Saw this post when coming onto the forum to ask if anyone else's chickens go off pellets/crumble after eating them for a few years. I'm about to throw out two bags and find other brands to try 
Not only are our girls picking out wheat or oats from their crumb/pellets, each girl has their preferences.
I try to give them a big batch of random garden greens in the morning (some things are eaten, others are not) and hand feed some sorrel or chicory in the afternoon. Of which, two girls will only eat the stems and the other girls will only eat the leaves.
I think they prefer grass, bugs, and sparrow poop to everything but peanuts.
Do chickens have an incredible scent or taste ability? Some things they know to turn their beaks up at before even trying it and other things they find in the dirt they have to toss around in their mouths before deciding if it's edible.