If you buy a 40-pound bag every week, your dog's food only needs to make it from the store to the bowl. Because of the rapid development of bone and muscle mass during this time, and the breed's propensity for such problems as arthritis, OCD, and dysplasia, it's important that these dogs receive protein and calcium in quantities that are just high enough to allow development. I also make treats for my dogs. I use recipes that don't have many ingredients, because I like to know what they're eating. I mix in lots of different things, to add variety.
Dogs have definite likes and dislikes, just as people do.
Generally speaking, you get what you pay for . If you feed an economy food, chances are there is very little in the way of usable nutrients available in what you're feeding, so you have to feed your dog alot more of the economy foods than you would if you were feeding the premium grades. Since switching to a super-premium brand, my dogs are eating a total of 5 cups, daily. She just wasn't interested in eating the amounts required, before. Now, she's able to eat enough to satisfy her physiological needs, because it takes MUCH less.