06.02.2023: A key technique in biomedical research is the surgical transfer of embryos in mice. A recently published study conducted by researchers at the University of Veterinary Medicine Vienna (Vetmeduni) investigated ways to minimize the negative effects from this procedure. As a result, the researchers make a clear recommendation for the use of unilateral right-sided transfers, as this is the best way to implement the 3R Principle for greater animal welfare while optimizing reproductive outcome.

Surgical embryo transfer in mice (Mus musculus) is a key technique in assisted reproduction that is applied for various purposes in biomedical research including the generation or conservation of mouse models. The procedure requires several steps, such as the preparation of embryo donors and recipient females, embryo culture, and the transfer itself. Considering the enormous number of embryo transfers that are conducted in research laboratories worldwide, each step must be optimized in order to minimize animal suffering in keeping with the 3R Principle: replace – avoid the use of animals in research; reduction – reduce the number of animals needed; and refinement – improve the methods used to reduce the impact on animals.

Significant differences based on type of embryo transfer

In their study, the researchers investigated the effect of bilateral and unilateral left- or right-sided oviduct transfers on embryo transfer success. Surgical embryo transfer is currently the most commonly used transfer technique in mice and can be performed bilaterally or unilaterally into the oviduct or the uterine horn.

“In total, we performed 223 embryo transfers, in which we transferred 10 to 14 two-cell embryos each. We found that the type of transfer significantly influenced both the pregnancy rate of recipients and the survival rate of transferred embryos,” says study first author Kerstin Auer from the Institute of in vivo and in vitro Models at Vetmeduni.

Recommended gold standard: unilateral right-sided transfer

Bilateral transfers yielded higher pregnancy and embryo survival rates than left-sided unilateral transfers. Right-sided unilateral transfers yielded higher pregnancy rates than left-sided unilateral transfers and did not differ in embryo survival rates from bilateral transfers. The number of transferred embryos had an effect on the pregnancy rate; however, the number of born pups increased with the number of transferred embryos. In conclusion, unilateral embryo transfers into the right reproductive tract yield equally high pregnancy and embryo survival rates as bilateral transfers.

The study’s final author, Thomas Rülicke from the Department of Biomedical Sciences at Vetmeduni, therefore makes a clear recommendation with regard to future embryo transfers in mice: “Given that a second abdominal incision can be prevented, and the time of surgery can be reduced, we recommend applying unilateral right-sided transfers, as this would reduce post-operative pain and lower the impact on recipients, while providing equally good results.”
 

The article “Comparison of unilateral and bilateral embryo transfer in mice” by Kerstin E. Auer, Thomas Kolbe, Claudia Laschalt and Thomas Rülicke was published in Laboratory Animals.

Scientifc article