If you’ve been keeping male and female mice in the same cage there is a good chance they will breed.
First or all I have to point out that you shouldn’t be keeping female and male mice together or deliberately breeding mice unless you’re an experienced breeder or prepared.
However, if it’s happened you need to know how to tell if a mouse is pregnant in case you need to do anything to ensure the pups are born safely.
Generally speaking, you should not interfere with the pregnancy unless there are some obvious dangers or issues.
Doing so can actually cause some issues for the expecting mother. In extreme cases, they may even abandon their young, especially if their scent is compromised.
How to Tell If a Mouse Is Pregnant
Looking for the Plug
You’re not going to be able to tell without having a good look.
There is an obvious sign, however. After mating, female mice have what’s called a ‘plug’ in their vagina. This is basically excess semen left by the male and its natures way of preventing other males of mating with the female.
The plug will only stay in place for around 24 – 48 hours. So it’s very likely you will miss it while it’s in the female, you may see it when it’s fallen out and is in their cage.
Another sign that your female mouse is pregnant will be nest building.
Mice tend to start gathering bits and pieces from around their environment and building a nest between 1-2 weeks before giving birth.
Without interfering too much you can make sure they have enough shredded paper, bedding, and a space to build the nest.
By the time the female is two weeks into her pregnancy you will be able to notice she is carrying just by looking at her.
You’ll see the extra size in her tummy, you might notice enlarged nipples, and you may have noticed she is less active.
All you can do for now is keep an eye on her, make sure she has enough food and water at all times, and that there is nothing in the cage that can cause injury.
Pregnant Mouse Behaviour
You will notice some behavioural changes in mice that are pregnant.
Nesting is the most obvious behaviour that they were not doing before. They will start building a nest to prepare for giving birth.
They like to choose a warm and dark spot in their cage for the nest. More often than not mice give birth at night, so you will probably wake one morning to see the offspring have arrived.
Never touch the nest, mother, or young for a few days at the least. This can cause the female to freak out and may be fatal to the pups.
You may also notice the female becoming less active and eating more as a sign she is pregnant.
Mice tend to eat foods a little richer in fats if they’re offered when they are feeding for more than just one. Plus, for obvious reasons, they will not be racing around the cage as much.
Mouse Labour Signs
Mice are pregnant for around 20 days. As the mouse enters into labour you will see some or all of the following signs:
- She is uncomfortable and stretching more than normal
- She is not moving much and looks a little distressed
- She is breathing heavily
- You may see the pups moving through the wall of her tummy
Once you start seeing these signs you can expect the babies to be delivered within 24 hours.
Mouse Pregnancy Length
The length of pregnancy for a mouse is known as the gestational period, and this is between 18 – 22 days.
This number will vary depending on the species but typically isn’t much different.
It’s a fascinating process to be witness to in my opinion. If you have a pregnant mouse enjoy watching the beautiful little pups born, the happy mum, and enjoy seeing one of nature’s wonders.