Breeding Mice - The Methods


Creating and Maintaining Your Own Strain

Creating an own strain is almost impossible without moderate inbreeding. The rarer the coat-, colour- or marked variety you'll breed is, the closer an inbreeding you will have to use. There are also some dangers in this, and you should prepare yourself beforehand.

Classic Method

In Britain a rodent breeder usually starts with four animals; one buck and three does. This is why it can be very hard to make a British breeder to understand that you want to buy only one buck or doe. All three does are mated with the same buck. Of these litters, keep one buck of one litter and mate the does of the other litters with him. Of these litters, again keep one buck of one litter and does from other litters, mating the does with the buck, etc.

With this method you can quickly get good results, especially if the founding animals have been of high quality. If there have been latent or visible faults in the founding parents, they usually will emerge very strongly in the young after a couple of generations. At this point the breeder gets distressed and usually tries to use unconsidered outcross ruining the forming strain thoroughly. Instead, the breeder should start very harsh culling, that is no to use mice with unwanted qualities for further breeding.

If you use classic breeding method you should pay great attention to the founding stock. If these animals are mediocre, their offspring will be mediocre. All animals should have the desired qualities, i.e., good colour, type and size. There should also be as few as possible faults, i.e., the animals should be as healthy and good tempered as possible. It would be wisest to obtain the founding stock from different breeders in order to have a wider original gene pool. Thus you will be able to get greater variable in the offspring; so by choosing the best mice for future breeding also the best genes will be chosen.

Using Several Founding Bucks

In the method of several founding bucks the breeder uses two, sometimes even more bucks instead of just one. There can be three does, but preferably more. You should choose the bucks using the following method: both bucks should have as many as possible of the desired qualities and neither should lack the same quality. The same goes for the females too. You should have the desired quality present always in one of the founding animals.

While using this method, you should also pay close attention to hereditary faults and illnesses, especially as they emerge more slowly than in the classic method.

Rare Colors, Markings and Coat Varieties

Rare colour can be described as having only a few existing mice. Usually these colors are imported from abroad as new colour- or marked varieties or they are unpopular for some reason (= they haven't done well in shows for a while). The genetic make-up of these colors and markings are usually well known, as well as if it's lethal or not. However, it takes a lot of effort and time to breed these rare varieties. The show success isn't often very good.

You should obtain 2-4 mice at first, preferably does than bucks and check them critically. Most prominent faults are usually small size and poor type but there can also be troubles with the main colour. The strain needs new blood as it can be already very inbred. It pays to use a top-quality buck or to obtain a few bucks that go with the variety you are working on with. These bucks should be very good in quality and they should not have the same faults as the rarer specimens.

The rare-coloured females are mated with these bucks. If the desired colour is dominant, all of the litter will usually be of this colour. If the desired colour is recessive, are the young carriers of this colour. The young are then mated together, but not siblings and preferably not even half-siblings. At this point there should be mice of the desired colour. Of these mice the best are mated together and so forth, so the desired type and size will be slowly stabilized in the strain.

New Colors and Markings Born as Mutations

Sometimes a strange coloured baby crops up in a litter. Before you start breeding more of these "excitingly" coloured mice, you should make yourself clear if this colour or marking is worth the trouble. New colour or marking should differ considerably from the varieties already existing. You should look for a similar colour or marking (or coat variety) in another species; if there is one standardized, you can start stabilizing a colour in your strain.

As there is usually only one specimen of the new variety, you should mate it with one of the parents or its sibling who can be the carriers of the same feature. If the new feature is dominant, the whole litter has the desired quality. If it is recessive, will the whole litter carry this quality even though it will not show. When these mice are mated with the parent having the desired feature, should some of the young be as desired. These mice are then mated together to get enough founding stock. In the first stage you have to mate together only close relatives to get more mice with the desired feature. You usually have to give in with type and size too.

Only after you have stabilized the desired feature and you know a little more about it (i.e., is it dominant or recessive, is the gene lethal and is the colour caused by several genes), you can start breeding in size and type using similar methods as with other rare varieties.


Even though you attempt to mate only good animals together, so that the young should also be good, there may be misfortunes. The young may have hereditary faults or illnesses. You may not use these mice for future breeding. Be careful with where these mice end up. You should not sell them to pet shops, as someone may buy them and use them for breeding when these mice can pass down their faults. It's better to try and find new homes for these mice yourself, as long as you remember to tell the new owner that they should not be used for breeding. In the worst case, if the mice have faults that make their living difficult, it is far better to euthanize them.

Text by Minna Koivu.
English translation by Satu Karhumaa.