Affiliate disclosure: We earn a commission when you buy through links on this page, including as an Amazon Associate and eBay Partner Network affiliate, at no extra cost to you. We don't invent test results or prices: price tiers ($ to $$$$) are relative, so always check the current listing.
Key takeaways
- Grit is insoluble stone that sits in the gizzard and grinds food. Oyster shell is a soluble calcium source for laying hens. One can't replace the other.
- Birds that eat anything besides complete feed (treats, scraps, forage, grains) need access to grit. Chicks get a smaller chick-size grit.
- Oyster shell is for laying hens. Offer it free choice in a separate dish rather than mixing it into everyone's feed.
- In a mixed flock, separate dishes let each bird take what it needs. Growing chicks shouldn't be fed layer-level calcium, so keep layer products out of the brooder.
- Thin or soft shells can have many causes. Check calcium access first, then talk to a poultry vet or extension office if it continues.
The one-minute version
Grit is small, hard, insoluble stone, usually crushed granite. Chickens don't have teeth. Instead, food passes into the gizzard, a muscular organ that grinds it against the grit stored there. Without grit, whole grains, grass, bugs and kitchen scraps are hard to break down.
Oyster shell is crushed shell that is mostly calcium carbonate. It dissolves in the digestive tract and supplies extra calcium, which laying hens use to build eggshells. Because it dissolves, it doesn't work as grit.
| Grit | Oyster shell | |
|---|---|---|
| What it is | Insoluble stone (often granite) | Soluble calcium carbonate |
| What it does | Grinds food in the gizzard | Supplies calcium for eggshells |
| Who needs it | Any bird eating more than complete feed | Laying hens |
| Chick version? | Yes, chick-size grit | No, keep it out of the brooder |
| How to offer | Free choice in its own dish | Free choice in its own dish |
| Replaces the other? | No | No |
How grit works
A chicken's gizzard holds a small store of stones. When the gizzard contracts, those stones grind food, which is why chickens can eat whole seeds and tough greens. Stones slowly wear down and pass through, so birds keep picking up new ones.
Free-ranging birds find some grit naturally in soil. That doesn't mean they find enough of the right size, especially in winter when the ground is frozen or snow-covered. Feed companies like Nutrena recommend keeping grit available, particularly in winter and snow.
Do chickens on commercial feed need grit?
Complete crumbles and pellets are ground feed that softens and breaks down without much grinding. A bird eating nothing else needs little grit. But almost no backyard flock eats nothing else. Scratch grains, kitchen scraps, weeds, grass and insects all need grinding. If your birds get any of those, offer grit.
Grit sizes
Grit is sold by size to match the bird:
- Chick grit: fine particles for chicks. Manna Pro, for example, recommends offering chick grit free choice in a small dish inside the brooder once chicks eat anything beyond starter.
- Grower or pullet grit: a middle size, sometimes skipped by moving straight to adult grit.
- Adult or layer grit: coarser granite for full-grown birds.
Follow the size guidance on the bag, and switch sizes as your birds grow.
How oyster shell works
An eggshell is mostly calcium carbonate, and a hen in lay needs a lot of calcium to make one shell after another. Most layer feeds already contain added calcium. Some hens need more than their feed provides, especially heavy layers or older hens. Free-choice oyster shell lets each hen top herself up.
Hens are good at taking what they need. Hens in lay will pick at the oyster shell dish, while roosters, molting hens and non-laying birds tend to ignore it. That's the reason to offer it in its own dish rather than stirring it into the feed.
Can I use eggshells instead?
Many keepers dry, bake and crush their own eggshells and offer them like oyster shell. It recycles something you'd throw away. Crush them finely enough that they don't look like whole eggs, so hens aren't encouraged to peck at fresh ones. Oyster shell is still handy as a steady, bagged supply.
Worked examples: which birds get what
Example 1: Six laying hens, layer pellets, some treats
- Grit: yes, free choice, adult size, because of the treats.
- Oyster shell: yes, free choice, in a separate dish.
Example 2: Chicks in the brooder, starter only
- Grit: not strictly needed while they eat only starter. Once you offer any treats, add chick grit.
- Oyster shell: no.
Example 3: Mixed flock with layers, a rooster and young pullets
This is where separate dishes earn their keep. Feed an all-flock or grower ration to everyone and put oyster shell out free choice for the layers. We cover this in layer vs all-flock feed and mixed flock feeding.
- Grit: free choice for all.
- Oyster shell: free choice. Hens in lay will use it, and the rooster and pullets usually leave it alone. If you're unsure, ask your extension office how to handle calcium for your flock.
Example 4: Winter flock on scratch and hay
In winter, frozen ground cuts off natural grit, and many keepers feed more scratch grains. That's when grit matters most. Keep the dish full.
How to set up free-choice grit and oyster shell
- Use two separate containers. A small hanging dish, a wall-mounted cup, or a dual-compartment dispenser all work. Label them, or use different colors, so nobody refills the wrong one.
- Mount them off the floor. Hang or mount dishes at about back height so birds don't scratch bedding into them.
- Keep them dry. Put them under cover. Wet oyster shell clumps, and a covered dish stays cleaner.
- Check weekly. Top up as needed and dump out anything soiled.
- Adjust for age. Switch from chick grit to adult grit as birds grow, and add oyster shell only when hens start to lay.
Signs something is off
- Thin, soft or shell-less eggs: check that oyster shell is available and that layer feed is fresh. Shell problems can also come from age, heat stress, illness or other causes. If it continues, talk to a poultry vet or extension office. Our egg abnormalities guide covers common causes.
- Whole grains in droppings: may point to a grit shortage. Make sure grit is available and the right size.
- A hen not eating or looking unwell: don't assume it's grit or calcium. Contact a vet.
Mistakes to avoid
- Treating oyster shell as grit. It dissolves and can't grind food.
- Mixing oyster shell into all the feed. Non-laying birds then eat calcium they don't need.
- Putting layer feed or oyster shell in the brooder.
- Using builder's sand or random gravel as grit. Use poultry grit sized for your birds.
- Forgetting grit in winter, when birds can't find their own and often get more scratch.
For the bigger feeding picture, see what to feed chickens and winter chicken feed.
Frequently asked questions
What is the difference between grit and oyster shell?
Grit is insoluble stone that stays in the gizzard and grinds food. Oyster shell is soluble calcium that laying hens use to build eggshells. Neither can do the other's job.
Do chickens need grit if they eat layer pellets?
A bird eating only complete feed needs little grit, but most backyard flocks also get treats, scraps, scratch or forage. If yours do, offer grit free choice.
When can chicks have grit?
Once chicks eat anything besides chick starter, offer chick-size grit free choice in a small dish in the brooder. Follow the size guidance on the bag.
Can roosters eat oyster shell?
Roosters usually ignore free-choice oyster shell. Offering it in a separate dish, rather than mixing it into feed, lets layers take what they need while other birds skip it.
Should I mix oyster shell into chicken feed?
It's better to offer it free choice in a separate container. Hens in lay take what they need, and non-laying birds aren't forced to eat extra calcium.
Can I feed my chickens their own eggshells?
Many keepers do. Dry them, bake them if you like, and crush them finely so they don't look like whole eggs. Offer them free choice like oyster shell.