My girls refuse to eat their grit/oyster shells. To this point, I’ve been trying to sprinkle it in their feed, but I’m afraid they just pick through it. I had a plastic bottle with holes in it, hanging from their coop roof. When they peck it the scratch inside would fall out and they could peck it on the ground. I tried filling that up with grit but they wouldn’t touch it. Everything I try they just ignore it. How can I get them to eat it? (They are free-range most days, but they can’t get enough grit with our soil)