Used in embryo freezing
The Jackson Laboratory's Reproductive Services group routinely superovulates large numbers of female mice. Through the administration of gonadotropins, female mice can be induced to ovulate a greater number of eggs than normal at a predictable time. The superovulation technique described below has been used in the collection and freezing for storage of literally millions of embryos from hundreds of strains of mice for both our in-house research faculty and offsite customers.
Response to gonadotropin injection varies from strain to strain. Optimum dose and age of the mice is determined for each strain by doing preliminary dose response injections. Generally, doses of 2.0 to 5.0 international units (IU) per mouse of each gonadotropin and ages of 21-35 days (body weights of 12-14 grams) will give the best yield of fertilized eggs.
Female mice are injected interperitoneally (IP) with pregnant mare serum (PMS) between 1:00 and 4:00 PM of Day 1. The females are housed five or fewer per cage.
On Day 3, forty-two to fifty hours after the PMS injection, the mice receive an IP injection of human chorionic gonadotropin (HCG). Immediately following injection, a female is mated with the appropriate stud male. Males, 8 weeks of age or older, are housed individually and the female is always placed into his cage.
Ovulation occurs approximately 12 hours after the HCG injection, at which time the eggs can be fertilized.
Checking for vaginal plugs
In the Embryo Freezing Laboratory, checking for vaginal plugs is not generally performed on the day after HCG injection and mating. Experience has shown that females often will become pregnant when no plug has been observed.