Rats and mice are polyoestrous and have no specific breeding season. Once bred, mammary development normally occures within 15 to 16 days. A few days before the young are born, a flury of nest building will occur resulting in large nests. The nest should be left undisturbed for 2-3 days after birth. The babies, or pups, are blind, hairless, and immature at birth. They develop rapidly, however, and may be weaned at three weeks.
|Rats||8-10 weeks||10 weeks||4-5 days||20-22 days||6-16||21-28 days|
|Mice||6-7 weeks||7 weeks||4-5 days||19-21 days||8-12||21-28 days|