Naturally sterile hybrid mice for the production of embryo transfer recipients

To produce and distribute genetically modified (GM) mouse models, pseudopregnant embryo transfer recipients are required. For their preparation, vasectomized mice are commonly used, generated by surgical procedures associated with pain and discomfort. Sterile GM strains provide a non-surgical replacement. However, maintenance of GM strains requires extensive breeding and genotyping, which are regulated procedures and their breeding leads to a large wastage of animals, as mice of incorrect genotype are discarded.  In contrast, certain wild-type hybrid males, generated by the simple intercrossing of two different wild-type strains, are sterile. We have been exploring the use of these sterile hybrids as alternatives for producing pseudopregnant embryo transfer recipients and find their behaviour to be indistinguishable from those generated by vasectomized males.

The method provides two substantial 3R impacts
- refinement, when comparing the use of these naturally sterile hybrids with vasectomized males, as clearly no surgical procedures are necessary
- reduction, when comparing the use of these naturally sterile hybrids with sterile GM mice, as the breeding is substantially more efficient, with all males born from production crosses being suitable for use.

The value of a 3Rs initiative is only as good as the uptake in the community. We thus plan to select a naturally sterile hybrid, which can be generated from strains which are common and easily sourced: the F1 hybrid between Mus spretus and C57BL/6 is a good candidate and we have confirmed the sterility of this strain and its good husbandry characteristics.

We seek funding from the NC3Rs to validate the use of this hybrid as a replacement for surgical vasectomized or sterile GM males. Importantly, we plan to achieve this comparison within three different research environments and thus validate its dissemination to achieve a maximal 3Rs impact.

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Skills and Knowledge Transfer grant



Principal investigator

Dr Benjamin Davies


University of Oxford


Dr Martin Fray
Dr Antony Adamson

Grant reference number


Award date:

Sep 2020 - Feb 2022

Grant amount