I just recently read Gail Damerow's Hatching and Brooding your own chicks book. There is a piece that I want to pass along to you all that are having problems with shelless eggs:
Calcium in needed by laying hens to keep eggshells strong. The amount of calcium a hen needs varies with her age, diet, and state of health; older hens, for instance, need more calcium than younger hens. Hens on pasture obtain some amount of calcium naturally, but illness may cause a calcium imbalance. In warm weather, when all chickens eat less, the calcium in a hen's ration may not be enough to meet her needs, and a hen that gets too little calcium lays thin-shelled eggs. On the other hand, a hen that eats extra ration in an attempt to replenish calcium gets fat and becomes a poor layer.
Eggshells consist primarily of calcium carbonate, the same material found in oyster shells, aragonite, and limestone. All laying hens should have access to a separate hopper full of crushed oyster shells, ground aragonite, or chipped limestone (not dolomitic limestone, which can be detrimental to egg production).
Phosphorus and calcium are interrelated- a hen's body needs one to metabolize the other. Range-fed hens obtain some phosphorus and calcium by eating beetles and other hard shelled bugs, but they might not get enough. To balance the calcium supplement, offer phosphorus or charcoal (biochar). The correct ratio of phosphorus to calcium is 1:2. When both supplements are offered separately and are available at all times, hens will ingest the right balance.
I give my hens free choice oyster shells but they don't seem to like it, so I started mixing crushed egg shells in their treats and they are eating them. I have been thinking about putting a little container with crushed charcoal free choice and watch what happens, I believe Gail Damerow is an authority in chickens' keeping and has a very long experience so I value her opinion.
