88 PREGNANCY RATES FOR IN VITRO AND IN VIVO PRODUCED OVINE EMBRYOS VITRIFIED USING THE MINIMUM VOLUME COOLING CRYOTOP METHOD
J. Kelly A , D. Kleemann A , M. Kuwayama B and S. Walker AA South Australian Research and Development Institute, Adelaide, Australia
B Kato Ladies' Clinic, Tokyo, Japan. Email: kelly.jen@saugov.sa.gov.au
Reproduction, Fertility and Development 17(2) 194-194 https://doi.org/10.1071/RDv17n2Ab88
Submitted: 1 August 2004 Accepted: 1 October 2004 Published: 1 January 2005
Abstract
Previously we reported that, using the minimum volume cooling (MVC) cryotop vitrification method, in vitro-produced ovine and bovine embryo survival after thawing was similiar to that of fresh embryos (Kelly et al. 2004 Reprod. Fert. Dev. 16, 172). While survival of vitrified embryos after thawing can be indicative of embryo viability, this assessment does not always correlate with embryo survival after transfer. This study assesses the effect of vitrification using the MVC cryotop method on the survival after transfer of in vitro- and in vivo-produced ovine embryos. Fresh or vitrified Day 6 ovine embryos (expanded blastocysts, blastocysts, compact morulae) were used in this study. Ovine cumulus–oocyte complexes were obtained and matured, fertilized (Day 0), and cultured in vitro (Walker et al. 1996 Biol. Reprod. 55, 703–708). In vitro embryos for vitrification were produced and vitrified (Kelly et al. 2004 Reprod. Fert. Dev. 16, 172) 10 days prior to the day of transfer. In vivo embryos were recovered from donor Merino ewes and vitrified 7 days prior to the day of transfer while fresh in vivo embryos were collected and transferred on the same day. Semen used for both in vivo and in vitro embryo production was from the same sire. On the day of transfer, vitrified embryos were thawed directly into 1.25 M sucrose solution, followed by stepwise dilution of the cryoprotectants. Embryos were transferred as singles into synchronized recipient ewes on a randomized basis. Fetal number was detected at Day 50. Variables were assessed using the CATMOD procedure in SAS. Pregnancy rate for in vivo-derived embryos was higher (P < 0.01) than for in vitro-derived embryos. Embryo treatment (fresh vs. vitrified) did not significantly affect pregnancy rate. Pregnancy rate for ewes detected (by vasectomized rams) in estrus within 48 h of progesterone pessary removal was higher (P < 0.05) than for both the 48–68 h and unmarked groups. The latter two groups did not differ significantly. None of the first-order interactions were significant (P > 0.05). This study demonstrates that ovine embryos (in vitro and in vivo) can be vitrified, thawed, and transferred without compromising embryo viability. However, the differences in pregnancy rate between the recipient groups warrant further investigation. The MVC cryotop method is a vitrification technique that can be adapted to routine field use.
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