You can dry or cook or just crush your egg shells and feed your chickens. You only have a problem if they associate the shell with their eggs. The way they do that is by the shape of the egg. If they are crushed there should be no problem with them eating their eggs.
CAN YOU FEED CHICKENS EGG SHELLS???? - Page 5
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This website is really helpful, but if you don't feel like reading it all, I'll summarise.
You should avoid mixing the shell in with the feed in case you have roosters, or hens that no longer lay / haven't started laying, as too much calcium can actually be bad for them. Just but it in a bowl next to the feed and they will eat as much or as little as they need.
Try not to crush it up too small. An eggshell powder will just pass straight through them without them being able to absorb much calcium.
You can leave the bowl out all the time, and they will just take the eggshell as they need it.
The size of the egg shell pieces doesn't really matter, it is the particle size that matters.
Egg shells much like limestone has a small calcium particle size and both pass though a chickens digestive track fast, to fast to fully absorb the amount of calcium they need to produce quality egg shells.
Here's a quote from a study that was done on limestone which has a small calcium particle size like egg shells.
The use of oyster shell resulted in improved calcium retention, and better shell quality as measured by egg specific gravity, and several other criteria such as shell thickness, percent shell, etc. This research was quickly applied in the field, and most breeders' management guides began to recommend various combinations of limestone and oyster shells to achieve optimum shell quality. Since oyster shell is usually much more expensive than limestone, its use is often limited.
I've given mine egg shell. I just let it dry and crush it a little so they don't have huge pieces to fight over. Egg shell is one thing but giving them cooked egg or chicken is a little weird to me. LOL
I introduce a few weeks before I expect them to lay. They normally won't eat it unless they are craving calcium. The younger hens I introduce to the flock will have it available to them as soon as they are with the flock.
What age might that be? I got them March 22nd, they only had the tips of their wings feathered so I'm assuming they were probably less than a week old, they are fully feathered and on grower feed now.