A new direct transfer protocol for cryopreserved IVF embryos

The global demand for in vitro-produced (IVP) embryos of determined sex has greatly increased over the last decade. Efficient protocols for the direct transfer of IVP embryos are lacking. This study aimed to compare the pregnancy rates for fresh, vitrified, or frozen/directly transferred IVP dairy cow embryos. Oocytes (n = 3171) recovered by ovum pickup (n = 112) from Girolando (Holstein-Gir) females (n = 36) were selected and submitted to IVM for 24 hours at 38.5 °C with 5% CO2 in air with saturated humidity. In vitro fertilization was performed with the thawed, sexed semen from 5 Holstein bulls. After IVF, presumptive zygotes were denuded and cultured for 7 days under the same IVM and IVF conditions of temperature and humidity, except with 5% CO2 and 5% O2. Grade I blastocysts were randomly assigned for either the transferred fresh, vitrified/thawing, or frozen/directly embryo transfer into previously synchronized recipient females. Conception rates were analyzed by binomial logistic regression, and a probability level of P < 0.05 was considered significant. The conception rates were 51.35 ± 1.87% (133/259) for the fresh embryos, 35.89 ± 3.87% (84/234) for the vitrified embryos, and 40.19 ± 4.65% (125/311) for the frozen directly transferred embryos. These data demonstrate that IVP embryos with sexed semen could be directly transferred into recipient cows with similar conception rates to vitrified embryos. The comparison found that the use of frozen embryos in direct transfer provides easier logistics and a more practical approach for the transfer of IVP embryos on dairy farms.