When Iams was first brought to market it WAS a great brand of dog food. It was good quality with little fillers. Then someone else bought the company and now it's crap and full with fillers and other garbage. Not to mention all the abuse they do testing it on animals.

but even if I did I would usualy just buy whats on sale .
You wouldn't be able to keep switching their diet like that, they would become extremly sick.

Hills Science Diet
That's another brand that has lots of fillers and is a very cheap brand of dog food.