[upert]

Could I feed my chickens their ration of calcium with bog standard garden lime? Not the slaked lime or anything like that. It's calcium carbonate after all. See, I can get 25kgs for £4 wheres the stuff I've been buying is that much for about 400 grams.

A friend tells me that chickens would regularly eat the flakes off lime washed cottages.

I mix my calcium in with feed.

[Mum2mj]

You can buy a big bag of oyster shell and grit which is what I give to mine in a separate container which should (I believe) meet their calcium needs along with layers pellets.  It's not very expensive.

[upert]

They have that too. I bought a sack of it for £15. I just want to know why they can't eat calcium carbonate if it's called garden lime tbh.

[New shoot]

Not all limestone is the same.  It varies in the minerals it contains and can cause more harm than good if you are unlucky.  The feed grade stuff has been tested to make sure it will do what you want.

If you feed a balanced layers diet of pellets or mash and have oyster shell available to them, that's more than adequate 

[upert]

Which minerals can cause more harm that good that can be contained in garden lime?

[New shoot]

Magnesium is the main one as it blocks calcium uptake.  Garden lime isn't generally tested for safety as chicken feed, so unless it says OK to feed to chooks, I wouldn't do it - just my opinion and as I've said, I just go the basic pellets and oyster shell route. 

Excess calcium in the diet isn't great for hens.  The 2nd link in here no longer works, but the first one is interesting.   

http://chat.allotment-garden.org/index.php?topic=79429.msg892548#msg892548

[upert]

Calcium oxide might be in there too which can be weaponised.

At least now I have a reason for not sticking garden lime in their feed.

Now, should I feed them gelignite?

[New shoot]

Only if you have a large net to catch the eggs and body armour in case they poop in your direction     

[Rhys]

last time I bought some, I got a big bag of oyster shells. They aren't as fine as the small expensive bags, but the chooks loved them all the same. Mix it with some grit as well. Never had any trouble with brittle shells.