Question about feeding eggshells to chickens?

I'm sure this has been asked before, so I apologize. I have two Brahma hens who have been laying for a couple of months now. They have a pan of oyster shell in their run, but it's low and I need to refill it yet have misplaced the bag of oyster shell. I have wanted to just feed them their own eggshells for awhile now and have some crushed and ready, but I had a couple of questions about doing that.

1) Is it okay to feed just their eggshells, or do I also need to add oyster shell to the mix?

2) On that note, will they every need an oyster shell supplement? I guess I was wondering if eventually the "cycle" of calcium would get weak and they would need calcium from an outside source. These eggshells will have lots of calcium since they've been eating oyster shell, but if they only eat eggshells, will each egg have less calcium in it since it's being cycled through the chicken? Does that make sense?

I may be off base and over-worrying, but I figured I'd find out for sure instead of doing something totally wrong and stupid.

Thanks.

1) yes you can feed eggshells back to them. My experience (and that of others) is that eggshells alone leads to thin shells. I also still use oyster shells, it just works really well.

2) please rephrase, I don't understand your question.

pdirt said:

1) yes you can feed eggshells back to them. My experience (and that of others) is that eggshells alone leads to thin shells. I also still use oyster shells, it just works really well.

2) please rephrase, I don't understand your question.

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I guess you kind of answered my second question with the first answer.

My thought process was that the chicken's body would use the calcium from the oyster shells, both to strengthen their own bones and to make hard shells. So the first round of eggs they produced would have lots of calcium available, and strong shells. But if I took the oyster shell away and fed only their own eggshells back to them, eventually their eggs would have less and less calcium in the shell because it's being constantly recycled and little by little it's being used up by the chicken.

I just didn't know if that was valid or if I'm thinking wrong.

A lot depends on what you are feeding them to start with. Are they getting "layer feed"? or something else? Layer feed has a generous amount of calcium, and is designed to be a complete feed. If they get that, in theory, they don't need oyster or egg shells. Though, it's not a bad idea to provide either item free choice. If they are not getting layer feed as their primary feed (making up at least 90% of their diet) they will definitely need the calcium supplement. Over the full egg laying cycle, you may find that your chooks egg shells are not as strong as they were when they first started laying. That's why chickens naturally take a break from egg laying, to build their calcium reserves. By providing calcium on the side, no matter what the source, you're allowing your girls to self regulate.

Iirc, it doesn't really work that way. I think it's that the calcium is not at absorbable in the egg shells, meaning the chickens can't digest it as well as they can oyster shell. They can get some calcium back from the egg shells, just not as much. Some say that if you have a garden, don't bother feeding the egg shells back to the chickens, but rather put them in your compost...your garden will benefit more than your chickens will.

If I understand correctly, both eggshells and oyster shells are the same form of calcium, which is calcium carbonate (CaCO3).

So there should not be significant difference in absorption.

But since the chickens will also require calcium for their bones and other bodily functions, their calcium will be steadily depleted if their only calcium is their own recycled shells.

The layer feed should certainly have calcium in it, as gardener said.

In any case, it isn't a going to quickly turn into a crisis that you can't find the oyster shells...so clean and crush your eggshells and use them as you suggested. If you notice their new eggs have thinning shells, then you will know that you need to provide supplemental calcium.

There are studies (a search here should find them quickly) that have shown that the reason oyster shell works so well is it stays in the upper digestive tract (where the most calcium absorption sites exist) longer than other calcium supplements.

I agree, your shells aren't going to turn thin overnight. And I was not stating fact, simply my observations. I think it took about 2 weeks before I noticed the thin shells when I only fed back egg shells.

There is a whole lot of Ca in grass (and vegetable scraps), and at least free range chickens have produced good shells long before the commercialization of oyster shells.

The larger pieces of oyster shell acts as a soluble grit in the gizzard, staying there longer, slowly dissolving, as opposed to being passed quickly.

Wow, thanks for all the answers! I guess I'll play with it and see what happens to the eggs.

They are fed a layer feed, and they do seem to eat it. However, they are free range chickens so they eat a wide range of other things as well as veggie scraps we throw them. They've also been known to sneak cat food from the barn cats, though I'm trying to curb that habit and get them to eat more of their layer feed instead.