Feeding Oyster Shell to Backyard Chickens

If you have laying hens, you probably have already done a ton of research about the food, housing, and other requirements that your chickens need to stay healthy.

But have you thought at all about oyster shell?

Oyster shell is an important component of a laying hen’s diet that should always be offered to your birds free choice.


What is Oyster Shell?

Just as the name suggests, oyster shell is simply the ground up shells of oysters.

In some cases, commercial oyster shell may contain other types of shell, but usually it’s just plain old oyster.

Oyster shell is high in calcium and is also referred to as soluble grit.

Many feed companies will tell you that commercial feed is enough to support the needs of your chickens.

While this is probably true if you are raising broiler birds, if you’re raising laying hens it’s probably not something you want to risk finding out on your own.

Some layer feeds simply don’t contain enough calcium for your hens, and you’ll need to see how your individual birds respond until you know for sure.

Why risk it? Feed oyster shell. An egg contains 94-97 percent calcium carbonate, all of which must be pulled from your chickens’ bodies.

If you have chickens that lay frequently, as in everyday or every other day, they will need even more oyster shell than those that lay just a couple of times per week.

We recommend Manna Pro Oyster Shell.

Manna Pro Oyster Shell, 5-Pounds
  • Pellet size crushed oyster shell
  • Great source of calcium
  • Builds strong eggshells

Why Do My Chickens Need Oyster Shell?

chicken oyster feed
Øyvind Holmstad [CC BY-SA 4.0]

While most chickens will benefit from being fed oyster shell, keep in mind that not all will need it.

Hens who are not yet laying, for example, probably don’t need to be fed oyster shell.

In just a single year, a hen will put twenty times the amount of calcium into her eggs that is found in her own bones.

That’s a lot of calcium!

That being said, laying hens will benefit in the following ways:

  • Added calcium that reduces the risk of egg breakage
  • Reduced risk of bone damage
  • Strengthens blood vessels
  • Protects and strengthens your chickens’ immune systems
  • Improves cardiovascular functioning

As with other egg-producing species, even mammals, diet strongly influences egg production.

A hen is even more sensitive to nutritional deficits than most other species. For her to make strong eggshells, she must have access to plenty of calcium.


What are Some Alternatives to Store Bought Oyster Shell?

If you don’t want to purchase commercial oyster shell, there are several alternative choices of high-calcium foods you can feed your laying hens.

1. Ground Up, Cooked Eggshells

It may sound gruesome, but feeding eggshells back to chickens is a great way to recycle old shells and to provide your girls with a good source of calcium.

Avoid feeding full eggshells to your chickens, as this will confuse them into eating their own eggs – this is a habit you definitely don’t want your chickens to get into, as it’s exceptionally hard to break.

Some people fear that feeding eggshells back to chickens can lead to bacterial infections.

If you cook your shells down before grinding them into a powder, you shouldn’t need to worry about any bacteria infecting your chickens.

Cooking the shells also helps to make them less recognizable so that your chickens don’t try to eat them.

One caveat to keep in mind is that if your chickens’ diet is already low in calcium, they aren’t as likely to have high quantities of calcium in their own eggs.

Therefore, you may need to feed your hens the eggshells of other birds in order to get her back into fighting shape.

Another small problem with feeding egg shells to chickens as an alternative to oyster shells is that eggshells don’t contain the same fast-release source of calcium as oyster shell.

They are still beneficial and a good source of calcium, but you need to be much more consistent in feeding them if this is your calcium source of choice.

2. High Calcium Feed

Some layer feeds have enough calcium in them to provide appropriate quantities for your chickens.

There are also commercial feeds that are higher in calcium to meet this need specifically.

However, if you have a mixed flock of chickens (one that contains laying and non-laying chickens), it’s recommended that you avoid feeding this kind of food to prevent excess calcium.

Look for a layer feed that has at least sixteen percent protein and larger amounts of calcium.

These can be fed when your hens are about eighteen weeks old or whenever the first egg is laid, whichever might happen first.

But remember – don’t feed layer feed to birds that don’t need it.

3. Crushed limestone

This is the type of calcium most commonly found in commercial laying feeds, but you can also purchase it on its own.

Be careful in the type of limestone you feed, however, as dolomitic limestone contains larger amounts of magnesium and can interfere with calcium absorption.

4. DIY Oyster Shell Feed

While feed stores sell bags of ground oyster shells for a relatively low price, you may decide that you want to make your own oyster shell supplement.

This isn’t financially feasible in most cases – buying oysters just to make oyster shell feed is definitely not worth it (unless you really love eating oysters, that is!). 

However, if you have access to a large amount of free oyster shells, then this is a great way to cut down on your overall feed bill.

Check with your local restaurant to see what they do with their old oyster shells.

Usually, they just throw them away.

If they’re willing to save them for you, you might be able to get out of this at no extra cost to you.

To prepare the feed for your chickens, start by baking the shells at 250 degrees Fahrenheit for about 10 minutes.

You can do this on a baking sheet. Baking the shells will kill off any mold or other pathogens on the shell and also make them easier to crack and to work with.

Once you’ve baked the shells, put them in a bag. Smash the bag with a hammer or even drive over it with your car to crush the shells down into small pieces.

This won’t take long at all. If you want a powderier supplement, you can then put the shells in your food processor. That’s all there is to it!

5. Table Scraps

There are some common household foods that can help boost your hen’s calcium intake.

The benefit of feeding scraps is that all of your chickens will benefit from them – not just the layers – providing for a more well-rounded, easily digested treat.

Here are some high-calcium options:

  • Spinach
  • Swiss chard
  • Mustard greens
  • Kale
  • Yogurt
  • Dandelion greens
  • Red clover
  • Broccoli
  • Brussels sprouts
  • Cheese
  • Milk
  • Basil
  • Rhubarb
  • Cooked beans
  • Cabbage
  • Summer squash
  • Garlic
  • Orange juice
  • Shellfish
  • Salmon and sardines

6. Vitamin Supplements

This won’t necessarily provide your chickens with any more calcium and should not be viewed as a stand-alone solution to calcium deficiency.

However, providing your chickens with additional quantities of vitamin A, E, and D can improve their absorption of calcium more so than if they were just eating the calcium by itself.

These supplements can be purchased in a powder form and should be added to their water every other day.

They won’t hurt non-laying birds, either, so you don’t have to worry about providing separate watering systems for roosters or young chickens.


What are the Signs That My Chickens Need More Calcium?

If you’re new to raising chickens, you might think that your hens can get by on the feed you buy at the local feed store.

While this is often true, your chickens might need additional calcium if you’ve noticed any of the following problems.

  • Soft eggshells: If the shells of your chickens’ eggs are soft, squishy, or simply nonexistent, it’s time to add calcium. For a hen to lay an egg with a hard shell, she needs a diet that is high in calcium.
  • Bone damage: Have you had a hen suffer a broken bone or a joint injury in the last few weeks? If so, it could be due to a lack of calcium. If a hen doesn’t have enough calcium while she is making an eggshell, she will steal it from the calcium stored inside her bones. This can cause osteoporosis and give her trouble standing.
  • Drop in egg production or failure of hens to start laying: Have your hens surpassed the age at which they should be laying eggs? Or did they stop laying (or slow down) altogether? If so, a lack of calcium could be to blame.
  • Lameness: Chickens who are lame or seem to have stiff legs may not have bone damage as a result of too little calcium. However, these early signs can present as signs of calcium deficiency even in non-laying chickens.
  • Behavioral problems: Chickens who are low on calcium are more likely to engage in pecking and increased overall activity. This can cause injury and even death in certain members of your flock.

How Often Should I Feed My Chickens Oyster Shell?

Leave out a bowl or detached feeder of oyster shell so that your laying hens have free choice access to it.

While you can sprinkle oyster shell into the feed, you risk chickens who don’t need oyster shell consuming too much calcium.

Instead, allowing the birds to self-regulate their calcium intake is the best bet.

Fill a bowl full of oyster shell and place it alongside your chickens’ feed. Your hens will figure out how much they need to eat, and when.

Simply refill it when it is empty. The average hen will eat about 100 grams of feed with 4 percent total calcium per day.

You should feed oyster shell consistently around the year, no matter the season or weather.

Even if your hens stop laying while they are molting, broody, or taking a break during the winter, you should continue offering oyster shell.

It will help to strengthen their bones and make it possible for them to lay stronger, more numerous eggs later in the season.

It takes ninety minutes for food to pass through a chicken’s digestive tract.

When your hen is wake and eating, the calcium will dissolve into her bloodstream quickly.

It takes a hen roughly 25 hours to create an egg (there is some variation here among breeds).

Therefore, she should have consistent access to calcium to make sure her body is always ready to produce a hard shell.


What is the Nutritional Value of Oyster Shell?

Oyster shell is high in calcium, which is what your chickens need to lay healthy eggs.

Hens who have low levels of calcium are more likely to lay soft- or no-shelled eggs, as well as to suffer from broken bones in the legs and feet in particular.

Eggshells, as previously mentioned, are almost entirely calcium carbonate.

Almost all the calcium that is needed to produce a healthy eggshell must come from a hen’s diet.

She should be consuming roughly four grams of calcium per day to get the two grams of calcium needed to make one eggshell.

The larger your hen, the more calcium she will need.

When your hens eat oyster shell, their bodies break down into separate calcium and carbonate components in the intestine of the hen.

They will then be absorbed into the bloodstream and transmitted to the shell gland, with any leftover stored in the bones of the bird.

Hens actually have unique bones called medullary bones that store calcium, helping to make them stronger and more stable.


Should I Feed Oyster Shell to Chickens That Aren’t Laying Yet?

While it generally won’t hurt them, you don’t need to worry about feeding oyster shell to the following types of chickens:

  • Chicks
  • Pullets that aren’t yet laying
  • Older chickens who have stopped laying
  • Roosters

If you are raising a mixed flock of birds, keep your oyster shell separate so that the birds who need it can access it.

This will prevent overfeeding oyster shell to the birds who do not need it. While small amounts of extra calcium won’t hurt these chickens, too much can be detrimental.

Here are some of the potential side effects of too much calcium:

  • Kidney failure
  • Inability to absorb calcium over time (as a result of an overloaded system)
  • Leg abnormalities
  • Metabolic issues
  • Difficulty with vitamin D and phosphorus absorption
  • Egg binding
  • Joint problems

Do not start feeding your hens oyster shell until they are at least 18 weeks old. Oyster shells are only meant for hens who are laying eggs.

Remember, your hens will only eat as much calcium as they need, but if you mix calcium into hens’ food and they aren’t ready for it, it can cause severe kidney damage.


What is the Difference Between Oyster Shell and Grit?

Many people (incorrectly) assume that oyster shell and grit are the same, and will produce similar effects in their backyard flocks of chickens.

While both are vital to the health of your birds, they are not the same. Without either, serious health conditions can arise, affecting your flock’s output and overall wellbeing.

About Grit

Grit helps your chickens process their food.

Since chickens don’t have teeth, they need a way to reduce the particle size of their food down to something that is smaller and more manageable.

Grit helps them to do this.

When your chickens consume grit, it passes down to the gizzard. It stays there for some time, waiting until it has worn down enough to safely pass through the chicken’s digestive system.

While it’s there, it helps grind food down into paste.

The digestive system of your chicken will then absorb all the water and nutrients it needs before eliminating it.

Grit helps turn food into something that is more easily digested – and used – by the body of your chicken.

If your chickens don’t have access to grit, in either a supplemented or natural format, they will have a hard time digesting food.

Grit can be purchased at the feed store. It’s essentially just chipped flint or granite. It’s inexpensive and does not expire.

Grit should be provided free choice. Many chickens will get all the grit they need if they are free-ranging, but this will depend on your soil type as well as how much access to open space you give them.

Oyster Shell

Where people tend to confuse oyster shell and grit is that oyster shell is often referred to as soluble grit.

It dissolves quickly in the hen’s digestive system and is stored to be used later in making eggshells and supporting the overall health of your birds. While grit is insoluble, oyster shell dissolves in the gut.

Although it can help with digestion, that’s not its overall purpose – it’s meant solely to add calcium to the diet of your laying hens.

The bottom line? While you need to feed your chickens both oyster shell and grit, the two serve very distinct (yet vital) functions in your chickens’ health and wellbeing.


Why Oyster Shell is Important

If you’re thinking, “Yeah, yeah, enough already. We get it. My chickens need more calcium,” you’re right.

They do!

But the fact of the matter is that a lack of calcium doesn’t just affect your chickens – it also affects you directly.

If you keep laying hens, you undoubtedly do so because you want to consume (or sell) the eggs.

An eggshell is the best way to prevent bacteria from sneaking inside an egg.

A strong eggshell will be much more likely to withstand outside pressures, while a weak one can carry dangerous diseases.

That’s likely not something you want to be thinking about over breakfast!

Instead, the next time you’re out in your chicken coop, consider laying down a pan of oyster shell. Your hens will thank you for it!

Last update on 2020-10-29 / Affiliate links / Images from Amazon Product Advertising API