I feed them all the same. If the moms are producing a lot I add sunflower seeds or mealworms to boost the protein. I have noticed that the pregnant and/or nursing moms do eat a lot more so it would stand to reason that they would poop more too! LOL!
As far as good looking rats, I started with two feeder females I bought as fuzzies for my snakes. When they weren't eaten I didn't have the heart to put them down so I mixed a formula and raised them up. Such sweeties too! Both consistently gave me 15 to 18 ratties per litter will 100% survival of babies. I now have daughters and one dumbo I bought. The dumbo has only bred once and gave me 12 babies. Meanwhile, the girls produced by the first two "pet store" rats have produced just like their moms did. I have a pretty little golden colored girl who just had her first litter yesterday. There are 15 beautiful little ones and she is feeding them and taking excellent care of them.
So, I would say that there isn't a difference between good rats and "pet store" rats, you just have to breed them and the ones who produce well and take good care of their young are keepers while the nervous Nellie’s who eat half of their litters are either pets or snake food.
Good luck,
Marcia 