Hi:
I have been feeding my chickens the Purina layer crumbles or the Tractor Supply layer crumbles (16% protein). I tried the pellets once but the chickens did not care for the pellets. When they are laying I also give them a grounded oyster supplement. This is just added calcium to their diet. My chickens are totally free range so they are eating items that are not found in the crumbles feed. They love just about any insect. I even had one take down a vole. The chickens I have now are going into their second year and are strong layers. They lay right through the winter but the production is lower then, it picks up as the days get longer. Many people kill their chickens at around 18 months and get a new flock because they feel that production goes down. It may go down on birds that are kept in a coop all the time but I have had birds that are still going strong at 3 or 4 years. I feel that being free range may contribute to being strong producers.
I add chickens to my flock every two years or so. I do lose some birds to predation (bobcat and foxes) but as least they went out happy doing what a chicken likes to do, going all over the place scratching up a storm. By having them free range I do not use a lot of feed during the year. Also, I don't have any problems with the health of my birds.
If you keep them through their molt (usually 12 to 16 months of age) you may have a bird or two that begins to walk around like she is drunk. When they molt their protein requirement is very high as they produce new feathers. Give them cheap hamburger and they will do fine in a day or two.