaved in vitro post-vitrification compared to 89 (51.15%) of 174 control embryos.
No significant differences were observed among embryo developmental stages in
the percentage of vitrified normal embryos. The percentages of embryos recovered
post-vitrification with morphologically normal appearance were significantly
(P<0.05) higher in later developmental stages compared to earlier stages. The best
percentage of embryos developed in vitro have been obtained after de-vitrification
at the early blastocyst stage, followed by that at compacted morulae and morulae
stages, whereas the lower percentage were recorded with embryos vitrified at 2-
and 4- cell stages. Markedly high in vitro development rates (84.85-92.31%) were
obtained in morulae, compacted morulae and early blastocyst stages in control
embryos compared to 63.33-81.48% in embryos produced through superovulation.
These results show that treating donor with GnRH achieve the best embryos for
cryopreservation and also rabbit embryos at morulae, compacted morulae and
early blastocyst stages are appear to be proper candidate stages for
cryopreservation.