Outof my 3 1.5 colinies only 2 of them keep producing babies, the 3rd one produced 5 litters, one from each female but after that there is no action. I'm thinking about replacing the male, maybe he got in to a fight with one of the females or something.

At what age should I introduce the new male? Is weanling size enough or should I wait a few weeks more?

Thanks
-D