You should be able to easily create healthier rodents by selecting out any that have health problems. On the other hand, you can try contacting better breeders, and seeing if you can get healthier mice. Ann Marlowe is in your area, and is a very good person, with great mice.

I'm actually going to MD this Sunday for some mouse related stuff. I have a few (max 2 or 3 that I was going to use as feeders) females and a male I can throw your way if you can be in the Silver springs area? They would be a really great way to start a colony, they have very varied genetics from all over the world, and are very healthy mice, I just don't need them for my projects lol.