We just leave oyster shells out in a little bowl for them, seems to come and go in phases if they are eating it or not, never been able to put a pattern to it. The feed has claclium in it. I tend to think it has to do with them being out most of the time when the weather is good and not eating much feed. No proof though. Although chickens are omnivores, meat and meat byproducts shouldn't be a regular proline source for them, mostly because of the high fat content. Not withstanding, ours get meat too, just not a steady diet of it.
