Although laboratory rodents are used to study estrogen-related disorders, they are different from humans in that they do not menstruate. Therefore, they are not used to understand or develop treatments for disorders related to menstruation, like endometriosis, premenstrual syndrome (PMS) or some fertility disorders.
Researchers from Monash University (Australia), have now reported they've discovered a rodent that actually has a menstrual cycle similar to humans. The spiny mouse (Acomys cahirinus) has about a nine day cycle that includes three days of bleeding (shedding of the endometrium and evidence of blood in the vaginal canal), which is a similar ratio to the human cycle. This was discovered by flushing the vaginas of spiny mice as well as other species that were known not to have menstrual cycles and looking for evidence of blood. They are continuing to examine the uterine structure and changes in gene expression throughout the menstrual cycle to see how similar these are to humans. This is a very interesting finding as reportedly only 1.5% of mammals have a menstrual cycle and as you can imagine, most are primates. In fact, baboons are currently used as a model for endometriosis.