The female is polyestrus, with the estrus lasting 4-5 days. The length of estrus can vary considerably depending on a number of factors. Males are able to breed at any time after puberty. Estrus can be detected by performing a vaginal swab or lavage and examining cells microscopically. There is an increasing population of cornified squamous epithelial cells with pyknotic nuclei, as the animal approaches estrus.
Leukocytes gradually infiltrate during diestrus.
Anestrous is characterized by non-cornified epithelial cells. Red blood cells are not prominent during proestrus as in the canine. Estrus can be induced in mice with progesterone and estrogen or PMSG and HCG, though it is more practical to just wait another 4-5 days for the next estrus. Estrus can be supressed by the presence of other females or the presence of a strange male. Estrus can be stimulated by introduction of a male.