When a mouse is born, he can’t do much to defend himself -- he’s blind and deaf, and therefore unable to navigate his environment or find his own food. Fortunately, his mother is there to take care of him. If she doesn’t assume responsibility for feeding him, someone else has to, or he won’t survive.
Just like larger mammals like dogs and cats, mice give birth to litters. A female mouse typically gives birth to a litter of five or six babies, though she can actually give birth to more than a dozen. It’s her responsibility to care for the babies when they are born, because the males don’t do anything to help raise the young. Because the gestation period is so short and a female can breed again immediately, she can give birth to as many as 10 litters per year -- quite a few little mouths to feed.
When the baby mice are born, they’re completely deaf and blind -- they won’t be able to see or hear for more than a week. This means that during that period -- and afterward -- the mother is solely responsible for feeding her young. They feed at her teats, which they find by feeling their mother’s warm body blindly.
Nursing a Mouse
If a mother abandons her young or dies, they need to be fed, either by a foster mouse, a foster rat or human hand-feeding. Mothers already nursing babies of their own are typically willing to take on fosters -- rats make especially-willing foster mothers for mice. By removing the mouse or rat mother from her babies and then rubbing her natural babies in your hands with the orphans, you make the two litters indistinguishable to her.
Though they are tiny, baby mice have big appetites -- the babies eat about once every two hours, so if you take on feeding duties yourself, you have to diligently monitor the time. It takes a baby mouse about five minutes of feeding to get his fill of milk or formula.
Even after the babies open their eyes, they continue relying on their mother for food. They can see and hear when they are about 10 days old, but their mother feeds them until they are about three weeks old. By this time, their teeth have started to grow in and they can be weaned off of the teat and onto solid foods. By the time the babies are four weeks old, they’re completely independent.