Effects of in-phase and out-of-phase ovulation induction on early mouse embryos

The effects of ovulation induction on pre-implantation embryos (day 4 of gestation) were studied in mature cycling mice (the Jcl:ICR strain) using relatively small doses of pregnant mare's serum (PMS)/human chorionic gonadotropin (HCG) (2.5 or 5 IU each) given at two different stages (in-phase or out-of-phase to the estrous cycle). The proportion of degenerated embryos was increased and the development of the embryos was retarded in the treated groups, especially in the out-of-phase subgroups. Therefore, we propose that the use of PMS/HCG for ovulation induction should be more restricted in mouse reproductive experiments when mature females are used, and that, even when ovulation induction is used, a treatment synchronized to the spontaneous estrous cycle should be elected.