I have taken the time to design and research poultry grits made from calcium carbonate sources.
It is written in the MICRONA Poultry Grit flyer :
http://gardenpearls.com/wp-content/uploads/2012/12/MICRONA_Poultry-Grit-Flyer.pdf
that A. Bruce Webster, Extension Poultry Scientist, University of Georgia researched this and he explained about calcium carbonate grit as a suitable source of calcium for chicken. While we must offer chicken and other birds hard pieces for their crop - we can use granite as a digestion aid. But oyster shell is a calcium source. We now know that the mineral calcium carbonate in grit form at various sizes is well accepted for chicken and other foul. It is used as a single grit and calcium source but sometimes also used in combination with granite and oyster.
Ideally, we would really like to keep our chickens and ducks truly 'free range' so that they can find enough of their own rock grit and calcium sources such as dark green leaves and vegetables, bugs and worms. However, I struggle for space to be able to do this and I think most of you do as well. We have lost too many chicken to neighbors dogs, coyotes, and eagles. Flint grit, oyster shell and MICRONA Poultry Grit Calcium Carbonate is really not expensive. Our modern birds require a lot of calcium that even a large back yard cannot supply. One hen requires 8 lbs of Poultry Grit per year - and they will "recyle" the particles as well. A 50 lbs bag will last a long time so it's a good idea to provide this for hens, especially because most of the birds have lost their freedom to roam for their own safety.
Another way to see the viability and usefulness of poultry grit came when my friend noticed that song birds would pick through the MICRONA Poultry Grit for smaller calcium particles. Obviously, they need this too to stay healthy when making eggs in Spring.
Referring again to the need of calcium carbonate Poultry Grit, read the research article at :
http://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=2097&context=etd I don't think it is "double talk" to have the dual benefits of calcium carbonate grit.
"Calcium provided as coarse particles can improve egg shell quality and bone strength (Scott et al., 1982; Fleming et al., 1998; Scheideler, 1998; Whitehead and Fleming, 2000). The coarse-Ca particles are solubilized more slowly from the gizzard than fine-Ca particles which allows the hen to absorb dietary Ca at night during egg shell formation. This absorption can result in less Ca mobilized from bone stores (Scott et al., 1971; Zhang and Coon, 1997; Whitehead, 2004). Calcium is also necessary for the release of gonadotrophic hormones, including the surge in luteinizing hormone that results in ovulation necessary for egg production (Luck and Scanes, 1979, 1980; Johnson, 2000)."
Larger size calcium carbonate chicken grits such as the MICRONA Poultry Grit 6x10 are found to be especially beneficial for older hens. The calcium particle remains in their digestive system over night and helps pull calcium form the mineral instead of the bones and joints of the chicken. If you have those treasured hens that are laying large but often soft shelled eggs, poultry grit on calcium basis can be a good supplement; in research it performed better than oyster shell and granite grit for mature layers.
Hens sometimes need a bit of time to adjust to a new grit source and require transitions to get used to calcium carbonate type grit. Our oyster shell consumption went down drastically after a few days of adjustment and we only need a potion of the quantity of total oyster shell used before.
The MICRONA Poultry Grit is available in local farm stores in Eugene, OR for about $10 for a 50 lb bag. It probably is higher in cost if it is mailed out or shipped.
To support our feathered friends with added health and good digestion including getting them sources of available calcium from oyster shell and limestone calcium carbonate (other than drawing from their own bones), many recommend to add a squirt of apple cider vinegar to the drinking water on occasion (once per week) that is what we have been doing.
AlohaDuck was looking for calcium source for egg laying ducks. This is unfortunately not well researched in our country. I love to eat and cook with duck eggs! Duck eggs are a cherished source of food in many Asian Nations and they have a huge requirement of calcium to lay good eggs and not become ill due to m
alnourishment.
Extension bulletins are a great resource:
http://www.extension.org/pages/71081/nutrient-requirements-for-organic-egg-laying-ducks#.VM2MU2jF-So
A ground, round high purity calcium carbonate limestone grit, given free choice in a feed dish, on the stall floor or in the outside run, is a vital part of our birds life. But in my perfect world they should have enough space to run (where any grit and particles can be picked up), good clean (vinegary) water, good food from a reputable feed mill and access to fresh greens.
Poultry Grit is derived from calcium carbonate. As a grit source, it is superior to oyster shell – shell is not hard enough to do the digesting task grit will.
