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Feeding Chickens Eggshells or Oyster Shells for Essential Calcium & Health

Oh, to be a laying hen and regularly produce eggs… It is a natural but somewhat tedious affair!  Some chickens lay eggs daily, some once per week or less, and some in between. Did you know that eggshells are made up of almost pure calcium? Yup, they sure are – nearly 100% calcium carbonate crystals!

The biological process of forming and laying an egg slightly depletes the hen of her calcium reserves. Without a way to replenish the calcium used, serious and even life-threatening conditions may result! For example, if a hen is not provided adequate free-choice calcium in her diet, and thus cannot properly form eggshells, she may lay soft-shell eggs, become dangerously egg-bound, or even have an egg break inside of her. Those scary scenarios deserve a post of their own (which I plan to write soon!) but for now, let’s focus on proactive prevention.

There are a couple of ways you can provide calcium to your laying chickens to keep them as healthy as possible. Two popular choices are to feed chickens eggshells and/or oyster shells. Let’s discuss those options, along with some best practices and things to avoid.

A diagram of an egg, which says "Anatomy of a Chicken Egg". The shell portion reads: Shell, made up of calcium carbonation, the same material as seashells, chalk, and limestone"
Photo via Egg Truth

Should I offer chickens crushed eggshells or oyster shells?

Wait… Back up. I can feed my chickens eggshells? Isn’t that like, cannibalism or something?  No! It certainly is not. It’s actually very common for chicken keepers to feed crushed eggshells back to their chickens. Furthermore, chickens are known to eat their own eggs and shells out in nature too. We like to mostly offer our girls eggshells – and that is what they happen to prefer as well! I’ll explain why as we go.

Crushed or flaked oyster shells are also available to buy, specifically for this purpose. When we first starting raising chickens, we bought a bag of oyster shells for our girls. Guess what? They wouldn’t touch them. Apparently, the large hard rocks of oyster shells for calcium were completely unappetizing to them. On the other hand, they absolutely love to gobble down crushed eggshells!  I have heard similar stories from many chicken-lady (or man) friends.

To choose oyster shells or egg shells as a calcium supplement is a personal decision – but one that your chickens may help decide for you!

Cost and Supply

Here is the deal: Eggshells are free! Why not make good use of a “waste” product, and not need to spend any money doing so? They seem to be what many chickens prefer to eat anyway. It sounds like a no-brainer, right? However, there is definitely a time and place where using oyster shells instead can come in handy.

One such instance when having oyster shells on hand may be necessary is when you’re running short on eggshells. Say you’re selling eggs, or regularly giving away dozens to friends. In that case, you probably will not have enough spare shells left to supply your flock enough calcium. Egg-laying chickens cannot go more than a few days without that additional calcium source, so you will need to supplement! (Unless you ask your friends to keep the shells and return them to you, which we have totally done.)

Thankfully, we recently found a thinner, flakier, tastier oyster shell than those old “oyster rocks” that our girls disliked so much in the past – one that they will actually eat! Now, we mix these oyster shells with their eggshells to bolster our supply when needed. Even when we aren’t “short”, we add a little oyster shell with their eggshells on occasion, simply to keep them accustomed to eating them.

An image of a pile of crushed flaked oyster shells with a white background.
Flaked oyster shells. Photo courtesy of Amazon

How & When to Provide Chickens Calcium

Whether you’re providing supplemental calcium via eggshells, oyster shells, or both, there are a few important health considerations you need to know about!


First things first. Chickens should not be provided additional calcium until they’ve “come into lay” – that is, have begun to lay eggs, or are damn near ready to. Introducing excess calcium prematurely can actually harm young chickens and cause kidney damage. We generally put out eggshells after one of our young chickens begins to lay, even if the others that are the same age haven’t started yet. You could also begin to offer calcium when your girls start to exhibit the telltale signs that eggs are on the way.

As they mature, chickens need slightly less protein and a bit more calcium. If you pay attention to their labels, you’ll see this reflected in the content of their various stages of feed: chick or “starter”, grower, and layer feeds. Their food is formulated and adjusted accordingly. Thus, laying hens should always be fed a “layer” feed. If you are curious, we feed our chickens this organic layer feed by Scratch and Peck.

Let me decide!

Second, your flocks supplemental calcium source should always be offered as “free choice”. This means that it should NOT be mixed into their food or hidden in treats. Put the crushed eggshells or oyster shells in a separate dish, and keep it stocked and available at all times.

As shown below, we provide shells in a small hanging dish that easily attaches to fencing – with one in the yard, and one in their run. They graze on it as they please. Listening to their bodies, chickens somehow know when they are in need or not! Mixing an excess calcium source into their feed sort of tricks them into eating it, and can lead to “overdose” and health issues similar to if they consume too much too young.

Two chickens, one black and white and one brown and orange, are standing in front of a wire fence. Attached to the wire fence is small metal bowl with hooks, full of crushed eggshells for calcium. Some are spilled on the dirt below too. Succulent plants frame the image in the foreground.
Zoey and Ginger checking out a fresh serving of crushed eggshells. You can see they fling out some, but mostly the oyster shells! Picky picky.

How to Prepare Eggshells for Chickens

Crack an egg, fry it up, and toss the eggshell out in the yard for the birds… right? Not quite! Some folks may do it that way, but we prefer to take a couple extra (but easy!) steps before giving the shells to our chickens. How you choose to prepare your eggshells is ultimately up to you, but let me share how we do it.

Before feeding them back to the chickens, we prefer to bake and crush their eggshells first.

Why bake the eggshells first? Because baking the shells makes them safer for the chickens, by killing any potential bacteria lurking on them with heat. This is especially important if they were sitting around for a while after being cracked open.

Drying the shells in the oven also dries out the membrane, and makes the shells much easier to crush. Finally, it also changes the odor and flavor of the eggs. By doing so, it reduces the likelihood of your chickens associating the shells with the eggs that they lay – and developing a taste for them! It renders them distinct and unrecognizable as eggs. Egg-eating is an obnoxious and difficult habit to break once they start! Trust me… Ugh. Read more about how to prevent and stop egg-eating here.

We love having this reliable autodoor on our chicken coop, which lets the girls in and out of their protected run each morning and night.

Baking, crushing, & storing eggshells

As we use eggs, we save up the shells in a container in the back of the fridge. Keeping them refrigerated reduces bacterial growth, so we don’t bother rinsing them after cracking before storage. Then every month or two, we prepare a large batch. Waiting to bake many at once makes it much less of a hassle or frequent chore!

A close up of a hand holding a plastic tupperware container full of broken eggshells, being saved to bake and feed back to the chickens as calcium.
The container we keep in the fridge, filling it with shells as we consume eggs – until it is overflowing like this! Time to bake a batch.

Spread the shells on a cookie sheet or baking pan. They can get a little stuck and difficult to clean, so we use a cheap pan from a thrift store, dedicated for eggshells. Bake the shells on 300’F for 5 to 10 minutes. We generally do around 5 minutes if they’re already on the dry side, or for a smaller batch, and a bit longer for a large amount or when they’re still quite wet. Remove from the oven, and allow to cool.

Next, crush the shells to a consistency of your hens liking. Some folks grind them up very small, almost into a powder. We’ve found our girls like to peck at slightly larger pieces, about the size of raw oatmeal flakes.

To physically crush the shells, find whatever method works for you. It could be done right on the pan, in a jar, bowl, coffee grinder, food processor… hell, some people even use a mortar and pestle! We typically throw all the baked shells in a designated, re-used, large ziplock bag and then crush the contents with a rolling pin or our hands. A zero-waste, plastic-free option is to do the same in an old pillow case or cloth bag – which is what I plan to try next batch!

Finally, we store the crushed eggshells in jars in the fridge. As needed, we replenish their little dishes outside – so that they’re never without.

A close up of a hand holding a glass pint jar, which is filled with crushed flaky colorful brown and blue eggshells, a source of calcium for chickens.
The final product.

It is as simple as that.

Isn’t it crazy to think that such a small act plays such a significant role in keeping your chickens healthy? Providing a little calcium can save their lives! Literally.

If you’re reading this, I assume that you have (or will soon have) chickens. But if you don’t, you can still save your eggshells! Crush and add them to your compost pile, worm bin, or straight into your garden soil as a natural amendment. The extra calcium is appreciated there too!

I hope you found this post helpful! If you’re interested in more chicken-related articles, you may enjoy:

Please help promote healthy chicken friends by sharing this article!

DeannaCat's signature "Keep on Growing"


  • Jessica Holm

    Another superbly well written article. I was wondering how exactly you crushed your shells — I used to use a mortar and pestle but unless you have a huge one it takes a bunch of batches. I used our meat grinder once but it’s made of plastic and the eggshells actually tore it all up! I will be using a pillowcase and a rolling pin now, thanks so much!

    • Aaron (Mr. DeannaCat)

      Hello Jessica, thank you so much for the kind words! Glad you figured out a process that should work easier for you, thanks for reading and good luck!

  • Brenda Holland

    Thanks so much….While my husband grew up with chickens….I did not. But he was not responsible for taking care of their needs or know what they did or did not need. We started out by putting a few egg shells out for them and then quickly heard no no…they will start to peck at their own eggs before you gather them. So I stopped. Your article was so easy to understand and appreciated very much. I’ll start back again and prep them properly. Again….THANK YOU!

  • Kristen

    Thx so much for this! I didn’t love the idea of spending $$ at a feed store or pet store for Calcium for the girls! Had a scary incident the other night with one of them being egg bound so I wanted to ensure that they are getting more Ca in their diet!

  • thuoc ga da

    every time i come across an article on your post you are so inspiring. This is great work. Keep it up and continue your good deeds. There is a lot am learning from your articles. Thank you!

  • Robin O

    Thanks for sharing your knowledge! Quick question… Is it necessary to store your baked & crushed egg shells in the refrigerator? Or is that just a personal preference? I haven’t stored mine in the fridge before. Wondering if I should start!

    • DeannaCat

      Once they’re baked, it probably doesn’t matter! Sometimes we make a large batch and some of the shells seem a tad gooey still, so we do it just as an extra precaution – but also simply because that is where it seems most convenient to keep the jar of them 🙂

  • Cheryl

    Thank you for all this great information. Love reading your blog and seeing all the pics of your garden. We feed our chooks their baked egg shells too but it is great to actually know all the info about why it is so important for their diet.

    • DeannaCat

      You’re welcome! Yup, it is a big deal – and something that gets overlooked by many chicken keepers. Sounds like you were on the right track anyways! 🙂

  • Megan

    This is great! We use crushed shells as well and will never buy oyster again. We recently have been finding the remnants of eaten eggs in their nesting box. It’s not every day but we will find bits of shell or yolk. I can’t wait to see your next post on this issue!

    • DeannaCat

      Ugh, so frustrating! We are struggling with the same – and I will share my “trick” once I can say it works! Try to stay on top of collecting eggs frequently to reduce their chance to get at them!

      • Stacy

        I read your advice about this early on in our chicken keeping adventures and we’ve never had a problem with the girls eating their own eggs. For a bit, I got kinda lazy and wasn’t doing this and I realized the eggs they were laying had a softer consistency to them. I immediately scolded myself for being selfish and went back to taking care of them properly. Eggs are perfection again! I’m a believer

  • Jory Ryland

    Thanks for this! Our monsters aren’t laying yet, but we’ve been saving shells from my in laws hens. I just made the first batch of eggs. I was really concerned about feeding them shells because I had hens growing up that used to break the eggs. You’ve squashed any doubt I had. Thanks for the blog. Your Instagram and the blog have changed my life!

    • DeannaCat

      I am not familiar with feeds that have “extra” calcium. I know that layer feeds do have oyster shell and calcium added moreso than chick feeds, but I wouldn’t want to trust that alone – even if they claim they’re “oyster rich”. Every chicken expert/resource I have consulted says to keep out separate free choice calcium at all times. So that is my take 🙂

      • melly

        I miss having chickens since we moved.
        Yet another educational, inspiring post.
        Thanks again for sharing your brain with us!

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