American Fancy Rat & Mouse Association

This article is from the Spring 1999 AFRMA Rat & Mouse Tales news-magazine.

Breeding & Stuff

Breeding Age of Mice; Simultaneous Estrous?

Kathy Madere, Amite, LA
QWe have several females in with one male. These mice are at present approximately 8 weeks of age. No young have been produced as yet, although I have hopes that two or three are pregnant. How old are your mice when they begin breeding? One female in this group has been with the little male since birth. Is this an unusually long time for these animals to breed? They’ve all been together several weeks now.

AMice are capable of getting pregnant as soon as 6–8 weeks. (There have been some cases of mice getting pregnant as soon as 4½ –5 weeks of age.) Although mice can begin to breed at 6 weeks, I would not recommend breeding until 8–12 weeks of age. With the English show mice, the recommended time to breed for the first time is 12 weeks. If bred too young, the animal can suffer physical and mental stresses that in turn make her a poor mother for her first litter, then the kittens suffer as well.

Female mice come into season (ovulate) every 4–6 days. This estrous time lasts about 12 hours where they will be willing to mate with your male. After your male successfully mates with the females, you may see a whitish plug in the female which will last about 24 hours. The normal gestation period is 19–21 days. Always remember, if you leave your male in with the females when they give birth, he will breed them immediately to within hours after they deliver and they will have babies again 3 weeks later while they are still nursing the first litters. This is normally not recommended with the show animals.

There will be on average, 8–10 babies per litter so make sure you have plenty of cage space if you leave all the females in the same cage together to deliver their offspring. Mice are usually very good about sharing in the raising of each other’s babies, having a community nest where each mother will take turns nursing the babies.

Simultaneous Estrous?

QDo female rats that are housed together go into heat at the same time?

Rat in season

AI have two large tanks in the house with three females in one and four females in the other. They each have their own cycle. Almost every night one of them is in season. *

Back to top

Updated February 14, 2015