My chickens are just about a year old. Everything I read regarding Oyster Shell said to either put it in there food or give it to them in their coop/run so they can eat it as they want so I am hoping that means not matter what they didn't get too much yesterday. I am just giving it to them like I would scratch now, sometimes mixed in with the scratch. I am going to give them so cottage cheese later or yogurt to help. I did get an egg earlier today and it seemed good, no weak shell.
Sounds good I def noticed a difference after I started giving them cheese and yogurt. Plus I have noticed that in the winter when they get less protein (cause of the lack of bugs) the shells get thinner. I give mine either dried mealworms or live ones if I can find them. I also go to the pet stores and buy live crickets the chickens love them. the protein also seems to help thicken the shells