Anti‐fertility effect of levonorgestrel and/or quinestrol on striped field mouse ( Apodemus agrarius ): evidence from both laboratory and field experiments

The effect of combined levonorgestrel (P) and quinestrol (E) on the fertility of striped field mouse (Apodemus agrarius) has not been evaluated. We performed a series of experiments in both the laboratory and field to assess the effect of P and/or E on the fertility of A. agrarius. In the laboratory, to test the time-dependent anti-fertility effects of P and E, as well as their mixtures, 90 male striped field mice were randomly assigned to 6 treatment groups (n = 60), and a control group (n = 30). Mice in 3 treatment groups were administered 1 of the 3 compounds (1 mg⋅kg-1 [body weight] EP-1, 0.34 mg⋅kg-1 E, 0.66 mg⋅kg-1 P) for 3 successive days (another half for 7 successive days) via oral gavage; mice were then sacrificed 15 and 45 days after initiating the gavage treatment. Our findings indicated that E and EP-1 treatment, but not P or control treatment, significantly decreased the sperm count in the caudal epididymis, as well as the weight of the testes, epididymides, and seminal vesicles. Additionally, fertile female mice mated with E- and EP-1-treated males produced smaller pups. These data indicate that E and EP-1 can induce infertility in male A. agrarius. In the field, the population density of A. agrarius was significantly influenced by EP-1, and the rodent density in the treatment group was lower than that in the control group. Overall, our results indicate that EP-1 is an effective contraceptive in A. agrarius, a dominant rodent species in the farmland.