Genetically modified embryos must be transferred to a suitable female recipient for development to pups. Nonsurgical embryo transfer is a fast and efficient method used to deliver blastocyst stage embryos to the uterine horn of recipient females. The efficiency of recovery of pups after nonsurgical embryo transfer is similar to the efficiency after surgical transfer. However, nonsurgical transfer eliminates the pain and distress caused by the surgical procedure and provides a refinement in accordance with Russel and Burch's "3Rs" (The principles of humane experimental technique. Methuen & Co., London, 1959), an ethical framework for animal research. This method is also useful for rederivation of mouse strains. Rederivation is important for either removal of potential pathogens from an incoming mouse strain after shipping, or within a facility to obtain a clean mouse colony.
Keywords: 3Rs; Anesthesia; Animal welfare; Embryo; Embryo transfer; NSET; Nonsurgical; Rederivation; Transgenic.