I feed my birds anything and everything that is unfit for human consumption, unless it's more than two colours, fuzzy enough to pet, or unidentifiable. I do not have issues with birds dropping dead or being in ill health. They free range and have layer pellets or molasses grain available at all times. A bit of a non-standard approach compared to everyone else on here, I know, but eating 'everything but the kitchen sink' is one of the reasons why I have chickens. Flock size might matter---with 50 birds, anything that might be potentially toxic gets spread over a large number instead of 3 birds able to eat at leisure.
Again, I'm not going to recommend this approach over the scientifically backed one, but I figured I'd mention it because it works for me and my flock.