Different age dogs need different nutrition regimens.
It's imperative that puppies get lots of calcium, while older dogs don't need as much. Other variables include sex, breed, purpose (show, hunting, etc.), all of which must be considered when balancing your dog’s diet. Several things, however, are common to all dogs, all ages, both sexes, and all purposes, including lots of proteins, grains, fats (for a shiny coat), etc. The problem comes, however, with all these “special formulae for improved health (and/or appearance)” foods for regular, average adult “house” dogs. Is Purina really better than Chow? Is Chow that much better than Ol’ Roy?
Okay, so let's take something like Purina Puppy Chow (or any other “for puppies” food). As the name implies, it's specially formulated to provide a balanced diet to puppies (and nursing adults) by being heavy in calcium. There are special foods for older dogs that have more protein. In fact, some dogs with kidney problems have to eliminate certain kinds of minerals and ingredients from their food. They can only eat one particular balance of nutrients--nothing else.
Just like athletes who need to eat lots of carbohydrates and very little fat in order to perform at their maximum level of efficiency, some dogs need special varieties of food. You wouldn’t feed a dog which was about to run the Iditarod the same as you would feed a dog about to go on a hunt the same as you would feed a nursing mother the same as…. So for specialized areas (performance, nursing, or health conditions) dogs need specially balanced foods. As far as health, though, no one brand is better as long as they are formulated according to the same balance of nutrients, minerals, carbohydrates, proteins, etc.
By far the majority of grown, adult dogs (with no special needs, including maternity) will be just as well off eating the generic “Wal-Mart” brand as they will “Purina Special Formula.” Again it’s not so much the brand of food that matters, but the balance of nutrients. The brand adds price and, generally, better taste (real beef and chicken extract!), but in the long run, adds the only price and not benefit.
Regular house dogs will generally be just as well off with one kind of food as another. There is no “special” or “magical” formula that will make your dog live longer, nor will a lack of any type of food (for the average dog) greatly alter the balance of your dog’s health and happiness. Much depends on life-style. If your dog isn’t healthy, look first at its exercise regimen and then at its diet (including table scraps). If changing one and augmenting the other doesn’t work, see your vet. Your dog may have a special need or health problem that can’t be addressed by any brand or type or formula of dog food, no matter how “special” or expensive.
Obviously this article isn't going to tell you everything you need to know about pet nutrition; for that, you should see your vet--they know best. However, from years of experience (and occasional fretting over my dog’s health), I give you the best advice I can. Dogs with special needs need special food—and you should spare no expense to get them what they need to stay healthy. But, conversely, know when you can get your dog the same benefits for a smaller price. In this way, you balance not only your dog's diet but also your checkbook.