An eggshell is almost pure calcium carbonate, about 2 grams per egg. A hen that lays every day needs around 4 grams of calcium per day (part goes to the body’s own needs). If calcium runs short, the hen pulls it from her own bones, shells get thin, and production drops.
Where calcium comes from
| Source | Pros | Cons |
|---|---|---|
| Layer feed | Already balanced, usually about 3.5–4.2% calcium | Share drops if you dilute it with grain |
| Oyster shell | Coarse particles dissolve slowly in the gizzard | Costs more than chalk; must be clean |
| Crushed limestone | Cheap and available | Particle size matters |
| Feed chalk | Cheap | Fine dust is absorbed quickly and runs out by night |
| Eggshells | Free | Only baked and crushed, or hens may learn to peck eggs |
Why particle size matters
The shell forms at night, when the hen is no longer eating. Fine powder is absorbed within a few hours and is gone by night, while coarse particles (roughly 2–4 mm) stay in the gizzard and dissolve gradually — exactly during the night. So give shell and limestone coarse, not as dust.
How to give it
- In a separate feeder, free choice, so each bird takes what she needs. Laying hens are fairly good at sensing their need.
- If you feed a complete layer feed, the extra is only support — coarse oyster shell in a separate feeder.
- If you feed grain and mash, calcium is a must, and so is protein — otherwise shells will suffer.
Grit
Hens have no teeth; the gizzard grinds food with the help of small stones. Free-range birds find them on their own. If your hens live indoors and eat whole grain, give them small gravel separately. It is not the same as shell: shell is a calcium source, grit is the “millstones.”
When calcium does harm
- Chicks and pullets before they start laying. Excess calcium in the feed of growing birds is hard on the kidneys. Switch to high-calcium layer feed when the first eggs appear, not earlier; a pre-lay feed is fine before that.
- Roosters and non-laying birds do not need much calcium.
- Vitamin D3 overdose is also dangerous. Do not raise the doses of preparations without a vet.
For calcium to be absorbed, you need vitamin D3. Complete feeds contain it, and free-range hens get it from the sun. In winter in a closed house on a “home” diet there may be too little.
Watch the eggs
The best indicator of calcium is the shell. If breakage and thin shells grow week after week, check the diet before production falls. For other possible causes, see the article on thin and soft eggshells, and for how much to feed overall, feed norms.
