Short answer: Grit helps the gizzard grind food, and oyster shell gives laying hens the calcium for strong eggshells. Birds without grit in the gizzard do not grind feed properly, and hens short of calcium lay soft or thin-shelled eggs. Offer insoluble grit where birds cannot find it for themselves, and offer oyster shell to laying hens in a separate container, never to chicks or broilers.
Key takeaways
- Grit grinds food in the gizzard, and oyster shell supplies calcium for eggshells. They are not interchangeable.
- Free-range birds pick up much of their own grit. Birds kept indoors on mash often need it offered.
- Offer oyster shell to laying hens in a covered hopper and let them take what they need.
- Keep chicks, growers and broilers off oyster shell, since extra calcium is a problem at those ages.
- Use clean, sized grit, and check crops and eggs each week for impaction or weak shells.
Why are my hens eating stones?
Farmers often watch a hen peck at gravel and pull the tin away, thinking it is wasted. A hen with small stones in her gizzard is doing exactly what she should. The trouble starts when farmers treat grit and shell as one product, because they are two different tools with two different jobs.
Grit grinds. Shell builds. If you get the two confused, you end up with a flock that cannot digest its feed properly, or a flock that cannot make strong eggshells, and the cause is often a single missing item in a feed room that looks well stocked.
How a chicken's gizzard grinds food
Chickens have no teeth. Food moves from the crop into the glandular stomach, then into the gizzard, a thick, muscular stomach with a hard inner lining. The gizzard squeezes and grinds, and it needs hard particles to do the work. Those particles are grit.
Without grit, whole grain and coarse feed pass through the gizzard largely unground, and the bird digests less of it. Finely ground mash and pellets need less work, so birds on them need less grit than birds on whole grain. That is the reason the feed form matters when you decide whether to offer grit at all. Our feed formulation basics article covers the particle sizes and feed forms in more detail.
When birds need insoluble grit
Insoluble grit is the stone that passes through the bird and stays in the gizzard. It is most useful in a few specific situations.
- Birds kept indoors on mash or pellets with no soil or gravel to peck at.
- Birds fed whole or cracked grain, which needs more grinding than mash.
- Adult hens on a mixed diet of scraps and grain, where the gizzard has more to process.
- Birds in a house where the litter is wood shavings or husk, which they may pick at without getting much grit from it.
Free-range hens on soil pick up plenty of grit as they forage, and they know how to choose it. Chicks on litter peck at everything, and they sometimes take fine particles from the floor, but you should not count on that as a grit source. If your birds are on a crumble with no soil, offer grit deliberately and watch what they do. Broilers on a set feeding plan, such as the one in our broiler feeding schedule, follow the same logic: the feed form decides the grit need.
Choosing and offering grit
Grit is cheap, but poor grit causes problems that are expensive to fix. Choose a hard, clean stone rather than whatever sand is nearest to hand. Builder's sand and roadside dust can carry dirt, faecal material and contaminants, and they tend to pack into a dirty sludge in a damp tray.
- Source: washed, hard stone grit such as granite or quartz, from a supplier who can say where it came from.
- Size: coarse grit for adults, roughly the size of a grain of rice to a small pea. Use finer grit for young birds that are just starting to take it.
- Offer: in a separate hopper or a shallow tray, kept dry and out of the droppings.
- Quantity: let the birds take what they need, and refill only when the tray is empty or nearly so.
- Check: remove wet, dirty or caked grit each week, and do not top up a tray that is full of droppings.
Grit is not a cure for poor feed. If birds are off their ration, look at the feed first. More grit will not fix a bad mix, and a tray that is always full can lead to birds carrying too much in the gizzard.
Oyster shell: calcium for laying hens
A laying hen puts down a lot of calcium every day in her eggshell, about 4 grams at peak lay. Most of that should come from the ration, but on a standard layer feed calcium can run short during peak lay, and the eggshell is where the shortfall shows first.
Coarse oyster shell is digested slowly. It stays in the gizzard for longer than finely ground limestone, and the hen releases calcium from it as she needs it. That matters because the shell is formed overnight. A hen that has eaten shell during the day has calcium available when she needs it at night. Fine powder passes through quickly and gives a short, sharp hit of calcium, which is less useful for shell formation.
Offer oyster shell free choice in its own hopper, with a lid, and let the hens take what they need. Do not mix it into the mash in large amounts, because a hen that eats too much shell will eat less of her ration.
Who gets what: grit and shell by bird type
This table is a starting point. Your feed supplier and your vet can tell you how your particular ration and house should work, and the feed label will show the calcium level.
| Bird | Insoluble grit | Oyster shell | Notes |
|---|---|---|---|
| Chicks, 0 to 6 weeks | Fine grit only if on whole or coarse feed; ask your vet about the start age | None | Calcium is already set in the starter feed; shell is not needed |
| Growers, 6 to 18 weeks | Small amounts if kept indoors on mash or pellets | None | Extra calcium is harmful to growing birds |
| Laying hens, point of lay onward | Offer, especially on mash or pellets | Free choice in a covered hopper | The most important group for shell |
| Broilers | Litter usually provides enough; offer only if indoors on pellets with nothing to peck at | None | Broilers go to market young, and shell has no job to do |
| Free-range hens | Usually pick up enough from soil | Offer anyway in a hopper | Foraging does not supply reliable calcium. Our guide to kitchen scraps and forage explains what a free-range flock can safely pick up |
For a laying flock, the point of lay is where the shell hopper goes in. Our point of lay pullets guide explains how to move the birds onto layer feed and when to start the shell.
Local shell and limestone: what to buy and what to avoid
Oyster shell from coastal fishing communities is common in the coastal areas of Ghana, and it is cheap when bought in bulk. Limestone from quarries is an alternative, usually sold ground. The particle size is what matters. Limestone ground to powder gets used up quickly and gives less of the slow release that coarse shell gives.
Shell from the seaside arrives with salt, dirt and sometimes sharp edges. Wash it, dry it in the sun, and check it for sharp pieces before you put it in the hopper. Sharp shell can cut the crop and gizzard lining of a bird that swallows it while it is still wet and jagged.
Crushed eggshell can be used as a calcium source for layers, but only once it has been washed and baked. Raw shells from the kitchen can carry salmonella and other bacteria back into the flock. Our article on cheaper poultry feed alternatives covers how to treat eggshell and how much of it is worth using.
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What wrong grit and shell look like
Most grit and shell problems show up in two places: the eggs and the crop. Check both every morning, and keep the notes in your flock record, so a pattern shows up before it becomes a loss.
| What you see | Likely cause | What to do |
|---|---|---|
| Thin, soft or rough-shelled eggs | Calcium short, or shell not available | Offer shell free choice, check the ration calcium, and read our soft-shelled eggs guide |
| Hard, full crop in the morning | Feed too coarse or fibrous, or water short | Check water first, then ask your feed supplier about the grind and the fibre content |
| Birds eating litter, wood or feathers | Boredom, or a ration short of something | Check the ration and the house; offer grit, and call your vet if it continues |
| Chalky droppings and heavy shell intake | Too much calcium | Cut the shell offered and check the layer feed's calcium level |
| Grit scattered and wasted | Open or shallow tray | Use a covered hopper that the birds can work but not scratch out |
| Birds not touching the grit at all | Foraging on soil, or a feed that is already fine | Remove the tray for a week and watch the crops before deciding |
A crop that stays full overnight is a serious sign. Do not wait. Call your vet if a bird's crop is hard, swollen or sour, and do not try to clear it yourself by force.
Mistakes we see with grit and shell
- Raw eggshell from the kitchen. Washed and baked shell is safe. Raw shell is a disease route into the flock.
- Oyster shell mixed into chick starter to be on the safe side. Extra calcium at that age does not help the chick and can cause harm.
- Builder's sand or dusty soil as grit. It is dirty, and it can build up in the gizzard.
- A tin of shell in the corner. A tray left on a damp floor goes mouldy, and hens scratch it across the house.
- A shallow dish of shell in a crowded house. Birds scatter it, and the ones at the back never reach it.
- Switching to pellets and forgetting the grit. The need for grit changes with the feed form, so review it whenever you change the feed.
Most of these come from the same habit, which is leaving grit and shell out and forgetting them. Put them on the weekly checklist, and they stop being a problem.
A weekly grit and shell routine
- Check that the grit tray is clean and dry, and remove any droppings or wet grit.
- Refill the grit only when the tray is nearly empty, not on a fixed schedule.
- Check the shell hopper for damp, mould, rodents and bird droppings, and clean it out.
- Count the hens' eggs and note the shell quality for each day in the record.
- Check the crops of a few birds each morning, looking for hardness, swelling or sourness.
- Check the layer feed label for the calcium level before you buy a new bag.
- Note any change in egg shell quality, feed intake or droppings, and act on it promptly.
If you are starting a layer flock and want birds that are ready for the point of lay, our layer day-old chicks page has the details. Message us on WhatsApp at +233 24 915 1503 with the number of hens you plan to keep, and we can talk through the feed plan with you. You can also place your order through the order form.
Questions farmers ask
Do my hens need grit if they are kept indoors?
Usually, yes, if they are on mash or pellets with nothing to peck at outdoors. Birds on finely ground feed need less grit than birds on whole grain, but they still benefit from some in the gizzard. Offer clean, hard grit in a separate tray, and remove it each week if it gets dirty or wet.
Can I give my chicks oyster shell to strengthen them?
No. Chicks get the calcium and phosphorus they need from their starter feed, and extra calcium at that age can cause problems and does nothing useful for bones or growth. Keep oyster shell away from chicks, growers and broilers, and offer it only to laying hens from the point of lay.
How much oyster shell does a laying hen need?
A laying hen uses about 4 grams of calcium a day at peak lay, and most of it should come from the layer feed. Oyster shell fills the gap, so let the hens take what they need from a covered hopper instead of measuring a fixed amount. Check the calcium on the feed label, and adjust only if egg shells change.
Is sand from the roadside a good grit for chickens?
It is a poor choice. Roadside sand and dusty soil can carry dirt, droppings and contaminants, and wet sand packs into a sludge that the gizzard cannot use well. Buy washed, hard stone grit from a supplier who can say where it came from, and keep it dry in a covered tray.
Can I use crushed eggshell instead of oyster shell?
Yes, for layers and adult birds, provided the shell is washed, baked and crushed into small pieces. Raw shell can carry bacteria back into the flock, so do not skip the baking step. Oyster shell has the advantage of coarse particles that release calcium slowly, so mix them if you can, and check the eggs.
My hens are laying thin shells. Is it the shell or the feed?
It is usually one of three things: not enough calcium in the feed, not enough shell offered, or a problem with the hens' health. Check the shell hopper first, then the feed label for calcium. If shells stay thin after you fix both, talk to your vet about the flock's health before changing anything else.
What happens if a hen eats too much grit?
The grit can build up in the crop or gizzard and cause impaction, especially in birds that are short of water. Watch for hard, full crops and birds that stop eating. Keep grit in a separate tray that is topped up only as needed, and call your vet if a bird looks unwell.
