Observation of estrous cycle in sexual maturation and ovariectomized female ICR mice

AIM: To observe the characteristics of estrous cycle of female ICR mice and ovariectomized mice that had reached sexual maturity stage. METHODS: ICR mice were randomly divided into 3 groups, normal group, sham operation group and ovariectomized group. After ovariectomy and sham operating, at the 8th day, the mice were taken vaginal smears twice daily (09:00 and 16:00) for 12 consecutive days. The feature of vulva in the mice and vaginal smear cytology, occurrence rate of regular estrous cycle, duration of estrous cycle and each stage duration of estrous cycle were recorded and observed. RESULTS: The characteristics of estrous cycle in normal group and sham operation group were similar. Nearly 85% of the ICR mice in sexual maturity stage showed regular estrous cycle. The majority manifested 6-day cycle (83%), and only a small number exhibited 5-day cycle (17%). Compared with 5-day group, the duration of oestrus was significantly increased in 6-day group (P<0.05). The number and kind of the cells in vaginal smear were a little different between 5-day and 6-day groups. The ovariectomized mice which showed irregular estrous cycle (76%) were characterized by continuous diestrus. CONCLUSION: Female ICR mice have the strain characteristics of estrus cycle.