Rederivation is used to eliminate pathogens from mice to establish clean, healthy breeding colonies . Rederivation can be performed by using either IVF techniques or standard rederivation practices.
This is the fastest and least expensive option as well as the one likely to yield the most clean pups. IVF is performed by transferring washed embryos into disease-free recipient females. It will require the sacrifice of one sexually mature male (10 weeks or older) which will have its sperm collected and frozen (it is recommended that at least two males are actually imported). The line can then be reanimated using female oocyte donors from a standard inbred strain. This currently only includes C57BL/6J, and FVB/NJ. Mice from smaller colonies may be available with sufficient notice. Time from arrival to release is less than 6 months.
Standard rederivation is generally much slower and yields fewer pups than IVF. This option is used for lines that are sex-linked or when it is preferable not to mate mice onto the background strain. This may be because the background strain of the imported line is not held at ABR, the imported line is on a mixed background, or the line is homozygous for multiple genetic modifications. Standard rederivation will require 3 breeding pairs, 4-5 male studs and approximately 10 females at 4 weeks of age. Due to the extra breeding requirements, this option can take 6- 12 months to complete.
After rederivation, the recipient females and the rederived progeny undergo health screening to ensure that all pathogens have been removed. Samples for this health screening are taken after the progeny mice reach 10 weeks of age, with results taking at least another week to receive. Mice are typically expected to be released by 12 weeks of age.