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.

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.

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!

Age

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.

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.

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!

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.

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:

• “What to Expect When You’re Expecting: Backyard Chickens” – the ultimate 101 crash-course in raising chickens
• “Top 18 Backyard Chicken Breeds”
• “Baby Chick Care 101: Brooders, Butts, & Beyond!”
• Caring for Chickens in Cold Winter Weather
• 10 Ways to Keep Chickens Cool During Hot Summer Weather (or Heat Wave)
• When Do Chickens Start Laying Eggs? 5 Telltale Signs it’s Soon

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