It's not true that working foods have to be fed only to working dogs. I know plenty of pet dogs or dogs who only go out maybe once a week or so during the shooting season who thrive on 'working' brands such as Skinners, Chudley's, Autarky etc. I feed my dogs Arden Grange but if they weren't on this then Chudley's Working Crunch or Skinners Field and Trial Maintenance would be the likely alternatives. If he's doing well on the food then unless you really see a need to change him I'd keep things as they are. Some of the varieties have higher protein contents but each of these brands does a number of varieties for dogs in heavy work, dogs in the off season etc. and puppy foods always have higher protein levels anyway as puppies require it. The main difference in 'working' brands and a lot of regular ones is simply that they're cheaper as you don't pay VAT on them.