One of the most prolific members of the rodent family, a pet mouse can reproduce quickly, breeding as often as every 20 days. With an average lifespan of 18 months, and an average of 10 babies per litter, a single female mouse can produce more than 300 offspring in her lifetime, making careful sexing a necessity unless you wish to become a mouse breeder. While pet mice are entertaining, fun and inexpensive pets, they do require constant maintenance, cleaning and care, so use caution in housing the same gender together.
A mouse reaches breeding maturity between three and four weeks of age. It can be very difficult to differentiate between mouse genders, and many pet stores that sell pet mice often house members of the same sex together. This means if you buy a mouse from a pet store, it may very well be pregnant. Mice have a gestation period of 17 to 20 days and can have litters ranging in size from 1 to 20 pups. Those pups then reach reading breeding maturity quickly and, unless segregated into gender-specific housing, can quickly reproduce.
Caring for a Pregnant Mouse
An expectant mouse mother requires an adequate supply of food and water and thrives best in a quiet, low-stress environment. Once pups are born, it is advisable initially to avoid disturbing the nest, even for cleaning. Do not touch the new pups if possible, as the unfamiliar scent can be confusing to the mother. If you must handle mice pups, dust your hands with bedding to cover up your natural odor. Once the babies open their eyes, usually in four to six days, you may gently clean portions of the cage around the nest and replace bedding. Pups will be weaned from their mother at three to four weeks and will be of breeding age soon after.
If you have a mouse litter, and don't wish to induce a population explosion, separate young mice by gender as soon as they're weaned. Sexing can be tricky. Mice have two opening on their underside, and in the female, the openings are close together, and in the male, they are further apart. If you can’t tell the gender of your mice, have a professional sex them for you.
Many mice owners intentionally breed their mice and sell the babies to pet stores or laboratories for a profit. While this can be a good way to earn extra cash while raising pet mice, consider the fact that many pet stores resell mice not as pets, but as snake and reptile feeders, and labs use their mice for testing purposes. If this isn't something you are comfortable with, limit the litters of pups your pet mice produce or find individual homes for the offspring.
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