They really shouldn't be cannibalizing as long as they have plenty of food and water. I'm not sure what kind of rodent block you are using, but I'm buying Kent rat food, $12 for a 50 pound bag and they don't get any dog food. I used to feed them some dog food, but they were getting fat. They are doing perfectly fine with just the rodent food.
If you really want to give them dog food, just get them one of the cheaper brands, that way it doesn't have too much protein. The cheaper dog foods are mostly grain. Cat food has a lot of protein so you want to stay away from that.
The other thing I was wondering is how you are feeding them. Are they eating it through hardwired cloth or are you just putting the food in the tub/tank with the rats? If you are putting it in the tub/tank they are peeing on it which means they aren't going to eat as much of it. And if you are feeding through hardwired cloth make sure it's wide enough.
i'm using native earth 18%, they are eating through 1/2 inch grid wire but i still seem to be getting deaths and cannibals