Oyster shell for calcium and mercury

[Tweeza]

I've been thinking alot lately about oyster shells for calcium. I've read here that it's more bioavailable but what about mercury poisoning?

We're growing our own food so we know what's in it but do we really know? Where do these oyster shells come from?

I've read that oyster shell calcium for humans is not bioavailable and a waste of money, so wouldn't that be the same for chickens or are their systems different than ours? You'd think that the chicken's own egg shells would be more bioavailable.

Does some one have study they could point me to?

Thanks for helping me out.

 

[cphilip]

This is a great question. I will only take on part of it. The implied concern about oyster shell that sort of is brought up.

I don't think we have anything to be concerned with there. Now mind you, this is only one study but I have seen a few others that also conclude this

http://docs.google.com/gview?a=v&q=...&gl=us&sig=AFQjCNH5g746m9Y0ezgWdvwYwYM7CzubXQ

I hope you can load that. And you may need to chose the 4 page view to see the tables of results. It is the location of a pdf that is a study of deposits of Mercury and Copper into Oyster Tissue and Shell.

It concludes that Mercury is "BDL" or Below Detectable Level. It does show significant deposits into tissue but not shell. Hopefully this means that we have no reason to be concerned about where our Oyster shell is coming from because these Oysters obviously were exposed to Mercury and Copper and yet the shell was to low to detect for Mercury. I am certain their detectable levels are well below levels of concern.

However note that Copper was detectable in the Shell. However I need to go look at the significance of this. As you know Copper is a necessary element. However it can be toxic in excess and is a marine pollutant. But the levels shown here may just be insignificant and possibly even beneficial.

But great questions I think. Made me look!

 

[cphilip]

Ok... I am finding some references on Copper

"Copper at a level of 800 ppm in a practical turkey diet is toxic but 50 ppm of copper in a purified diet reduces growth. The toxicity of copper is modified by the sulfur acid content of the diet."

Keep in mind we feed Practical Diets not Purified Diets. And also keep in mind we do not feed Oyster shell as the entire diet nor can we assume all the Copper found in Oyster shell might be readily available to the bird either. I imagine only a small percentage of Copper would be taken in by the bird through its Oyster shell supplement.

Now as to its beneficial properties:

"Copper

Copper deficiency in poultry causes an anemia in which the red blood cells are small and low in hemoglobin. Bone deformities can occur. Pigmentation of feathers in New Hampshire and Rhode Island Red chickens is reduced. Copper is required for the activity of the enzyme needed for the cross-linking of lysine in the protein elastin. Dissecting aneurism of the aorta occurs in birds deficient in copper because of the defect in elastin formation. Copper deficiency in turkey poults results in marked cardiac hypertrophy."

Source: Nutrient requirements of poultry
By National Research Council (U.S.). Subcommittee on Poultry Nutrition