estrous cycle is a recurring physiologic change in libido, which is induced by reproductive hormones in rodents. This cycle is very short in rodents including mice. It persists for 4 or 5 days. Defining the estrous cycle is important for specifying the exact time of the mating period. It represents the beginning of the pregnancy in mice. Having short time period in estrous cycle makes the rodents in advantage in reproductive studies. Because of the difficulties in uses of this technique in mice, generally rats are preferred. The uses of genetically engineered mice increase in resent medical research studies. So, it makes important the determining of estrus cycle in mice. The main steps of the procedures are the obtaining of vaginal samples for having vaginal smear and the determination of the cell types in vaginal smear under the microscope. There are many different studies about this topic in the literature. Vaginal swap methodologies are favorable for the first step of these procedures. In the determination of the cell types from vaginal smears, some methodologies prefer the analyses of cell types under microscope without any staining. In other methodologies, some chemicals prefer for the staining of the cells obtained from vaginal smears. In our lab, a rapid, simple and effective methodology was established in the determination of estrous cycle in mice. Vaginal washing methodology was applied in first step instead of vaginal swap methodology. In the preparation of mouse vaginal smear, toluidine blue was used for staining. In the evaluation of cell types, light microscope was used. By this methodology, the pregnancy ratios were increased statistically and it is possible to obtain the oocyte and embryo of desired date by knowing the exact time of pregnancy. These findings represented that our modified methodology is more rapid and easier in the application and more effective in the evaluation than other methodologies in defining the estrous cycle in mice.

Keywords: Estrous cycle, mouse, vaginal smear, toluidine blue