How Long Are Pet Mice Pregnant? Gestation Period & Reproduction

Mice are found throughout the world and are common and popular pets. They only need a relatively small amount of space to live, they can be handled if they are used to being picked up, and they are cute and fun to watch, although their nocturnal habits and their tiny size mean that they might not be the best pet for very young children.

However, one area of concern for some owners is their propensity to breed. A female mouse can have as many as 50 pups in a single year, so owners need to take care to ensure that they aren’t quickly overrun by little mice feet. Whether planned or accidental, your mouse will be pregnant for about 20 days and will typically have a litter of between 10 and 12 pups.

The pups need to be left alone for the first 7 days and by the 2-week stage they will look like small adult mice rather than little pinkies. Read on for more information about the gestation period and reproductive cycle of mice, as well as some signs that your female mouse might be pregnant.

Mouse Reproductive Cycle

Mice reach sexual maturity at just 6 to 8 weeks, and one of the most common reasons for unwanted litters is that owners didn’t separate young male and female mice in time. Always err on the side of caution if you are looking to avoid your female mouse getting pregnant. Another common cause of unwanted litters is that female mice can get pregnant virtually straight away after giving birth and certainly while still nursing one litter. This means that the male should be removed before the female gives birth.

Females go into heat roughly every month and remain in heat for around 4 to 5 days, which means that the female can get pregnant at any point during this time.

A litter of pups can consist of between 9 and 12 pups, and a female could become pregnant every month for a year. Considering some litters will be smaller than others, and there is likely to be a gap between some of the pregnancies, this means that a single female mouse could have 60 mice in a year. That’s a lot of mice to care for, rehome, and separate.

Breeding Mice

Breeding mice is easy. Put a male and female together long enough and the female will likely get pregnant. In fact, if you do keep males and females together, it will be a lot harder to prevent pregnancy than to encourage it.

Before you breed mice, though, ensure that it is the right thing to do in your circumstances. In less than a month, you could have a dozen new mice to care for. This means finding homes or providing homes yourself. There is very little if any profit in breeding mice, so it shouldn’t be done as a profitable venture. And unless you have people waiting to take the babies, you may find it difficult to rehome them.

The 5 Signs That Your Mouse Is Pregnant

If a male and female mouse have spent any time together, there is a chance that the female will get pregnant. Look out for the following signs that your mouse is pregnant.

1. Semen Plug

After mating, a small amount of semen is left at the female mouse’s vagina entrance. This hardens and acts as a plug to prevent further mating. The plug can be visible for between 24 and 48 hours and after this time, it may still be found on the floor of the mouse’s cage. This isn’t a definite sign that your mouse is pregnant, but it is a sign that mating has taken place.

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2. Nest Building

A pregnant female mouse will look to build a suitable nest for the impending arrival of her litter. If you notice that your mouse is hoarding bedding and other nesting items and moving them to a dark, secluded corner of her cage, this could be a sign that she is indeed pregnant.

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3. Swollen Abdomen

A swollen abdomen is a common sign of pregnancy, but it may not always be noticeable in pregnant mice, especially if yours is carrying a small litter. If it is a large litter, however, the belly can appear very enlarged.

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4. Prominent Nipples

The nipples will darken and may become enlarged, which means that they will be more visible than usual.

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5. Behavior Changes

Hormonal changes cause your mouse to undergo some behavioral changes. She may ignore or actively discourage a male in the cage from getting too close, and she may not enjoy being picked up like she once did.

Conclusion

Mice may be small, but they can produce large numbers of young over a lifetime. A single litter of mice pups typically consists of about 10 young, and as soon as the pups are born, the female can, in some cases, get pregnant straight away. Gestation lasts about 20 days with young mice reaching sexual maturity as young as 6 weeks old.

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Featured Image Credit: colin robert varndell, Shutterstock

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