I also try to stay away from dog foods as a primary diet. Most cheap dog foods contain dyes and such that are not good for the rats. Too much protein and fat can cause just as many health problems as not enough. I haven't been breeding my rats long; only since the summer, but I've had good results with my rat diet.

I feed Purina Mills Natures Match Sow and Pig pellets. I get 50lbs for about $13. I also get discounted, low protein dog food from work (usually no more than 25%) that I use as a supplement for pregnant and nursing moms (they get a small scoop of it every other day or so). I also will give dry and cooked pasta and sometimes fruit and veggie scraps. The pellet food when fed along with the supplement kibble and such will last me about a month (100lbs) for the three racks I have. The only downside to the pig pellets is the high waste due to the fact it crumbles and is too small to sit on the mesh. I plan on making the switch to Mazuri soon as it costs about $25/50lbs and there will be a lot less waste.

I get good results with the pig pellets and dog food supplement. My litters are usually around 12 or so with good fat babies. I plan on doing a comparison soon, if I have the time, of litter size and weights when fed the pig pellet and dog food mix as opposed to the mazuri.