What does your feed look like? Is it a homogenised pellet or crumble or more a whole grain feed? If the latter, this may be your problem. With grain feeds, the chickens can pick individual components out of the feed that they like best. These are often the high carbohydrate grains and they leave the higher protein lentils/pulses for other birds to eat. There have been a number of posts here on BYC where people's young birds have suffered a similar fate. You might as well be feeding those birds scratch every day, because essentially those are the things that they are picking out of the feed.