Calcium and oyster shell for layers in Ghana: how much and when

Why one eggshell needs about two grams of calcium

Here is the blunt version. An eggshell weighs about five to six grams and is mostly calcium carbonate, which is around 40 per cent calcium by weight. That puts roughly two grams of calcium into every shell. A hen that lays one egg a day has to find that calcium every day, on top of what her bones and body functions use.

Most of the shell is built overnight, when she is not feeding. The mineral goes on in the later hours of shell formation, so calcium that arrives only at breakfast is not much use for that egg. Timing matters as much as the total.

A hen eating about 110 grams of layer feed a day needs roughly four grams of calcium from her whole diet. Most layer mashes are formulated to supply a good share of that, but the figure on the bag only helps if the hen actually eats the bag. When intake drops in the heat, calcium intake drops with it, and the shell is the first thing to suffer. Our layer feeding guide sets out the calcium level for each phase, and our guide to how many eggs a hen lays shows how much output the shell has to support.

Oyster shell, limestone and the rest: the sources compared

Oyster shell is the calcium source most farmers use, and it is usually the best value for layers. It is calcium carbonate, it is cheap in the coastal towns where oysters are harvested, and it releases calcium slowly in the gizzard, so hens take it in when they need it.

Limestone does the same job if it is clean and properly graded. Crushed limestone varies a lot between quarries, so ask for the analysis and check for sand and dust. Some farmers also use crushed snail shell. Its quality depends on how well it has been cleaned, dried and crushed, and its calcium content is less consistent, so test a sample before you commit to a bag.

Do not feed raw eggshell back to the flock. Shells from your own eggs or from the market can carry Salmonella, and a hen that eats them can pass it on. If you want to recycle shell, boil it, dry it fully and grind it, then treat it like any other calcium source.

Coarse or fine: particle size decides how long calcium lasts

Particle size matters more than most farmers expect. A hen's gizzard holds coarse particles and grinds them slowly, so the calcium releases over a longer period. Fine powder passes through quickly and gives a short, sharp dose. For layers that is the wrong pattern. You want a steady supply that is still in the gut when the shell is being built overnight.

Our rule of thumb for the feeder is a coarse grade, around 2 to 4 millimetres, something like small gravel rather than dust. Keep a fine grade for mixing into mash if your ration calls for it, but never use fine powder as the only source of shell calcium.

When a bag arrives, check it before it goes in the store:

1. Pick up a handful and look for dust. Dust settled at the bottom of the bag means poor grading.
2. Look for sand, stones, and any shell that is damp, grey or smells sour.
3. Ask the supplier for the calcium percentage, on the bag or the invoice.
4. Store it in a lidded bin or a sealed bag, off the floor and away from the wall.

Offer it free choice, in a separate feeder

The way you offer shell matters as much as the grade. Put it in a separate feeder with a lid or a raised dish, so the birds can take it when they need it. Hens are good at regulating their own intake. A hen laying a strong shell takes little. A hen starting to lay thin shells takes more, and she does that on her own, as long as the shell is there.

Mixing shell into the mash by hand sounds tidy, but it fails in practice. Every hen gets the same amount whether she needs it or not. Shell settles to the bottom of the mash and gets sorted out by the birds. And when the mash runs out before the shell does, the flock goes short in the afternoon, when the shell is most useful.

Start the separate feeder at the start of lay, not in rearing. Feeding high calcium to growing pullets can strain their kidneys, so keep shell out of the rearing house. Most farms switch to layer feed around 16 to 18 weeks, as our point-of-lay pullets guide explains, and the shell feeder goes out with that switch.

Weighing intake: a worked example for 150 hens

You can find out how much shell your hens eat without guessing. Weigh a known amount into the shell feeder on a Monday, leave it out for the week, and weigh what is left the following Monday. The difference is what the flock ate.

Here is the worked example. A farm with 150 hens puts out 4.0 kilograms of oyster shell on Monday morning. The next Monday, 1.6 kilograms is left in the feeder. The hens ate 2.4 kilograms in seven days.

• Total intake: 2,400 grams in seven days.
• Per day for the flock: 2,400 divided by 7, which is about 343 grams.
• Per hen per day: 343 divided by 150, which is about 2.3 grams.

Run that count for three weeks before you change anything. If intake rises sharply for a few days, look for thinner shells, a change in feed or a hot spell, and write it on the record. If intake falls to almost nothing, check that the feeder is clean, dry and in reach, and that the shell has not gone mouldy. Our record keeping guide has a simple sheet you can use for this.

What the shell costs, and what a thin shell costs

Oyster shell is one of the cheapest lines in the feed budget, which is why it gets neglected. Suppose a 50 kilogram bag costs 60 cedis. That is 1.20 cedis a kilogram. At the intake above, the 150-hen flock uses about 2.4 kilograms a week, which costs 2.88 cedis. That is the whole shell bill, every week.

Now compare it with what thin or cracked shells cost you. Suppose the same 150 hens lay 0.8 eggs each a day, which is 840 eggs a week. If 3 eggs in every 100 are lost to cracks, thin shells or breakage, that is about 25 eggs a week. At 50 cedis a crate of 30, each egg is worth about 1.67 cedis, so the loss is about 42 cedis a week.

The bag price in that example is a placeholder, so put your own supplier's price into the sum. The shape of the sum does not change. Shell is cheap, and a flock short of it loses far more than the shell would have cost.

Thin shells: check the rest of the ration first

Extra shell is not a cure for everything. If the flock is laying thin shells, shell in the feeder helps only if the rest of the system lets the hen use it. The shell depends on the whole ration, including phosphorus and vitamin D3, and on a hen that is eating, drinking and not stressed. Our soft-shelled eggs guide covers the causes in detail, so here is the short list of what to check before you blame the calcium.

1. Feed intake: has the flock eaten noticeably less in the last week?
2. Water: were the drinkers empty or hot at midday?
3. Ration: is the feed the right phase for the age of the flock, and has the brand changed?
4. Shell feeder: is the shell still there, dry and clean?
5. Heat: did the shells get thinner during the last hot spell, not just after the last bag?

In Ghana, heat is the most common reason we see shell quality fall suddenly. A hot afternoon cuts intake, and the calcium the hen would have eaten never arrives. The fix is partly feed, partly shade and cooler water, and partly giving the shell a place where birds can reach it in the cooler hours of the day. For the wider picture on lay levers, see our egg production guide.

Harmattan, rains and storing shell

Storage is where the Ghanaian climate bites. In the rains, damp air gets into the shell bag, and a clump that has gone grey or sour will not be eaten. Keep bags off the floor, on pallets or a raised shelf, and keep a lid on the feeder. Use the older bag first, and do not top up a damp feeder with fresh shell on top of a wet layer.

In the harmattan the problem is dust, from the air and from the floor. Dust clings to shell, and a feeder full of dust gets less use. Sweep the shell area before you refill, and wipe the feeder edge so the dust does not drift back in with the next handful.

Keep notes on the weather. A hot week that cuts intake of mash and shell together is a warning about water and shade, not a problem with the shell supplier. Record it beside the intake figure, so next time you can see the link.

Mistakes we see with calcium

These are the errors that come up most often when a farmer says the shells are poor and asks what to do.

• Hand-mixing shell into the mash, so some birds get none and others get a lot.
• Using fine limestone powder as the only source, which gives a short, quick dose and little staying power.
• Putting shell in the broiler house. Broilers do not need extra calcium, and too much can harm growth and leg health.
• Starting shell in the rearing house, weeks before the birds reach lay.
• Letting the feeder run empty on hot afternoons, which is exactly when the birds need it.
• Blaming the shell for thin eggs that are really caused by heat or water problems.

The common thread is that calcium is treated as a bag to pour rather than a supply to manage. A feeder that is checked every day and weighed every week avoids most of these errors.

A weekly routine that keeps shells on track

When buyers ask us what to do with calcium, we give them the routine in this article, because it works on any farm and does not depend on a particular brand. The routine is short, and it takes a few minutes a week.

1. Weigh the shell you put out, and weigh what is left, every Monday.
2. Divide the weekly intake by the number of hens and by seven, to get grams per hen per day.
3. Check that the feeder is dry, covered, in reach, and not empty on any afternoon.
4. Check the shell for damp clumps, dust and smell, and replace it if it looks wrong.
5. Record shell quality for every hundred eggs collected, with cracks, thin shells and breakages noted.
6. Write any heat or water notes beside the intake figure.

Hens that find shell in the same place every day take it reliably. Birds that have to search for it take less, and then the farmer reads the thin shells as a shell problem when the real problem is placement. Keep the feeder where the flock already goes in the afternoon, near the drinkers or the nest boxes, and leave it there.

Starting the layer programme the right way

If you are buying layer chicks from us, the calcium plan starts long before the first egg. The rearing feed should be the right phase for age, and the shell should wait until the birds are close to lay. The point-of-lay switch is the moment to introduce the separate feeder, not a week before, and not a month after.

For the chicks themselves, the batch record and the vaccination timings tell you what the birds have had. Keep that record with your own shell and intake records, so that if laying trouble comes later, you can look back at the whole programme in one place. If you want to start with our layer range, see the layer day-old chicks page, or the breeds overview to compare lines before you choose. When you are ready, use the order form.

Questions farmers ask