I don't feed layer feed to my young chickens. I've been doing this for years and years and never had one just up and die. When they die it's by my hand alone. Layer feed has no effect on roo's at all. All the studies you read are USDA standards. Which in my eyes are full of holes.
Facts: In the United States,
USDA free range regulations apply only to poultry and indicate that the animal has been allowed access to the outside.
[3] The USDA regulations do not specify the quality or size of the outside range nor the duration of time an animal must have access to the outside.
Most companies that calm they have free range chickens have a door the chickens can't even get out of. Open it up and call there chickens free range.
Layer feed has so little calcium in it. Every animal needs calcium for strong bones and a lot of other heath reasons. Again I'm not talking young chickens. And if the females are too old to lay eggs there in the freezer. So I don't see the problem here.
I think a lot of people try to become scientist and biologist here. REALLY. We are all talking about CHICKENS HERE!!!! I will say it again. Don't over think how to feed them, warm them, water them. There chickens for god sakes. When I first started raising chickens I tried to hard to keep them safe, clean water and boarding them up on cold nights. I had a terrible time keeping healthy chickens. Once I realized they were just chickens and i let them be chickens I now have the prettiest and healthiest chickens around. It's a wonder the forum is so full of problems.
When you become a chicken owner you now have a small farm. On farms guess what, you will have problems and they will be moralities.
Just the fact of life. I just think people are over thinking to much is all. Sorry if I went off on a tangent. But I had to learn the hard way of over babying my chickens. It's not good for them. I wish people would understand that. All would be better off.