We just starting getting eggs from one of our 18 week old hens this week. I am switching from start and grow feed to layena feed. I also added some oyster shell in a pie tin in the chicken run. The next day the entire dish of oyster shell was gone. Is this normal? I read that they will eat what they need to supplement their diet. Will eating that much hurt them? Should I add more to the tin? Any suggestions would be appreciated. Thanks.