Project Summary The goal of this project is to establish large-scale oocyte cryopreserve and assess the viability, cost and animal savings, as well as determine what factors may influence the recovery of viable rederived mice. Our experience in cryopreservation has shown varying quality of recovered oocytes among different vendors, even within a specific mouse strain. We will cryopreserve oocytes from C57BL/6N mice from the four most commonly used vendors (Jackson, Charles River, Taconic and Envigo). We compare the quality of oocytes through IVF to the blastocyst stage as well as to live birth. We will also examine possible corollaries to embryo quality including genome aneuploidy and the microbiome of the donor dams. This data will inform our implementation of large-scale preservation and rederivation and identify factors that influence successful outcomes. This proposal will lead to efficiencies in cryopreservation of haploid gametes (oocytes) and success would; i) reduce costs related animal shipments required on demand of a project ii) would eliminate the requirement to synchronize oocyte production and ET recipient mice’s estrus cycle, iii) enable testing of each batch of oocytes for developmental competency, iv) improve successful live pup production rates and reduce the time between when a researcher orders an IVF recovery and we can provide animals, v) and collectively, the use of cryopreserved oocytes will reduce the operating expenses of MMRRC. This information will be shared with the other three MMRRCs either during our monthly consortium meetings or during our annual consortium meeting. Additionally, this information will be shared widely through publications and presentations.