Thank you for this in-depth and well-illustrated article! I've been going nuts trying to find out why one of my young hens started laying shell-less eggs regularly while all the others (same age) are laying just fine. They are all getting plenty of calcium and D3 in their rations and oyster/eggshell supplement dish. This makes me suspect it's because some are starting their first molt so it's probably one of those girls. Lots of great info and references here, thank you so much!