I have been raising chickens for about a year and have not had any issues with my eggs. I recently decided to let them free range in my yard. It was just a few weeks later and I started to get fragile egg shells. Thin and easily damaged. I realized that they weren't getting the calcium that they needed. I returned them to the coop and run and upped the calcium and the eggs got better. I think I discovered that when free ranging your chickens you need to make sure they have access to the nutrients they need, including proteins and calcium . Mine spent to much time feeding on the grass and whatever else they could find, but they weren't getting what they needed. Hope my recent experience helps