This from a question about calculating protein in a homemade ration:
Standard laying mash is around 16 – 18% protein; that’s what they make for commercial producers and backyard chicken keepers aiming at a very high rate of lay.
This is at least in part because modern hens have been selected for maximum performance in the short run, not longevity or duration of lay. It takes a lot of dietary protein to make an egg. Today, the commercial goal is to get at least 300 – 330 eggs per hen in her first year of lay, then sell her to Campbells; in the typical backyard flock, same genetics, you might keep her around for a second year if you don’t mind much reduced performance. After that, the soup pot.
In contrast, eighty years ago a hen was considered a good layer if she gave 200 eggs per year, and she was expected to lay for several years.
If what you want is an accelerated rate of lay, you’ll need to supply a lot of protein. But if you’re going to pasture or free-range — which is what it sounds like you intend to do — then you’re probably electing to go for a more natural rate of lay, which leaves more latitude in the matter of how much protein supplement you provide.
Now, if you were really setting out to determine precisely how much protein you needed to reach 18% of the birds’ diet, you’d have your work cut out for you. First, you won’t know what the birds are picking up as they forage, so you can’t know its food value. Secondly, the percent protein of those bulk foods (like corn, wheat, oats) with which you make up the majority of their ration can vary a great deal from batch to batch, depending on a lot of variables, so you’d actually have to test each batch of grain you purchased or grew to determine its composition. Only if you know all of the variables can you calculate with accuracy the amount of milk or other protein you need to raise your total ration to the 16 – 18% rate.
Fortunately, it’s not really that hard to get a satisfactory ration without all of the numbers.
You say you would like to switch to ‘grass and natural feed’ for your flock. Let’s assume that means you’re going to free-range or pasture the birds, while providing some kind of grain ration. Corn and most of the cereal grains average well below the minimum recommended percentage protein, but they’re good for some protein and for plenty of carbs. With dry grain rations, it’s generally considered that a hen of average size needs about one-quarter pound of feed per day, and somewhere around that’s not a bad place to start. 18% of 4 oz. is 0.72 oz. protein, and they’ll get more than half of that from their grain and whatever they pick up foraging, so if you offer a high-protein supplement like curds or waste meat, which are about 25% protein, an ounce of one of these per day gets your birds’ ration up in the high-protein range. For visual reference, that’s a lump about the size of a hulled walnut, or rather smaller, per bird.
All that said, in the summer a free-range bird with plenty of pasture (not bare soil) to range about in is going to pick up a lot of bugs and worms, and might do very well without protein added to her grain allotment. And since she’s free-range, she may also hide all her lovely eggs where you can’t find them.
The practice of farming has more in common with dancing than with science: if you want it to be beautiful and enjoyable, you pay attention to your partner and respond to changes in the rhythm.