Michael, it never dawned on me til a few weeks ago that if I'm feeding 16% chicken feed and my chickens free range, get treats, and such, their diet really isn't 16% protein is it. Which is their minimum requirement. This thread sure has a lot of micro subjects, and I'm to blame too, not that it bothers me, but there is some really good info in here , and even the off topics can get one thinking about some pretty important stuff.
It depends on what they ingest on range that has nutritional value. Mine range an hour or more a day when I'm home. I rotate between 2 flocks. The way I see it, so long as my birds have good appetites, are at a good weight, have tight droppings, have glossy feathers, and have bright red combs, they are not bearing any nutritional deficiency or disease. I feed a 17% layer ration, a 15% scratch/pellet mixture as a treat, and supply granite grit and oyster shell. I try to supplement a milk protein in feed once a week (usually 1% buttermilk, goat or sheep milk). I don't have digestion issues doing it that way, though I'd recommend doing scant amounts in the beginning when introducing it to diet. I supplement water with vitamins 2-3 times a week, and Probiotic soluble in waterers once a week. I change things up with supplementation depending on time of year, whether or not they are in moult, breeding season, or depending on what I witness in appearance and activity. I handle them regularly to look their bodies over when on the roosts at night.