House Mouse General Facts

By | April 28, 2018

The Fun Mouse: Mouse Information: House Mouse general facts.


Housing Temperatures

Mice should be kept between 65*F and 80*F at all times. Temperatures exceeding this can cause chills, lethargic mice, illness, and even death.


The humidity level should stay between 30% and 70%. Too high humidity can cause ringtail, higher ammonia levels, and illness while lower humidity can cause dryness of the skin.

Health Physiology & Anatomy

*Based on a 20g mouse.
*Data will vary based on age, size, weight, weight, individual, strain, environmental conditions, etc.

Blood pressure

83-164 mm Hg (millimeters of mercury)

Heart rate

A healthy new born should have 286 +/- 56.8 bpm (beats per minute) and an adult should have 632 +/- 51.3 bpm.

Respiratory rate

~163 per minute

Body temperature



Mice have 16 teeth. Unlike humans, mice do not loose baby teeth and grow adult teeth. Mice have one set of teeth their entire life. However, they continue to grow throughout life. The top front teeth of the mouse (incisors) should slightly overlap, in front of, the bottom teeth. If the bottom incisors are in front of the top, this is called malocclusion. If the teeth butt up against each other, this is called simple malocclusion. Malocclusion can cause the teeth to break, wear oddly, cause severe damage to the mouth, and make a mouse unable to eat. It helps to give them something to chew on, but this will not likely fix the problem (because their teeth grow their entire lives, mice should have something to chew on always, malocclusion or not). It is likely that a mouse with malocclusion will need vet attention, to trim the teeth down. Never attempt this on your own, as teeth can easily be pulled out accidentally. This can possibly resulting in death of the mouse because he/she can’t eat.

Life cycle


Mus musculus

Life span

1-1/2 to 3 years. 2 years being the average. (wild mice live longer.. around 5 years in captivity, though only around 6 months in the wild due to predators and environmental factors).


4 – 8 weeks of age, varying from line to line and mouse to mouse. This is the time that males and females can become fertile. However, note that a female can die if she conceives that young. **see below.

Females estrus (heat) cycle

Every 4 to 5 days all year round until becoming pregnant. *Sometimes estrus will stop in all female colonies and pick up again roughly 3 days after a male is introduced (this is called the Whitten Effect). Sometimes females will also have odd cycles in the winter.


Some sources (from Labs) claim 2-3 hours, some claim 12 hours.

Complete Physical Maturity

Mice are not done growing until they are between 3 and 5 months of age, depending on the line. Mice should NEVER be bred until they are at least 12 weeks age. If you don’t know the line really well, wait until at least 12 weeks, if not longer. Some mice are not fully developed until 5 months of age! Breeding too young can cause a weak mother, weak babies, shorter life spans, and even death of all of them!

Optimal Breeding Age

Unless the line is extremely well known, the best breeding age for a female mouse is between the ages of 3 months (though it’s best to wait until 4 months) and 8 months. Fist litters should be done before the mouse is 6-7 months of age. These time frames can vary from line to line, but this is a general rule for safe breeding. It is of no health risk to the male or his offspring to breed him at any age as long as he is healthy. Keep in mind however, that a male might be fully fertile at 4 weeks or as late as 8 weeks.


19-24 days. The average is 20 days.

Postpartum Estrus

A female can come back into heat 14-28 hours after giving birth! This means that she can become pregnant after having her litter! Females should NEVER have back to back litters. It risks the health of the mother as well as the babies. It can even result in death of some or all of them (including the mother)!

Litter size

1-24 pups. The average is between 9 and 12 pups. A first time mom often has fewer pups.

Ears open

Ears can open as early as day 3, but some don’t open until days later.

Eyes open

Babies open their eyes around day 14, give or take a few days depending on the litter.


4 weeks of age. It is best not to take the babies from their mother until they are 4 weeks of age, to the day. Once the males are 4 weeks of age, they need to be taken away from the group to prevent unwanted breeding (to the mom and the sisters). Also note that males often need to be separated from each other at that time. Male mice, especially those from pet shop mice and lines that haven’t been *thoroughly* tracked, will fight to the death. Even siblings will fight 99% of the time. Fighting usually happens without ANY notice what so ever and at night, when their caregiver(s) are not around to separate them. Fighting to the death is quick and usually completely unpredictable/unpreventable without separating them all at 4 weeks.

End of Fertility

Most mice are fertile any time after 4 weeks of age until death. NEVER assume that either sex is too old to produce offspring. As a mouse ages, it might take them longer to actually produce a litter (due to lower sperm count or irregular estrus cycles) or conception could happen in a matter of less than a second. Pregnancy in females can and will occur late in life, if given the chance, though it can be detrimental to the mother as well as the offspring (often resulting in death).


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