Quote Originally Posted by kc261 View Post
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.

4 week is too young. most of the time their bodies aren't fully developed yet so if they get prego at 4 weeks it makes them sick and stunts future growth. In my experience they get to looking anorexic after giving birth and never gain the weight back.

Safest bet is 12 weeks for optimum health, but you can put them together younger if they have reached a mature size and weight.