⠀ Oyster shells for poultry

[Kelly Miller]

I have a question with using oyster shell for extra added calcium for strong egg shells. Since you must have vitamin D for calcium to be absorbed, do any of the products like Purina, or Dumor put vitamin D in with the product, or is it up to me to add it with the oyster shell? I'm not understanding why I hear people using oyster shell and still their hens are producing soft shell eggs. Are we missing something here?

 

[orrpeople]

Oyster shell is always offered "free choice", so it is up to the hen to consume it. That said, production layers often have a problem with over-producing eggs - sometimes two per day - and they simply do not have enough calcium to make two complete shells. The simple solution is to restrict protein consumption, thereby decreasing egg production to a "shellable" number for the hen. Classically, all layer feed has proper levels of vitamin D3 for calcium absorption.

 

[ChickenCanoe]

All chickens need vitamin D so every manufacturer of chicken feed has added vitamin D3.
You can prove this yourself by reading the guaranteed analysis and ingredient tag on every bag of feed. D3 is listed as the 4th or 5th ingredient right after vitamin A.
Other than nutrition, several other things can affect shell quality.
Age of bird, disease, strain of bird, management (high temperature, poor housing), molting and intestinal pH.
While you are correct that it is important for calcium absorption, just as important is the correct ratio of calcium to phosphorus. Specifically, nonphytate phosphorus. Phytate ions have an inhibitory effect on formation of calcium carbonate and therefor, stop egg shell formation.
This ratio is important for layers as well as growing birds. Speaking in overly general terms, growing birds need about a 2:1 ratio for proper skeletal development and actively laying birds need about a 10:1 ratio. Excessive levels of either calcium or phosphorus can inhibit the absorption of the other. You can pump all the calcium you want into a chicken but if there is an imbalance of Ca to P, it can result in soft shells.
Intestinal pH should be slightly acidic. A pH above 6.5 causes phosphorus absorption to nearly cease. High ambient temperatures can cause this because of panting, lowering CO2 in the blood. Other things can influence intestinal pH like high levels of fatty acids and medications like sulfa drugs.
That is the tip of the iceberg, but needless to say that nutrition is a complicated thing. It isn't just about pumping more calcium into them.
One issue complicating matters is feeding of treats. Adding too many things in addition to a complete feed can throw off the proper nutrition contained therein.
Another issue is that it depends on how many eggs are produced. A bird laying 2 or 3 eggs a week doesn't need as much calcium as a bird laying 6 or 7 a week.

That said, in reference to the previous post, chickens don't produce more than an egg a day. 99.99999% of chickens can't and don't produce more frequently than about every 25 hours. After ovulation and travel of the ovum through the infundibulum, magnum and isthmus, the egg spends about 21 hours in the shell gland getting the calcium carbonate application and pigment. There isn't room for 2 eggs at a time in there and ovulation doesn't occur until the previous egg is passed.
Adult hens in production need about 16-17% crude protein, dropping below that number has other complications all it's own.