Do Ducks Need Oyster Shell? (how much & how often?)

Over the last 20 years or so, hundreds of ducks have passed through my homestead. I currently keep 5 different flocks and I spend much of my time these days giving duck keeping and breeding talks at clubs and shows around the country.

One question that gets asked time and time again is ‘Do ducks need crushed oyster shells?’.

In this article, I will draw on my experience to explain why ducks need oyster shells and how often they should be fed them.

Yes, ducks do need crushed oyster shells. Laying eggs is very demanding on a duck’s body, and can sometimes lead to a lack of calcium. By adding crushed oyster shells to a duck’s diet, we can replenish some of the calcium a duck may be lacking, helping her produce eggs with strong shells.

Do Ducks Need Oyster Shells?

In the wild, ducks may only lay a couple of clutches of eggs, maybe totaling less than twenty eggs for the entire year.

Many of the domesticated breeds we keep on our homesteads lay far more eggs. Some breeds lay more than 300 eggs per year.

Laying eggs is incredibly taxing on a duck’s body, and she requires a substantial amount of calcium to produce each egg. It is said that each duck egg contains up to 2.2g of calcium.

Even though a good quality duck food will contain some calcium, it is often not enough.

When ducks do not have enough calcium in their diets, they start to lay either soft-shelled eggs or eggs with shells that are so thin they usually break in the nest.

The best way to prevent this problem is to introduce crushed oyster shells into a duck’s diet, either by adding them directly into the duck’s feed or by spreading them around their enclosure and allowing them to pick some up whilst foraging.

Ducks will naturally pick up pieces of oyster shells that have been spread around their enclosure when they are foraging around looking for tasty morsels to eat.

What is the best Oyster shell to use?

The truth is, it does not matter what crushed oyster shell you use, providing it is being sold as suitable for birds (it may say chickens, but it will be fine for ducks too).

For a number of years now I have been using this brand of oyster shell that I order from Amazon.

Ideally, the ingredients should be 100% crushed oyster shells or sea shells. The main thing is that the shells have a high calcium content.

Ducks will also use the bits of shell they consume to help grind up their food in their gizzard. Ducks do not have teeth, so instead they swallow their food down to an internal organ called a gizzard.

In the gizzard, the ducks mix their food with pieces of rock and grit. This breaks the food up and aids digestion.

How to Feed Ducks crushed oyster shells?

There is no real secret to feeding your ducks crushed oyster shells. You essentially have two choices.

You can either mix the grit into the duck’s food, either a little each day, or add a 1lb bag to a 20lb bag of feed. Or, alternatively, you can just scatter a few handfuls of crushed oyster shells around the duck’s enclosure, and allow them to pick them up as and when they want it.

I do know a lot of manufacturers of crushed oyster shells recommend providing your ducks with a separate bowl filled with just crushed oyster shells so the ducks can eat it as and when required, but this method has never really worked for me.

I have always found the ducks just spread the crushed oyster shell all over the floor.

How much Crushed Oyster Shell do ducks need?

I am not aware of a set amount of crushed oyster shell a duck needs on any given day.

Ducks themselves do seem to know when they need it, and they will actively seek it out.

In my experience, the best thing to do is make sure ducks always have access to crushed oyster shells, either mixed into their feed or thrown around their enclosure. That way, they will never run short.

I really do just chuck a few handfuls into each enclosure every few months and leave the ducks to pick it up while foraging for worms and slugs.

Are Grit and Oyster Shells the same?

whilst grit and oyster shells are not exactly the same thing, it can be said that oyster shells do the same job as grit.

Ducks need grit, which is usually an insoluble rock like granite, as part of their digestive system. Ducks do not have teeth, so they can not chew their food to break it down.

Instead, they evolved an organ called a gizzard. The gizzard sits between the duck’s mouth and its stomach. After the duck swallows its food it passes the food into its gizzard where it is mixed with stones and pieces of grit.

The grit’s job is to break down the duck’s food, making it easier for the stomach to digest.

When a duck swallows some crushed oyster shell, it too will end up in the gizzard and the duck will use it along with the pieces of grit to help break down the food. This action also helps break down the crushed oyster shells, making it easier for the duck to absorb the calcium.

So in essence, crushed oyster shell helps the grit break down the food.

On the other hand, grit does not supply the duck with any usable calcium, and so grit can not be used as a substitute for crushed oyster shells.

What age do ducks need crushed oyster shells?

Until ducks start laying, there is no real demand for the extra calcium. Even once they start laying, it will be a few weeks to a few months before the demand for calcium thanks to egg production starts to take a toll on your ducks.

As such, I would not worry about providing your ducks with crushed oyster shells until they are at least 20 to 25 weeks old.

In Conclusion

Laying eggs places a high demand for calcium on a duck’s body. Ducks that are left to lay 200 to 300 eggs a year, without the additional calcium provided by crushed oyster shells, will end up laying soft-shelled eggs or eggs that are easily broken.

Proving crushed oyster shells is as simple as throwing a few handfuls around the duck’s enclosure every couple of months, or adding a small amount to the duck’s feed.

If you found this article helpful, why not check out another one I wrote recently titled ‘Can ducks eat mealworms?’.

Aaron Homewood

Aaron Homewood is‘s poultry editor. Arron has spent over 20 years keeping, breeding, and showing different poultry breeds, including chickens, ducks, geese, and quail.​
Poultry Editor

Article Sources:

  1. Estimation of calcium requirements for optimal productive and reproductive performance, eggshell and tibial quality in egg-type duck breeders