I've had my rats on dog food for years and that's never happened for me. If that is happening chances are the mother isn't getting fed enough.
If you want to use rat blocks, you can have your local Tractor Supply store order some for you.![]()
As for dog food, I use a cheap brand called "Doggy Bag" it's like 6$ for a 40lb bag; you can get it from Tractor Supply. I prefer that brand because of the kibble size which is the size of a marble. Sounds strange but I find that my rats waste less food because of the kibble size being so big.
One thing you should look at is the crude protein on the back of the bag, from what I've read the best dog food for rats has a crude protein level around 15%-18%. The brand I use is 18%. If the protein is too high, the rats have a tendency to loose their hair.