I would not recomend feeding dog food to rodents. I work at a pet store and we started feeding returned dog food to our rats and mice. After about a month we started to notice them getting sick. The protein and fat levels are too high. Even though brands like purina and science diet have high grain levels (which isnt good for dogs) theres just too much crap in them that makes it un healthy for rodents.

Try and find bulk bags of rodent food. You should be able to fing Kaytee rodent pellets in 20 pound bags for around 25 bucks