Prior to someone saying around the 1930's "Hey, you know what we can do with all the leftovers from butchering these cows?" all pet dogs had to eat were table scraps and what they could catch themselves. Their lifespans then were typically twice what they are now. Commercial dog foods are basically "junk food" much like feeding potato chips to your children for dinner. When I switched my dogs to Biologically Appropriate Raw Foods (BARF) I tried hitting up the local butchers for their leftover raw meat and bones. Guess what they told me? They toss it all in a dedicated dumpster and when it finally gets full they call the company that picks it up to deliver it to..... commercial dog food manufacturers. They might only pick up once a month.
BARF, the acronym and the diet, is the subject of several very good books on pet nutrition. Basically, you mimic the diet your pet's wild ancestors ate. There's even a website, barfworld.com if anyone is interested in learning more.
Major benefits to feeding BARF to my dogs include better mental focus which contributes to faster learning, shinier coats, brighter eyes, fewer veterinary visits, no need for flea and tick control products, stronger muscles and longer lives. Simply put, a much healthier animal.