Bone Meal and Limestone in Ghana Poultry Feed

Two sacks side by side, and two different jobs

In most feed stores the two sacks sit close together. One is a fine white powder and the other is grey and gritty, and the seller says either will do for the calcium. Both statements are partly true, and that is why farmers end up with the wrong mineral for the stage they are feeding.

Limestone is calcium carbonate. It is mostly calcium, around 38 to 40 per cent by weight, with no phosphorus to speak of. Steamed bone meal is ground animal bone that has had its fat and most of its organic material removed. It usually carries roughly 24 to 30 per cent calcium and 11 to 14 per cent phosphorus. The bird needs both minerals, but the stage decides how much of each.

When a feed shows a calcium figure, ask where the calcium came from. A mix that gets all its calcium from limestone and none from bone is not wrong, but it is not doing the same job as one that uses bone for the phosphorus as well.

What each bird needs in calcium and phosphorus

These are typical targets, expressed as a share of the whole diet. They describe the ranges that most well-formulated rations use. The specification for your own feed is what counts, and a mill's figures always take priority over a general table.

The shift from broiler to layer is the big one. A broiler starter carries about a quarter of the calcium a peak-lay mash carries. Give a broiler layer-level calcium and the leg problems start within weeks.

Limestone: calcium only, and the grind decides the rest

Limestone does one job, and it does it well. It supplies calcium at a high concentration and at a low price, and it is widely available from quarries. The things to check are purity, sand content and particle size. A limestone that is contaminated with sand, clay or dust costs you the calcium you paid for, plus any trouble the grit causes in the gut.

Fine powder dissolves quickly in the gut, so it gives a short, quick supply of calcium. For a broiler or a pullet, a fine grade in the mash is usually right. For a layer, a fine grade in the mash is only part of the answer. A hen needs a slow supply through the night, when the shell is being formed, and coarse material does that better. Our oyster shell and calcium article covers the layer side in detail, so we will not repeat it here.

Ask the supplier for the calcium percentage and the particle size, and for a sieve analysis if the grade matters to you. Limestone dust is also a respiratory irritant in a dry store, so keep the sacks sealed and wear a mask when you open a fresh bag in the harmattan.

Bone meal: two minerals and a risk to manage

Bone meal is the cheapest source of phosphorus that also brings calcium along. A steamed, defatted bone meal gives 11 to 14 per cent phosphorus, and most of that phosphorus is available to the bird. That is the reason it appears in starter and grower rations in many countries. The product itself is not the risk. The risk is the raw material and the way it was treated.

Bone that has not been heat-treated under pressure can carry bacteria such as Salmonella, and the fat in it turns rancid quickly. The product also varies a great deal. A bone meal that has been steamed properly, dried and defatted is consistent. A bone meal that came from a roadside butcher's pile is not feed, and we would not put it in a bird's mouth. Check the rules that apply to animal by-products in your area as well, because the requirements for feed materials are set nationally.

Ask for a certificate that states the process, the temperature and pressure used, and the testing done. A supplier who can produce it has done the job. A supplier who says "it is all bone" has not.

Why phosphorus is the gap nobody sees

Maize and soya carry plenty of phosphorus, but much of it is tied up in phytate. The bird has limited ability to release it, and its droppings carry a large share through. A ration that looks right on the calcium line can still be short of phosphorus, and the bird shows it in weak bones and poor growth well before the figures would have flagged a problem.

That is why many rations add an extra phosphorus source, and why bone meal is one of the options. Our salt and minerals article covers the other common phosphorus source, and the choice between them comes down to price, purity and how the mix is being used. What matters for this article is the sum, and the sum always has to include phosphorus as well as calcium.

The leg problems that come from a mineral gap are described in our rickets and leg weakness article. Many of the early signs look the same as a calcium excess, which is one reason the figures should be checked before anyone changes the mash.

Worked example: adding phosphorus to a grower mix

Say a grower mix has the right calcium but is 0.1 points short of available phosphorus. You want to add bone meal to close the gap. Take a steamed bone meal with 13 per cent phosphorus, and assume about 90 per cent of that phosphorus is available. That gives 11.7 per cent available phosphorus.

To add 0.1 points, you need 0.1 divided by 0.117, which is about 0.85 per cent of the mix. In 100 kg, that is 0.85 kg of bone meal. That same 0.85 kg brings about 0.23 points of calcium with it, at 27 per cent calcium in the meal.

Here is the step that catches people. If the mix already had its calcium from limestone, the bone meal has just pushed calcium above target. To hold calcium where it was, cut the limestone by about 0.6 per cent of the mix, since 0.23 divided by a limestone at 38 per cent calcium is about 0.6. The adjustment takes two minutes on paper and avoids a flock that gets more calcium than it should. Add the phosphorus, then take the calcium back out.

Worked example: limestone for a layer mash

Take a layer mash with a base calcium of about 0.5 per cent, from its maize and soya, and a target of 3.8 per cent at peak. The gap is 3.3 points. At 38 per cent calcium, limestone has to supply that gap, and 3.3 divided by 0.38 is about 8.7. The limestone share is around 8 to 9 per cent of the mash.

That is a large share, and it shows why the hand-mixing habit is so risky. A mash that goes out at 9 per cent limestone one week and 6 per cent the next has a calcium swing of about a point, which is more than the whole calcium gap you are trying to close. The hens then get a very different shell supply from one week to the next.

Weigh the limestone into each batch, and mix it through the mash in stages rather than sprinkling it on top. Keep a free-choice coarse shell feeder alongside if the mash is limestone-based, so the hens can take extra calcium when they need it.

How much of each to use

These ranges describe typical mixes. They are not a formula, and they should be read against the specification of the feed you are actually using. The top of a range is the most we would put in, and the bottom is often the better choice for a farm that does not weigh its batches carefully.

A farm that does not weigh its batches should stay at the bottom of each range. A farm that weighs everything and tests its minerals can use the middle. Nobody should use the top of a range without a figure in front of them.

Buying limestone and bone meal in Ghana

Limestone comes from quarries, and the quality is only as steady as the quarry. Ask for the calcium percentage and a grain-size description on every batch, and compare the figures between suppliers. Coastal communities also sell oyster shell, which is a different product with a different job. Buy the two separately, and label them when they go into the store.

Bone meal is harder to source well. Look for product from a processor who can show the heat treatment and the testing. Avoid unlabelled bags of "bone powder" from markets and roadside stalls, because nobody can tell you where the bone came from or how it was treated.

A simple check helps on the farm. Put a pinch of limestone into a cup of vinegar. Real limestone fizzes. If the vinegar sits quiet and sand settles to the bottom, you are paying for sand. Keep the sacks dry, since limestone and bone meal both take up damp and cake in a store that is left open in the rains.

Too much calcium does its own damage

Calcium is not free to use, and more of it does not give more bone or shell. Excess calcium in the gut binds phosphorus and some trace minerals, so the bird can end up short of phosphorus even when the feed has plenty on paper. The chick or broiler responds with weak legs, slow growth and a larger number of birds down. The layer responds with eggs that may still be shelled, but with a lower overall output as the bird eats to reach her energy target.

The broiler skeletal problems we describe in our skeletal growth article can come from a calcium excess as well as a shortage. Adding more limestone to a flock that is already lame can make the problem worse. If birds are lame, the first move is a check of the feed spec and a conversation with your vet, not a bag of extra limestone.

Weighing and mixing: where most mistakes start

A kitchen scale is not enough for a batch of 100 kg. You need a platform or hanging scale that reads to within a few grams at the batch size, and it needs to be checked against a known weight every few months. Without it, a scoop of limestone is a guess that changes from one scoop to the next, and a scoop of bone meal is a guess that changes again.

Mix in stages. Put the minerals onto a clean surface, mix them with a small amount of the grain first, then add that blend to the main batch and mix again. A dry, even blend matters more than the speed of the mixer. Our premix and minerals article explains how the same staged mixing applies to the micro-minerals and vitamins.

Wear a dust mask when you handle limestone or bone meal in the harmattan, and wash your hands before you eat. The dust is not dangerous in small amounts, but it is unpleasant, and a clean habit costs nothing.

A checklist before you buy or mix

Use this list each time you buy a new sack of calcium or phosphorus source, and before you mix a new batch.

1. Write down the stage you are feeding and the calcium and phosphorus target from the feed spec.
2. Ask for the analysis of the limestone or bone meal, and file it with the batch number.
3. For bone meal, ask for the heat-treatment certificate. No certificate, no purchase.
4. Do the fizz test on limestone and check for sand settling in the cup.
5. Recalculate the calcium and available phosphorus with the new sources in the mix.
6. If you add bone meal, reduce the limestone by the calcium it brings.
7. Weigh every addition on a scale you have checked.
8. Store the sacks off the floor, sealed, and out of the damp.

The mistakes we see with calcium and phosphorus

These are the errors that cause the most trouble on farms of every size. None of them needs expensive equipment to fix.

• Treating limestone and bone meal as the same product. One gives calcium only, and the other gives phosphorus as well.
• Adding bone meal without taking the calcium back out. The extra calcium makes the mix unbalanced.
• Scooping calcium into the mash. The swing from batch to batch is larger than the gap you are trying to close.
• Using raw or unlabelled bone. The bacteria and the rancid fat are a risk to the flock and to the people handling it.
• Adding more limestone when birds are lame. The cause is often too much calcium, not too little.

Our view, and where to start

We think a well-formulated mill ration handles calcium and phosphorus better than a farm mix built from scratch, and that most farms are better off buying the complete feed for the stage than mixing the minerals themselves. Where a farm does mix, we would use limestone for the calcium, bone meal only from a certified steamed source, and a weighing routine that keeps every batch the same.

If you are starting a flock and want the feed plan worked out alongside the chicks, WhatsApp us on +233 24 915 1503. Our broiler chicks and layer chicks pages list the stages each breed needs. You can place an order through the order form, and the FAQ covers the common questions about starting a flock.

Questions farmers ask