Oyster Shell for Chickens: Are They Really Necessary?

Hens need plenty of calcium to lay hard-shelled eggs, and if your hen has a calcium deficiency, giving her oyster shells is an easy way to boost her calcium levels.

A trip to the feed store results in you staring at all of the shelves, wondering if your chickens need any of these things. I wondered if I needed to buy oyster shell for chickens, and if I did, why?

You don’t have to buy oyster shells, but if your chicken has low calcium levels, this is one of the easiest ways to increase this vital nutrient in their bodies. Without proper levels of calcium, you might find soft-shelled eggs, or your chickens might suffer from bone damage easily.

Don’t risk that!

Learning how to identify a calcium deficiency in your chickens is easy, and then provide free-choice access to oyster shells for chickens. Your flock will thank you.

What is Oyster Shell?

As you might imagine, oyster shell is ground up oyster shells; yes – the oysters from the ocean! Sometimes, some commercial oyster shells contain other types of shells, but it’s typically regular oyster shells.

Oyster shells contain high levels of calcium, and some chicken owners refer to this as soluble grit. You might think that feeding your chickens commercial feed will provide all of the calcium that your flock needs, but that’s not always true. Laying hens often need more calcium than what they receive from their daily feed.

Take a good look at the layer feed that you feed to your hens.

If your feed doesn’t provide enough or your chickens show that they need more calcium, feeding oyster shell is a great way to supplement. Did you know that eggs contain 94-97% calcium carbonate, all of which needs to come from your chicken’s body? Chances are your hens don’t receive enough simply from their feed.

An average hen needs 4-5 grams of calcium per day. If you only feed your chickens commercial feed, they’re more than likely okay. If your chickens receive food scraps or free-range, then they’re more likely to have lower levels.

Chickens are all different, so while one hen might find the feed sufficient in calcium, another might. Chicken breeds that lay a lot of eggs often require more calcium than other breeds.

Why Do Chickens Need Oyster Shells?

Something to keep in mind is that not all chickens need to eat oyster shells. Hens who aren’t yet laying have no reason to be fed oyster shell.

Laying hens need oyster shells because they put 20 times the amount of calcium into her eggs than her bones. That’s a lot of calcium that your chickens need for several reasons.

Here are a few reasons that your flock benefits from calcium carbonate.

  • Reduces the risk of eggs breaking
  • Reduces the risk of bones breaking or any bone damage
  • Strengthens blood vessels
  • Protect your chickens’ immune systems
  • improves cardiovascular function

Your laying hens’ diet effects their egg production and the quality of their eggs. It’s the same concept when you’re raising ducks for eggs. Hens give a lot of their nutrients into their eggs, and they’re sensitive to nutritional deficiencies, especially a calcium deficiency.

5 Signs That Your Chickens Need Oyster Shells

How do you know that your hen has a calcium deficiency? Here are a few signs to remember.

  1. Soft Eggshells
    If you find soft, squishy eggshells, it’s the clearest sign that you need to add calcium to your hen’s diet. Eggs only have a hard shell with proper calcium.
  2. Bone Damage
    If your hen suffers from a broken bone or joint injury, it might be due to a calcium deficiency. Hens send all of their calcium to their egg production first before their bones, causing osteoporosis. It also leads to problems standing.
  3. A Sudden Decrease or Stop of Egg Production
    Unless your chicken is at an age when it should stop laying eggs, a lack of calcium might be the problem.
  4. Lameness
    Chickens that are lame or suffer from stiff legs might have bone problems due to low calcium levels. Watch for this in all chickens; it doesn’t just happen to non-laying chickens.
  5. Behavioral Issues
    Having a calcium problem increases the likelihood of poor behavior. If you notice your hen acting meaner or pecking other members of the flock, they might have a calcium problem. Make sure you fix this because an aggressive chicken might injure or kill another flock member.

When to Start Giving Oyster Shells to Your Chickens

Don’t give oyster shells to chickens for no reason; you should only give this when you know that your chickens need additional calcium in their diet. It shouldn’t be given until they’re at 18 weeks old, at the earliest.

There is no need to give oyster shells to:

  • Chicks
  • Pullets not yet laying
  • Older chickens who stopped laying
  • Roosters

So, just to remind you – only give oyster shells to laying hens when you know that they have a calcium deficiency.

What Happens If You Give Too Much Oyster Shell for Chickens

So, what’s the big deal if your chickens end up with too much calcium in their bodies?

Small amounts of extra calcium won’t hurt your flock. The problem becomes when they receive too much, too often.

Your flock might suffer from a few side effects of too much calcium, such as:

  • Kidney failure
  • Inability to absorb calcium
  • Metabolic problems
  • Egg binding
  • Joint issues or injuries
  • Leg abnormalities

How Often Should You Feed Oyster Shells to Chickens

The best way to give oyster shell to chickens is by leaving out a separate bowl of oyster sell; a separate feeder works as well. Giving your chickens free choice access reduces the risk of giving too much to chickens who don’t need the additional calcium.

Chickens might not seem like they’re intelligent, but they understand what nutrients they need. They’ll eat how much they need, and if they don’t need it, chances are the other chickens will stay clear.

Oyster shells should be given year-round, no matter if it’s the winter or summer. It also should be given if you have broody hens or molting chickens.

How Much Oyster Shell to Give to Chickens

There is no set amount of oyster shells to give to chickens. Leave out a feeder or bowl that holds the oyster shells, and give your chickens free choice access.

Never mix the oyster shells into their chicken feed. Doing this risks overloading the chickens who don’t need more calcium with it, leading to potential health problems. It’s safest to let your chickens decide for themselves when they need and want oyster shells.

Oyster Shell vs. Chicken Grit

When you visit your local feed store, you’ll find oyster shell and chicken grit on the same shelf. You might assume that means they’re the same thing or provide the same function.

That assumption is wrong.

Both chick grit and oyster shell are valuable to the health of your birds, but they’re not the same thing. Here’s why.

Chick Grit

The purpose of chick grit is to help your chickens process and digest their food.

Chances are you realize that chickens don’t have teeth to chew up their food. Grit stays in your chicken’s gizzard, and it helps turn food into manageable pieces for their digestive system.

Like oyster shell, grit should be provided using the free choice method. Chickens eat grit when they need it; free-range chickens find all the grit they need in nature, depending on the soil type.

Oyster Shell

Some people call oyster soluble grit, so people become confused. The purpose of oyster shells is to give extra calcium to your laying hens. While it might help with digestion, that’s not the purpose.

6 Alternatives to Oyster Shell for Chickens

Not everyone wants to purchase oyster shell at the store, so there are some alternative options. You need to offer your chickens different choices of high-calcium food to feed your laying hens.

1. Cooked, Ground-Up Eggshells

It might sound morbid or gross, but feeding cooked, ground-up eggshells to your chickens is an easy way to use them up and give your flock extra doses of calcium.

Don’t feed full eggshells to the chickens; they need to be crushed up. Also, getting your chickens in the habit of eating eggs is a bad idea. They aren’t able to determine when they can and cannot eat their eggs. That leads to a problem that you don’t want to have – chickens eating their eggs.

Instead, cook the shells and grind them into a powder. Not only does this decrease any risk of bacteria (a common worry for chicken owners), but it makes it so the chickens can’t recognize that they’re eating eggshells.

One consideration with feeding chickens their eggshells to boost calcium is that if your chickens have a calcium deficiency, their eggs will contain less calcium. If possible, feed them eggshells from other chickens. Also, the calcium releases much slower when using eggshells than oyster shells.

2. High Calcium Feed

Instead of adding something else to their diet that you have to remember, consider using a commercial feed that includes higher calcium amounts. The problem doing this comes when you have a mixed flock with laying hens and hens not yet laying. You want to avoid giving your chickens too much calcium in their diet if they don’t need it.

3. Crushed Limestone

Crushed limestone is what most commercial feeds use as an active ingredient to increase the calcium. It’s possible to buy crushed limestone and add more to their feed.

Be cautious when you buy crushed limestone; dolomitic limestone has high amounts of magnesium, which makes it harder for their bodies to absorb calcium.

4. Table Scraps

Some, not all, table scraps increase your hen’s calcium levels. Feeding these to your chickens benefits the entire flock, so you don’t have to worry about only feeding them to some chickens.

A few table scraps to feed your flock to increase their calcium include:

  • Spinach
  • Kale
  • Yogurt
  • Broccoli
  • Milk
  • Rhubarb
  • Cabbage
  • Salmon
  • Orange Juice
  • Summer Squash

5. DIY Oyster Shell Feed

I don’t suggest going to the store and buying tons of oyster just to make oyster shell feed at home. That won’t be cost-effective. Only do this if you love eating oysters and want to do so to eat them.

Oyster party at home, perhaps?

Some lucky people live in areas with access to large amounts of free oyster shells. That dramatically decreases how much you need to spend to feed your chickens.

You have to prepare the oyster shells properly before feeding them to your flock.

  1. Wash the oyster shells well, and spread them on a baking sheet in a single layer.
  2. Bake the shells at 250 degrees F for 10 minutes. Baking the shells kills any mold spores or other pathogens on the oysters.
  3. After baking, put them in a bag (double or triple lining helps) and start to smash them with a hammer. If you want a powder consistency, put them into your food processor after, but a hammer works well. Plus, it’s fun.

6. Supplements

Nutritional levels work hand-in-hand, so while adding vitamin supplements to your child’s diet won’t fix a calcium deficiency, it provides extra vitamin A, E, and D. These vitamins help your chickens’ bodies absorb more calcium.

Feed stores sell supplements in a powder form, and all you have to do is add a scoop to their water each day. You don’t need to separate your flock; this is safe for all chickens, no matter if they’re laying or not.

Where to Buy Oyster Shell for Chickens

Your local feed store will have several brands of oyster shells available. If you don’t want to leave your house (who can blame you), Amazon has several options for oyster shells.

1. MannaPro Crushed Oyster Shell

The most popular option is by MannaPro. This bag of crushed oyster shells weighs 5lbs, and it’s the most common brand you find in nearly all farm and fleet stores. MannaPro offers pellet-sized, crushed oyster shells that are heat-treated for safety.

Most people pick this option because the price is the best. It’s by far the cheapest option, and if you need to raise chickens on a budget, cost matters!

2. Small Pet Select Oyster Shell

Small Pet Select sells 5 and 10 pound bags of oyster shells. They offered crushed, all-natural oyster shells that are GMO-Free and crushed thinly to help with digestion.

3. Purina Oyster Shell Poultry Supplement

Nearly everyone recognizes the brand Purina; they’re big in the animal world. They sell a 5lb bag of crushed oyster shells for poultry. You should know that these aren’t flakes, but some customers have assumed that they are due to the pictures.


Remember, you should only give oyster shell for chickens when your laying hen that is older than 18 weeks show that she has a calcium deficiency. Your entire flock doesn’t need oyster shells. They should be provided using free choice access all year-round.

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