Calcium Should Only Be Offered Free-Choice
Regarding the letter "Ground Eggshells Add Calcium" (June/July, 2010, page 10), I would like to point out that reader Sarah R. was forcing her chickens to eat the eggshells by mixing them with mashed apples after they didn't seem to want anymore.
The only safe way to give chickens calcium is from sources such as oyster shell or other non-chicken products. Feeding them egg products can be dangerous even though we cannot perceive any problems.
Life forms live in extremely hot temperatures so boiling and/or baking eggshells may never kill everything as we do not know what is still living within. Things can be so tiny an electron microscope will not show us all that is possible.
Charles M., Virginia
According to Gail Damerow, author of Storey's Guide to Raising Chickens, "I agree that a calcium source should not be mixed with other food to force or encourage hens to eat it. Calcium should be offered separately, free choice, so hens can take as much or as little (or none) as they want/need.
"Feeding eggshells back to hens should not be a problem, provided: the hens are healthy to start with, the shells are from fresh (not incubated) eggs, the shell membranes are removed, the shells are clean and thoroughly dry, the shells are crushed."
The following information on calcium, and a useful feeding station example below are courtesy of Storey's Guide to Raising Chickens, 3rd edition, updated and revised 2010; available in the Backyard Poultry Bookstore. Ed.
Calcium
Calcium is 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 Connection
Phosphorus and calcium are interrelated a hen's body needs one to metabolize the other. Phosphorus is a naturally occurring chemical element needed by hens to metabolize calcium. Without an adequate amount of phosphorus, calcium cannot be absorbed and hens may experience calcium deficiency and lay thin-shelled eggs despite the availability of a calcium supplement.
Range-fed hens obtain some phosphorus and calcium by eating beetles and other hard-shelled bugs, but they may not get enough. Sources of phosphorus include defluorinated rock phosphate and charcoal (biochar). The correct ratio of phosphorus to calcium is 1:2. When both supplements are offered separately and free choice, the hens will ingest the correct balance.
http://www.backyardpoultrymag.com/issues/5/5-4/calcium_should_only_be_offered_free-choice.html
