1st, once the cryopreserved gametes or embryos are frozen and maintained under liquid nitrogen, they can theoretically be held indefinitely without any adverse effects. The first groups of mouse embryos were frozen in 1972 and thawed 25 years later in 1997 to produce live pups in The Jackson Lab.
2nd, the gametes or embryos stored in liquid nitrogen offer a safe way to preserve lines which are potentially but not currently useful, saving space and the expense associated with keeping a breeding colony.
3rd, during the process of gamete and embryo collection most pathogenic organisms are excluded, similar to other methods used to rederive lines of mice.
Once you have identified a strain for cryopreservation, you should test a group of 6 to 10 young (2 to 6 months) homozygous males to determine their fertility. Using experienced males who have already impregnated females gets the project off to a quick start and is less costly than paying us to determine that we can't get fertilized eggs from their matings.
In order for us to be able to use your males, they will have to be transferred to our protocol, but the per diem will be charged to your account. GTTF staff have transfer forms with our information already filled in for you to use. We normally purchase on your account stock females of an appropriate strain to present to your males, resulting in heterozygous embryos for freezing. If your strain requires that we use your females, you should be able to provide 3 week-olds, one per male, for several sessions. We will superovulate the females and present one female to each male once a week, then harvest embryos at the morula stage for the freezing procedure until the requested number of embryos has been preserved
When we have frozen the requested number of embryos, we will thaw one straw to check for viability and we will either return the males to you or euthanize them.