Poultry encyclopedia · NEXTEKCI School · Feed raw materials
Shells and limestone: calcium
Limestone and crushed shells are the calcium sources in feed. The layer needs large amounts to make her eggshells; the chick and the broiler need much less. Too early or too much damages the kidneys; too little gives fragile shells and weak bones.
Key facts
- Main role
- Calcium (bones, eggshell)
- Calcium content
- Around 35 to 38%
- Highest need
- Layer in production
- For the layer
- Part of it as coarse particles
- Danger
- Too much calcium in pullets: kidney damage
What they are
Limestone (calcium carbonate) is a ground rock; shells are oyster, mussel or other mollusc shells, washed, dried and crushed. Both provide much the same thing: calcium, around 35 to 38% of their weight.
Limestone should not be confused with dolomite, a magnesium-rich rock, which is poorly suited to poultry.
Its role in the ration
Calcium builds the bones of all birds. In the layer, it is also used to make the shell: each egg takes a significant amount with it. This is why layer feed is much richer in calcium than other feeds.
Calcium works together with phosphorus and vitamin D: one does not work without the others. The right ratio between calcium and phosphorus is calculated in the formula by the nutritionist.
The layer: the right time and the right size
The hen makes the shell mainly at night, when she is not eating. Part of the calcium in layer feed is therefore given as coarse particles a few millimetres across: they stay in the gizzard and dissolve slowly during the night. A powder that is too fine passes through too quickly; the hen then draws on her bones, and the shells become fragile.
Timing matters too: layer feed, rich in calcium, is given from the first eggs, after the pre-lay feed. Given too early to the pullet, this calcium damages her kidneys; given too late, it gives fragile shells and exhausted hens.
Quality, storage and availability
Shells must be clean, washed, well dried and heated or dried long enough to remove germs; they must contain no sand, soil or rotting flesh. Limestone must be of a grade intended for animal feed, free of soil and impurities.
In Côte d’Ivoire, there are shells from the lagoons and the coast, and ground limestone. Both are stored dry; they do not go mouldy, but a damp product forms lumps and mixes poorly.
Common mistakes
Giving layer feed, or free-choice shells, to pullets before laying. Giving layers a grower feed that is too low in calcium, then being surprised by thin-shelled or shell-less eggs.
Using dirty shells, sea sand or building lime. Adding calcium to a complete feed "to strengthen the shells" without the nutritionist’s advice: this unbalances the ratio with phosphorus. Fragile shells also have other causes (heat, age, disease): talk to the vet about them.