If your other chickens have the same environment and never have the problem I would doubt it is diet or environmental, sounds more like you have a genetic issue w/ one or more of your houdans.I only wish it was so easy. They flooring was grippy. It was the birds themselves. Even as older birds, several developed twisted legs that turned backwards. I hatch other breeds as well and have never encountered such things. At least one thing I never have problems with is twisted beaks. I am wondering about trace minerals now.