I have a box of left over Bird Gravel w/ charcoal & oyster shells for all types of hard billed birds. According to the box "charcoal" aids in digestive process, "Oyster shells" insure sturdy bone growth.
I have been sprinkle a little of this grits on the chicken feed for my 2 week old chicks for about a week now, and seams to have no ill effects. I would like to know if anybody think this is bad idea.
100 years ago, the poultry scientists considered charcoal nearly essential in the chicken's daily rations.
I believe it was thought important for the same reason that charcoal is often given to dogs - an aid to digestion, as zewei says.
Why charcoal isn't included in modern feed formulas, I have no real idea. Maybe something else takes its place. But, I haven't heard of anything dangerous about chickens being able to eat it by their choice.