Oyster Shells for Chickens: Benefits, When to Feed, and 6 Great Alternatives

Oyster Shells for Chickens: Benefits, When to Feed, and 6 Great Alternatives

Just like chicken eggshells, oyster shells also have high calcium content. However, it does not necessarily mean you can feed them to your chickens just because you want to. In fact, there are lots of restrictions that you should follow. Otherwise, your chickens may get sick or in worse cases, they may die. To help you understand everything about feeding oyster shells to your chickens, here is the most comprehensive guide you will ever need.

What are Oyster Shells?

This is actually self-explanatory but let’s dig a bit deeper. Oyster shells are the hard exoskeleton (external skeleton) of Class Bivalvia mollusks such as cockles, clams mussels, scallops, and oysters. They contain only about 2 percent of protein but with more than 95 percent of calcium carbonate. And they have many purposes, too!

As compost, the calcium content of oyster shells helps in balancing the pH levels of the soil, improving water penetration, adding nutrients, and strengthening plant cell walls. Oyster shells are also being used in manufacturing concrete blocks, as an additive in transforming plastic to PVC, and as nutritious treats for chickens, particularly hens.


Why Do Your Chickens Need Oyster Shells?

First of all, not all chickens need oyster shells. Roosters, older chickens, and baby chicks don’t need the calcium content from oyster shells. Laying hens are the only ones that need extra calcium because they transfer most of their calcium intake to their eggs. In fact, they give 20 times the calcium content to their eggs than they give to their bones!

By strengthening the eggshells, the calcium from oyster shells then reduces the possibility of broken eggs. Aside from that, it also improves the functions of the cardiovascular system, strengthens blood vessels, and boosts their immune system. Therefore, oyster shells also help in increasing the volume of egg production.


When Should You Feed Chicken Hens With Oyster Shells?

Oyster Shells for Chickens
Oyster Shells for Chickens

Now that you know how oyster shells can help improve your egg production, it does not mean you should feed them to your hens from time to time. Overfeeding your chickens is also bad. Instead, you should understand when they needed them the most. Here are some signs or symptoms that your laying hens are suffering from calcium deficiency:


Eggshell Problems

Closely observe the eggs. If they have thin or soft shells or with no shell at all, it means your hens lack calcium intake. Note that 95% of an eggshell is calcium carbonate.


Your Hens Suddenly Reduce or Stop Laying Eggs

Young hens stop laying eggs or reduce their egg production due to stress, change in weather, overcrowding, and broodiness. Otherwise, they may be lacking in calcium.


Your Hens Become Weak

Hens lose lots of energy while they are laying eggs. So if they are out of balance frequently, having difficulty in walking, or having stiff legs, they probably need more calcium.


Your Hens Have Bone Injury

As mentioned earlier, laying hens transfer only a few amount of calcium to their bones. Therefore, if they have broken bones or could not stand straight, they are most likely to have lost lots of calcium.


How Much Oyster Shells Should You Feed Your Hens?

Crushed Oyster Shells for Chickens Hens
Crushed Oyster Shells for Chickens Hens

There is no standard amount of oyster shells that chickens need. In fact, layer feed has calcium already and your hens only need some extra amounts. This is also why you should give oyster shells separately. Start giving them with only small amounts or little by little. Don’t worry, laying hens are very smart and they will only eat what they need.

As long as you give them oyster shells in moderation, you can give them to your chickens in the entire year even during summer and winter. They also don’t have any negative impact whether your hens go broody or not. On the other hand, the only negative effects of giving oyster shells to them are the instances where they don’t really need them


What are the Negative Effects of Too Much Oyster Shells?

Again, you should give oyster shells only if they need extra calcium or they have a calcium deficiency. Too much calcium is very bad for chickens. But what can happen to them if you give them more than they need? Here are some of them.

  • Egg binding; when hens take a longer time to release eggs
  • Egg problems (same as in calcium deficiency)
  • Metabolic disorders such as abdominal obesity
  • Joint injuries or soft bones (also same as in calcium deficiency)
  • Leg abnormalities such as inability to walk in proportion
  • Kidney damage (Frequent urination and excessive thirst)
  • Can no longer absorb calcium


Oyster Shells vs Chicken Grit: What’s Their Freakin’ Difference?

Sad to say, a lot of beginners in chicken farming are still being confused with chicken grit. In fact, most of them thought that it is the same as oyster shells. This is because both of them are usually on the same shelf in chicken feed stores. So once and for all, let’s understand what chicken grit is and its benefits to your chickens.


What is Chicken Grit Anyway?

Chicken grit is tiny bits of stones that your chickens find in the soil, especially when they are free-range. And yes, chickens eat these stones and they need them for digesting food. The simple reason is that chickens have no teeth to grind food before they swallow it. Therefore, it is the grit that grinds them in the digestive system.

Unfortunately, your chickens might not always find enough grit during free-range. Some soil has less grit, especially the grassy ones. If that’s the case, you must provide it to them. But don’t worry; chicken grit is very cheap and readily available. However, you must know the different types of grits and when you should only buy them.


What are the Two Types of Chicken Grits?

Chicken grits are of two kinds – insoluble and soluble. As the name suggests, insoluble grits (or flint grit) are those that cannot be dissolved in water. This includes sand, gravel, or any mixture of very small stones. Before you buy them, make sure that the sizes fit the age of your chickens. Very small grit might not serve its purpose for some adult chickens.

On the other hand, soluble grits are those that can be dissolved in water. The best example is the oyster shell. They are usually bigger than insoluble grit so you can easily identify them. As mentioned earlier, oyster shells have high calcium content which means only the laying hens need them. They are very dangerous for baby chicks and roosters.


How Does Chicken Grit Work?

As you may know by now, chicken grits serve as your chicken’s teeth while your chickens are eating. Just like us, chickens are omnivores, which means they also eat plants and animals. Once they swallow grit along with the feed, some saliva and enzymes are being added to the food and grit while passing through the esophagus.

Afterward, the mixture will go down to the crop – an expandable compartment in the esophagus. There, the food is being stored temporarily, usually up to 12 hours. Once the food has been initially ground, it will go down to the gizzard, an organ in the chicken’s stomach where the food is being digested further into smaller pieces.

During the process, the insoluble grit and the chicken’s strong muscle movement will grind the food. Then, the food will go to the small intestines which will extract the nutrients from the food. The remaining residue will now become chicken poop. Therefore, food will not be digested properly without the grit, and your chickens will get sick.


Should Baby Chicks be Fed With Grit?

First of all, baby chicks are too young to know the difference between real food and treats. They should be fed with starter feed alone, and therefore, they don’t need grit. This is because such kinds of feed are soft enough and can be digested easily. If you give them grit at this stage, they are likely to experience stomach complications

On the other hand, you should switch them to grower feed once they are between 6 and 20 weeks of age. At this stage, they no longer need the high protein content from the starter feed. And since grower feed is rougher than starter feed, you may now add some grit to help them digest the food. They also need grit if you are feeding them with treats.


How Should You Feed Chickens With Grit?

Again, free-range chickens may find some grit in the soil. But if you think that you need to feed them with grit, give it to them in a separate bowl. They will eat it only if they need it. And again, only your laying hens will need grit that contains high amounts of calcium. Otherwise, your other chickens might suffer from illnesses such as kidney damage.


What are the Great Alternatives for Oyster Shells?

In some cases, you might not want to buy oyster shells and it’s just fine. After all, there are other resources of high calcium that you can feed to your chickens. And sometimes, they are already under your nose but you just don’t realize it. So without further ado, here are some of them.


#1 Chicken Eggshells

As crazy as it seems, chickens eat eggshells, too. As mentioned earlier, chicken eggshells are made of 95% calcium carbonate. However, don’t give them the entire eggshell because it may lead to cannibalism. They might think that it’s alright to eat their eggs. Instead, cook them and crush them into very smaller pieces like powder.

Cooked eggshells reduce the risk of having bacteria. Also, feeding them with eggshells that came from them may not be a good idea, especially that you already know they lack calcium. Instead, choose the shells from eggs that came from the healthier ones. This is also the reason why you should collect eggs in a very organized manner.


#2 Crushed Limestone

Contrary to what some marketers would say, crushed limestone is not considered insoluble grit but rather a great source of calcium. In fact, it is also being as one of the active ingredients in some layer feed. Also, crushed limestone is believed to be having only 33% calcium while oyster shell has 34.3%. But still, the difference is not that big.

By the way, don’t be fooled by some unscrupulous sellers who advised you to use dolomitic limestone instead. Well, it also has high calcium content but with high levels of magnesium, which is usually more than 10 percent. In case you don’t know, excess levels of magnesium reduce the ability of a chicken’s body to absorb calcium


#3 Commercial Feed with High Calcium

Yes, some commercialized layer feed have higher levels of calcium than the others and you can see them on their labels. A laying hen needs about 2 grams of calcium every day before she can make a single egg. But because some of her calcium is being passed on her bones, she will need around 5 grams of calcium every day.

But while a higher-calcium layer feed is also a great alternative for oyster shells, some hens that don’t have calcium deficiency might eat them, too. Again, too much calcium is harmful to those hens that don’t need them. This now becomes a great concern if you have a mixed flock. Make sure you separate the hens that have not laid eggs yet.


#4 Selected Table Scraps

A lot of table scraps (or kitchen scraps) have calcium content, and they are free! In fact, most of them are already under your noses and you just don’t realize it. The best part is that they are suitable not only for laying hens. However, you should know which of them are good for your chickens and which are not. To help you out, here are some of them:

  • Broccoli
  • Cabbage
  • Fresh banana (even banana peels)
  • Kale
  • Milk
  • Orange juice and peels
  • Rhubarb (Stalks only, not leaves)
  • Salmon
  • Spinach
  • Summer Squash
  • Yogurt

On the other hand, here are some table scraps that you should avoid or never give to your chickens.

  • Apple seeds
  • Avocado (especially stone and peels)
  • Citrus
  • Chicken meat
  • Dried or raw beans
  • Onions
  • Potatoes
  • Peanut butter
  • Processed foods
  • Tomatoes
  • Uncooked eggplant


#5 Homemade Oyster Shells

If you love eating oysters and they’re readily available in your area, why not make oyster shell feed by yourself? If you prefer trying this at home, just follow these DIY (Do it yourself) simple steps:

  1. Wash the oyster shells thoroughly.
  2. Spread them on a single layer on a baking sheet.
  3. Bake them at 250 degrees Fahrenheit for about 10 minutes. This is to remove the bacteria and molds. Although they may not be harmful to your chickens, it’s always better to be safe. Aside from that, baking makes them easier to break.
  4. Once the oyster shells cool, place them inside a feed bag or an old pillowcase. Tie it in such a way that no shell will fly away while you are crushing them.
  5. Using a hammer, crush them until they are broken into very small pieces.
  6. If you want them to become powder, use a food processor or blender.


#6 Commercialized Calcium Supplements

Most calcium supplements in chicken feed stores will not fix the calcium deficiency of your chickens. However, they can work together well with feeds because of their nutritional contents. This includes vitamin A, D, and E that can help your chickens absorb the right amount of calcium. And yes, even non-laying chickens can take them.


Where to Find Oyster Shells for Sale?

If you’re looking for oyster shells for sale then we recommend buying them from your local market as it is cheaper than buying them online due to shipping cost. In case that it is not available locally then the best option is to buy it online, you can find it available at a cheap price on amazon and ebay website.



To summarize everything, oyster shells are only for laying hens that have calcium deficiencies. If your hens are healthy, they don’t need them. Also, oyster shells should not be used as insoluble grit because they are soft. In the same manner, don’t use chicken grit as a source of calcium. These two have different purposes and are not interchangeable.


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Breeding Chickens is a free guide to raising and breeding chickens. We cover every topic related to chicken like incubation, taking care of baby chickens, feeding guide, chicken diseases and how to prevent them, designing a chicken house, chicken breeding, and a lot more. We publish an article regularly so please don't forget to subscribe to our mailing list.

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