I would like to comment in regards to "new blood." I have four colonies of mice and when it is time for "new blood" I take babies from one colony and add to another colony. I have never had a problem with a colony accepting new babies as long as the babies still have their eyes closed. This is easiest if you have colored babies so you don't accidentally feed off your new breeding stock. It has worked well for me and avoids any problems with bringing in new blood. If all of your colonies are related, you can also buy fuzzies from the pet store to add. Good luck!!