I have had birds for 18 years, but I'm lost at this point. We have ALWAYS fed 15% layer feed with scratch (1 cup) for a treat. The layer feed was available 24/7. However, birds started dropping dead and the ones that dropped dead were either RIDICULOUSLY heavy or were as bony as a starved bird so we switched the feed to a different source. We have SINCE switched to 16% layer pellets, 1 cup of scratch, BOSS and 22% grower mixture. (Available in a metal feeder 24/7.) My birds are so skinny, I'm afraid of them dropping dead. I just don't understand it? All the birds are different breeds including Langshan, Cochin, Minorca and Black Australorp. Odd thing is...only 1 of the bantam chickens is affected. The other 3 are a nice healthy weight with no sign of a concave breast. They are not allowed to free range because of predation (neighbor's dogs...). What am I doing wrong and how can I fix it?