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Oyster shell for chickens is a calcium supplement for laying hens, offered free choice in its own dish from about 18 to 20 weeks or the first egg. Oregon State Extension says hens on a complete layer feed may still benefit if their shells come out thin or rough, and Alabama Extension says it is cheap and harmless even when it is not needed. This page covers when to start, how to offer it, how it differs from grit and what to do about weak shells. It is part of Kyle’s chicken feeder guides.
Short answer
Free choice, in a separate dishfor laying hens, per Oregon State and Penn State Extension
Start when hens begin laying. Keep layer feed as the main diet, put oyster shell beside it in its own container and let each hen decide. Do not give it to growing pullets, and do not count it as grit.
The short version
- Layer feed already carries about 3 to 4 percent calcium, per Oregon State Extension.
- Oyster shell goes in a separate feeder, free choice, per Oregon State and Penn State.
- Alabama Extension says it is probably unnecessary on a good layer feed but does no harm.
- Thin, easily cracked or sandpaper-rough shells are the sign hens need more calcium.
- Oyster shell is not grit. Oregon State says it is too soft to help the gizzard grind.
Do chickens need oyster shell?
Laying hens need a lot of calcium, but most of it should come from their feed. Oregon State’s feeding bulletin, written by poultry specialist James Hermes, says layer feeds contain about 16 percent protein and 3 to 4 percent calcium so hens lay strong shells without draining the calcium in their bones. It adds that some high-producing hens may need the extra calcium in oyster shell even on a complete feed.
Alabama Extension is more relaxed. It says oyster shell is about 95 percent calcium carbonate, that supplementing a flock on a high-quality complete layer diet is probably unnecessary, and that oyster shell is inexpensive and will not have negative consequences. It also says a hen can put only so much calcium into a shell, so extra calcium beyond her needs does little.
The exception is all-purpose feed. Oregon State says laying hens on an all-purpose or all-flock feed will not get enough calcium for proper shells, so free-choice oyster shell is required. Check the feed tag before deciding.
When should hens start getting oyster shell?
At the point of lay. Oregon State says to start layer feed at about 18 to 20 weeks or when the first egg appears, whichever is first, and mentions oyster shell for laying and breeding hens. Penn State Extension says to give grit and oyster shell free choice, in a separate feeder, to layers over 18 weeks.
Manitoba Agriculture suggests one extra step. It says a pre-lay diet with 2 percent calcium for the two weeks before laying helps young hens build bone reserves, and that the flock should switch to a layer diet of 3.5 percent calcium or more as soon as you see the first egg. Growing pullets on chick or grower feed do not need oyster shell.
How do you feed oyster shell to chickens?
In its own container, free choice. Oregon State says to use a separate feeder so the hen decides if she needs calcium. Manitoba Agriculture suggests a hanging feeder of limestone or oyster shell for birds in floor pens. A small dish or a wall-mounted cup beside the main feeder works, and the best chicken feeder guide covers keeping the main feeder dry and covered.
Particle size matters. Manitoba says to supply a third to half of the calcium as pieces about half a centimeter across, roughly the size of small pebbles, because they stay in the gizzard longer and release calcium at night when the hen is forming the shell. Mississippi State mentions both oyster shell flour and hen-sized oyster shell, and the coarser hen-sized pieces fit Manitoba’s advice.
Don’t mix it into the feed as a routine. Mississippi State Extension describes one exception: for a flock laying thin shells, add 2 pounds of oyster shell to every 100 pounds of complete layer ration as a quick fix, then drop it once shell quality recovers. That works out to 2 percent of the ration.
| Source | When | How | Notes |
|---|---|---|---|
| Oregon State, PNW 477 | Laying hens | Separate feeder, free choice | Required with all-purpose feed |
| Penn State | Layers over 18 weeks | Separate feeder, free choice | Grit offered the same way |
| Alabama Extension | Optional on good layer feed | Not specified | Inexpensive, no harm |
| Manitoba Agriculture | Laying hens | Hanging feeder in floor pens | About 10 percent of the diet as limestone or oyster shell; part as pebble-sized pieces |
| Mississippi State | Only when shells are thin | 2 lb per 100 lb of layer ration | Stop once shells recover |
Sources checked October 24, 2026.
Jill from Ask A Vet Tech says to hold off on grit until chicks are 3 days old, because some chicks gorge on it at 2:09. Her sign of too much calcium is rough, chalky deposits on the outside of the shell or oddly speckled eggs at 4:02. She adds that roosters need only about half the calcium laying hens do at 4:35.
Is oyster shell the same as grit?
No, and the two do different jobs. Oregon State says oyster shell cannot be substituted for grit because it is too soft to aid in grinding. Grit is insoluble stone that lodges in the gizzard and grinds whole grains. Oyster shell dissolves to supply calcium. Manitoba calls insoluble granite grit a poor calcium source, so neither one replaces the other.
Whether hens need grit at all depends on their diet, and the sources split here. Alabama Extension says backyard flocks on commercial feed do not need grit, because the feed is already ground. Oregon State says to provide insoluble grit when you feed scratch grains, unless the birds have access to the ground and can find small stones, and to buy it at a feed store otherwise. Penn State lists grit free choice for layers.
My reading: if your hens eat only layer pellets or crumbles, grit is optional. If you feed scratch, whole grains or let them forage on grass, offer grit in its own dish beside the oyster shell. Oregon State says to limit scratch to what the flock eats in about 20 minutes, about 10 to 15 percent of their daily food.
What causes thin or soft eggshells?
Calcium is the first suspect, but not the only one. Oregon State says thin shells that crack easily, or shells with a rough, sandpaper feel, are the sign hens could use oyster shell. Mississippi State says whole grains or mineral-poor feeds making up the diet are a common cause, and that a complete layer ration as the only feed fixes it.
Manitoba lists the other causes. It says temperatures over 32°C, about 90°F, stress hens and reduce shell strength. Older hens lay weaker shells, and hens that start laying before they get a proper layer diet use up their bone calcium. Too much phosphorus in a homemade feed thins shells. Hens need vitamin D3 in their feed, and Manitoba says the deficiency shows most in winter when birds get little sunlight. It also says to keep hens calm and give them no more than 16 hours of light, so the coop light guide matters here too.
Treats dilute calcium. Alabama Extension says scratch grains, treats or kitchen scraps can hurt laying if hens fill up on them, and that scratch mixed into complete feed dilutes the nutrients. Keep layer feed as the main diet.
When it is not the feed
Manitoba says some diseases, including infectious bronchitis, can cause weak or misshapen shells. If shells stay thin after a week or two on layer feed with oyster shell available, or hens look sick, ask a vet who treats poultry.
Can chickens eat their own eggshells?
The sources disagree. Alabama Extension lists eggshells as another calcium source if you sun-dry them for a day or two or oven-dry them at 350°F for 10 minutes. Manitoba Agriculture calls eggshells a poor calcium source. Oyster shell or feed-grade limestone is the choice both accept.
Questions people ask
When should I start giving my chickens oyster shell?
When they start laying. Oregon State Extension says to switch to layer feed at about 18 to 20 weeks or at the first egg, whichever comes first, and that laying hens may also get ground oyster shell. Penn State Extension says to offer oyster shell free choice to layers over 18 weeks. Growing pullets do not need it.
Do chickens need oyster shell if they eat layer feed?
Usually not much. Alabama Extension says oyster shell is probably unnecessary for hens on a high-quality complete layer feed, but that it is inexpensive and will not hurt them. Oregon State says some high-producing hens may still need the extra calcium, and that thin or rough shells are the sign.
Should I mix oyster shell into the feed?
Offer it in a separate feeder. Oregon State and Penn State both say to feed oyster shell free choice from its own container so each hen takes what she needs. Mississippi State Extension describes mixing 2 pounds into every 100 pounds of layer ration as a short-term fix for thin shells, then stopping once shells recover.
Is oyster shell the same as grit?
No. Oregon State Extension says oyster shell cannot replace grit because it is too soft to help with grinding. Oyster shell supplies calcium, while insoluble grit is small stone that stays in the gizzard. Manitoba Agriculture calls granite grit a poor calcium source.
Do backyard chickens need grit?
That comes down to diet. Alabama Extension says hens on commercial feed, which is already ground, do not need grit. Oregon State says to give insoluble grit when you feed scratch grains, unless the birds can find small stones on the ground, and Penn State lists grit free choice for layers.
Can I feed chickens their own eggshells instead?
Sources disagree. Alabama Extension lists eggshells, sun dried for a day or two or oven dried at 350°F for 10 minutes, as another calcium source. Manitoba Agriculture calls eggshells a poor calcium source. Oyster shell or limestone is the option both sides accept.
Sources
- Oregon State University Extension: How to Feed Your Laying Hens (PNW 477, James Hermes, 2016)
- Penn State Extension: Management Requirements for Laying Flocks
- Alabama Cooperative Extension: Feeding the Laying Hen
- Manitoba Agriculture: Weak Shelled Eggs and Your Small Flock of Laying Hens
- Mississippi State University Extension: Feeds and Nutrition
Written by Kyle
Kyle has kept backyard chickens on his own small farm for five years. He reads the extension research, the spec sheets and the owner complaints, then tells you what he would buy and what he would skip.
