Quote Originally Posted by Brandon Osborne View Post
They should be at least 28 days old and around 25-30 grams.
Am I reading this correctly that you pair up your mice when they are only 28 days (4 weeks)? Some people don't even wean until then.

If you do put the females with males so young, do you have any issues with them getting pregnant so young? People report all sorts of problems ranging from small litters and young mothers being more likely to cannibalize their young all the way to losing both mom & babies because it was more than her young body could handle.

I wouldn't be surprised to find out that good strains of mice with a good diet, etc, can handle being bred at a younger age than in less ideal situations, but 4 weeks still sounds young to me so I'm curious what results you have seen with it.