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.
Female mice are only receptive to male mice while they are in estrus.
Mating generally occurs within 24 hours of introducing a male and an 'in estrus' female mouse, though the female is most receptive during the first few hours. There may be frequent, short copulations before adequate intromission and ejaculation occur. Mice copulate by having the male mount the female from behind while she is in a normal standing position. The secretions of the accessory sex glands in the male will form a waxy congealed plug in the vagina of the female. This plug may fall out after 24 hours.