There's a lot of garbage out there marketed to the soccer mom, fur-baby crowd. Grain free this, organic that marketing BS. I raise and train performance dogs and feed what almost all of the top retriever and pointer field trial trainers feed.
If you have a working dog, feed a quality 30/20 feed from Victor, Purina or Eukanuba. My working labs get 3-4 cups a day.
If you have a couch potato house dog, feed the same thing, just less of it so Fido doesn't become obese, like most pet dogs. If you get down to 2 cups a day (for a 50-75 pound dog) and he's still fat, drop to a lower protein/fat food. But avoid the designer labels and grain-free formulas. Just feed good feed from an established company with a long track record.
It ain't rocket surgery. Don't overthink it.
I have run all age pointing dogs my whole adult life. and about 40 years ago I did the research from ground zero to see what would help them out. It came down to roughly 20% digestible protein and 15% or so fat with the rest made up in carbs. Supplement with fat and bump the supplements when the dogs work a lot. Feed an extra meal at noon on work days to get enough calories into them to keep them going. For a machine like an all age pointing dog you basically need to feed them like a Tour de France racer. Get as much calories in easy (quick) to digest carbs into them as they will take and keep the protein down to a minimum because it takes too much water through the kidneys to get rid of the nitrogen, and when the go low on water they overheat in a hurry and the consequences of that are not good on a dog carrying about zero fat. Fat and carbs are very helpful. Converting protein to energy is water intensive and getting rid of the by products of that conversion takes more water if you want to avoid damage to the dog.
Purina maintains that dog food research lab down in Iowa for a very good reason and they do some damn good work there.
