They aren't as delicate as people believe. I've been feeding chicks layer ration and roosters layer ration for many years now....my chickens live to a ripe old age before they are culled due to finally stopping lay. They are healthy, hardy and vigorous all their lives. I've never had illness in my flocks and I've had exceptional laying all these years. People have to keep in mind that calcium is not a mineral that just is used in egg laying....bones need calcium to stay strong and as one exercises, calcium is moved from the blood stream to the bone matrix to support the tug and pull of the muscles against the bone. My birds are high performance birds that free range at all times, all year round, so they are constantly exercising, putting stress against their bones through the use of muscles being worked, so dietary calcium is not being filtered through the kidneys to be excreted as much as birds that are sedentary. Roosters are much more active than hens as they have to chase, subdue and breed all the hens and patrol the area, find food for the hens, run off other suitors, etc. They use far more calcium than is ever used by a hen in the act of laying.
If you have sedentary, penned birds it's a good idea to keep the calcium lower to avoid problems. If you have high performance, active flocks, the calcium is much needed to support that level of activity. The legumes, grasses, and bug chitin my flocks consume are far higher in calcium than anything found in a layer ration and for many months, that forage is the bulk of their diet with the layer ration forming merely a supplement to that high calcium diet.
