I want to breed my mice, what do I need to know?

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Before you do anything, here’s a few things to think about:

  • What will you do with all the babies? Mice often have litters of 12 or 15, and can have 20 or more in some cases – can you keep them all, even the boys? Taking ‘surplus’ babies to a pet shop is far from ideal, as they may simply end up as someone’s dinner :(
  • What will you do if your pregnant mouse has a problem during delivery and needs vet attention? It’s a good idea to have both a trustworthy vet with small animal experience, and the necessary money on hand, should something happen.
  • Do you know the backgrounds of the mice you want to breed? Breeding pet shop mice which are likely riddled with cancer, immune deficiencies or temperament issues is a bad idea. Make sure you know that the mice you choose are from long-lived, healthy and well-tempered lines with pedigrees that go back at least 3 generations so you don’t get any nasty surprises. Knowing their genetic history will also help you plan for what colours and markings your babies will likely be.

If you’re still sure you want to breed your mice:

  • Female mice become fertile at approximately 5 weeks old, but that does NOT mean it’s a good idea to start breeding them at that tender age. The best age to breed a female is between 4 and 6 months old. Make sure she is fully mature and at her adult size before breeding her, or it could negatively affect her and her babies’ health and development. Any older than about 9 months is a risk, as older females that have not had a litter before often have fused hips that will make delivery dangerous or impossible.
  • You need a male and a female, obviously. If you only have a female, many breeders will be willing to stud out a male. This way, you can ask about his history before deciding. You’ll find less people interested in lending a female to breed with if you only have a male, so you may be better off buying a pedigreed female instead.
  • Always put the new couple into a clean cage. Females especially can be quite aggressive and territorial towards an interested male, and even if in a different cage, can often be forcefully protestant for the first few days. You’ll probably see him going after her a lot and her squeaking like crazy and running away. He probably won’t hurt her, but it can be a stressful time – for the mice, and for you!