Superovulation Strategies for 6 Commonly Used Mouse Strains

We examined different weight ranges and hormone dosages to determine superovulation protocols for 6 mouse strains commonly used in genetic engineering: C57BL/6NHsd, B6(Cg)-Tyr(c-2J)/J, B6D2F1/Hsd, FVB/NHsd, BALB/cAnNCr, and Crl:CD1(ICR). Mice from each strain were divided into groups based on weight roughly corresponding to those of 3-, 4-, 5-, and 6-wk-old mice. Mice were treated with 5 IU pregnant mare serum gonadotropin (PMSG) and 5 IU human chorionic gonadotropin (HCG). The weights of mice that produced maximal numbers of oocytes in response to these doses were 14.2 g or less for C57BL/6NHsd, 13.7 g or less for B6(Cg)-Tyr(c-2J)/J, 6.0 to 9.9 g for B6D2F1/Hsd, 14.5 to 16.4 g for FVB/NHsd, 14.8 g or less for BALB/cAnNCr, and 23.5 g or more for Crl:CD1(ICR). We then compared PMSG dosages of 5 and 2.5 IU per mouse and determined whether 2 doses of PMSG (5 or 2.5 IU, depending on prior results) administered 1 wk apart, followed by the standard HCG injection, would produce more oocytes when compared to a single dose of PMSG. FVB, B6D2F1, BALB/c, and CD1 mice responded best to a single dose of 5 IU of each hormone, whereas B6(Cg)-Tyr(c-2J)/J mice produced more oocytes after 2.5 IU PMSG. Although C57BL/6 mice given the standard dose produced good numbers of oocytes, the number was higher after 2 doses of PMSG at 5 IU per dose. We conclude that response to superovulation can be optimized based on mouse strain, weight, and the dose and timing of hormone injection.