Breeding Mice

Pet mice, or ‘fancy mice’ as they are known, are not difficult to breed once you are aware of the do’s and don’ts. Female mice, or ‘does’ as they are called will likely breed if housed with, or introduced properly to males ‘bucks’. To make sure your mice have litters as comfortably and healthy as possible there is some support you can offer. You will need to have enough cages, healthy mice and understand when to introduce and remove the mating partners.

Why do People Breed Mice?

There are a few different reasons why people choose to breed mice, most often it is to increase their numbers of mice because they enjoy them as pets. Mice make great pets for pet owners of all ages and levels of experience. They enjoy socialising and interacting with people and are happy sitting in the palm of someone’s hand, or running up and down their arms.

Mice rarely ever bite or harm people, if this does happen there is usually a good reason behind it and you were probably warned without realising. Due to mice having a lifespan of around 18 months it is not always easy to find baby mice so some people prefer to breed their own litter.

Optimal Breeding Age and cycles

It is possible for female mice to start having litters as early as four weeks of age. The optimal age however is when the mouse is at least 12 weeks old, this greatly increases the chance of a safe delivery of healthy babies. The oldest age a female should be bred is around 8 months.

A doe should be not be re-introduced to bucks until around a month after giving birth to allow full recovery. Also, does should not have more than 3 litters in a lifetime, exceeding this number of litters can affect their health and lifespan, along with the babies of future litters.

Choosing and Introducing Mates

When choosing the buck to use as the mate you need to make sure of the following; the buck is mature and in good health, not aggressive to other mice, and does not have any signs of genetic problems that may be passed on.

When introducing the buck you need to introduce the female into his cage. This will lessen the likelihood of the doe fighting for her territory and allow them to be introduced peacefully. Sometimes there will be isolated cases of fighting, unless this continues for several minutes or becomes frequent it is nothing to worry about. A female will often have to fight off the male when she is not on heat. If you are concerned that they are fighting too often you will have to put the female back into a separate cage.

Every 5 days or so female mice are on heat. It is recommended you leave the female in the cage with the male for around 10 days before removing and placing her into a separate cage, this will ensure two cycles and usually be enough time for a successful mating.

The gestation period of mice is 21 days on average, with litter size being around 10-12 babies. You should assume that your mouse is pregnant after removing her from the buck and change their diet a little. Adding more fatty/protein foods into their diet will help with a healthy pregnancy. You can use cat or dog treats, or prepare some pieces of cooked meat and egg whites along with the normal mouse food mix.

Make sure that there is always fresh water available and add plenty of bedding to the cage so the female can make a nice big nest.

How to Tell Your Mouse is Pregnant

There are several ways to tell if your mouse is pregnant, if you are unsure you can check the following:

Building nests – A pregnant female will start building a large nest for the expected babies. It will either be in her existing sleeping area or a new area in the cage. Make sure you provide plenty of paper strips for her to use and do not disrupt this area when cleaning the cage.

Larger stomach – This is the obvious one, although some mice with a small litter will not be showing much if at all. It is not unheard of for owners to be surprised when they find a litter of new born pups in the cage all of a sudden, completely unaware they had a pregnant female.

Female is ‘plugged’ – After mating with a buck the female will have a plug preventing any further mating for 2-3 days. This is formed by excess fluids from the successful mate, it does not guarantee a successful pregnancy however.

Changes in behaviour – A pregnant mouse will behave differently than it did before mating. There will be times that she is very tired and lethargic. Or she might become anti-social and a little short tempered.

During and After Birth Instructions

You will not need to do anything during birth and it is recommended you do not touch either the mother or her young for at least the first two days. After four days have passed you can handle the young, this will help tame them for future handling. If you want to know the sex of the new born mice, the females will have visible nipples and the males will not.

At around two weeks old they will open their eyes fully and start to become active. If you have not handled young mice before you will need to be very cautious as they can make very quick movements with little warning. Being curious like all young animals they can do themselves an injury by jumping out of your hands, or falling off somewhere you have placed them.

At around five weeks old you can separate the male and female mice into new cages to avoid any more breeding. They no longer require their mother to look after them and can be rehomed if necessary.