Dr. Kelly Swanson, an Animal Sciences professor at the University of Illinois College of Veterinary Medicine, explains why dogs can get the same amount of nutrition from both lower cost and premium dog foods.
"The main difference among the myriad options lies in the ingredients used. Specific diets, such as 'lamb and rice,' indicate that a primary protein source is lamb and a major carbohydrate source is rice.
But what constitutes quality? That may be a matter of opinion. There is a difference between lower cost foods and the 'premium' or 'super premium' diets. Premium and super premium tend to be more nutrient dense and have better digestibility. Better digestibility can mean fewer 'restroom' trips and possibly less gas. Yet that still doesn't mean that your pet cannot get all the needed nutrients from a lower cost diet." I take that to mean there's some advantage to buying the best you can afford; but your dog will be fine on ordinary food.
She also explains that the term "natural" can mean just about anything and natural foods are not regulated, while organic foods must meet USDA standards.
Here's the part that will make many Airedale owners laugh: the important thing is that your dog likes the food. I've heard of the rare Airedale who is picky but about the only food my Airedales have ever refused is iceberg lettuce. I don't consider iceberg lettuce as food, either.
Source: An article from the University of Illinois College of Agricultural, Consumer, and Environmental Sciences (ACES) Thoughts On What to Feed Your Dog.