Cryopreservation is cost and time saving method enabling preservation of valuable transgenic lines that are not currently in use. Freezing of sperm or embryos is always recommended, as they constitute a ‘back-up’ in case of disease outbreak, fertility problems, spontaneous phenotype loss, etc. A complete cycle of cryopreserving a strain and reconstituting it from frozen material involves the same biological steps whether one uses embryos or sperm. In both cases, the production of fertilized embryos is the most expensive step. With embryo cryo, the fertilization step takes place before freezing, whereas with sperm cryo it is done after thawing.

Comparison of mouse sperm and embryo cryopreservation:

 

Sperm

Embryo

Advantage

Cheaper to cryopreserve, requires 1 day of work, requires only 2 males/line

Embryos are frozen post fertilization, easier to recover the offspring

Disadvantage

The only gemetes that are frozen are males, rerival through IVF (costly and labor extensive), must use WT females as egg donors (the offspring always heterozygous)

More animals required, males and young females, requires the hormonal induction of superovulation,

Number of animals needed

Minimum 2 males/line

3-5 males and  i 8-20 young females

Days of experiment

1 day

At least  1-2 weeks,

Cost

2500 PLN/line

4500 PLN /line

Additional cost-recovery

IVF + embryotransfer (6000 PLN)

4000 (embryotransfer)