Mice are easy, enjoyable pets.
They’re small and can be kept in relatively unobtrusive cages. A single male needs 60cm, and 2-3 females will happily live in a cage that size if space is used widely. They’re wonderful to watch, as they’re so active & agile, and easy to handle. They also rarely bite.
Because they’re easy to breed and seen as disposable (cheap) pets people get into breeding mice, having done no research and not understanding the true responsibility that comes with breeding.
So, as someone who has bred well over 30 litters of mice, here are some things to consider.
Let’s say you have one litter of mice, you leave ten babies with mum, and five of them are male. From just one litter, you need seven cages – one for the females, one for dad, and one each for the male offspring.
That’s seven cages of AT LEAST 50cm (80cm+ for six females), and they’re all gonna need cleaning out on an at least weekly basis. Do you have the space, time and money?
Not just for the mice, or the food…but the toys, cages, and vet care! I know someone who just spent over a hundred pounds on her mice that got a URI!!
Cage cleaning takes anywhere from 10-60 minutes depending on the style of cage, size, and how many total you have to clean.
Then there’s the time you must put into handling your mice. For adult pet mice this is easy, you can let them climb all over you for half an hour a day…but add numerous babies/litters into the equation and it becomes quite the time sink! Especially at hopper stage, where more handling helps the bouncy babies settle.
At the hopper stage mice are extremely fast and can be very, very hard to handle. They leap all over the place (hence why many call this the popcorn stage!) with no regard to height or where they’re jumping, and sprint full speed…it’s very easy to lose them at this age!
Rehoming mice is not as easy as many people expect; they’re not a common pet. And, if people do want mice in your area, it’s still extremely hard to pace males – most people want females, who can live together and smell less than males.
And remember, it’s the males who’ll be needing individual cages whilst with you too!
To the untrained eye sexing mice can be difficult way past the point where males are able to impregnate females (from 4 weeks old). I know of someone who had a wild mouse break into their cage, impregnating one of their elderly female mice. She couldn’t accurately sex the babies by 4 weeks old, and a male accidentally stayed with the females. Mum and all the daughters went on to be pregnant, and mum unfortunately passed away whilst giving birth 😢
Once you’re experienced at sexing mice, you can sex them at a few days old…otherwise you’re waiting until the boys are 4-8 weeks old, when their testicles start to very clearly show. The biggest problem there is that male mice can retract their testicles when nervous, scared, or excited…so even then it’s easy to miss and think they’re girls!!
This is the part people don’t want to think about, or believe they can ethically breed without having to cull mice…you can’t.
Let’s start with culling babies.
Mice have anywhere between 5-20 babies per litter; my lines average 12-14 pinkies a litter. In the wild babies have about an 80% survival rate, so these huge litters are important to try guarantee some babies survive…unfortunately (fortunately?) this isn’t a problem with pet mice.
Now, the more babies to a mum, the more strain on her and the less milk (and nutrients) the babies get. A stressed mum means more chance of munched babies, hungry babies, or abandoned babies. Too many babies means individuals miss milk and they get less nutrition overall; babies from big litters will never grow to be as big or healthy as those with managed litters.
Let’s talk numbers. The ideal number of babies for a mum to manage is 4-6. At that ratio the babies get a ton of milk, and mum has a wonderful, enjoyable motherhood!
If you really want, you can push it to ten babies. Female mice have ten teats, so although babies won’t receive huge amounts of milk, it shouldn’t be a problem…but you really shouldn’t keep more than that in one litter. With ten babies you’ll have to keep a very close eye on babies, and check they’re a good weight with milk bellies regularly…if any babies are skinny, you need to reduce the litter.
To leave a mum with a large litter (12, 14 babies) is in my eyes cruel, on both her and the pinkies. Just because litters of 14-18 babies can survive with one mum, doesn’t mean it’s fair – they won’t thrive. It won’t be good for them, and they won’t reach their full potential.
Moving away from having to cull for litter size, you’re most likely going to have to cull to keep down the number of males you have. Males in litters lie 50%, although I’ve noticed mine often sit at 60%. As I said earlier, males can be extremely hard to rehome. Within a few litters you could end up overrun with male mice!
And finally: culling for health.
Please note, all methods we use to cull out mice are humane and veterinary approved.
If you’re breeding mice seriously, you’re going to need to cull at some point.
Breeding mice is a rewarding experience, but you must know what you’re getting into 😉