My birds always free-range, so I never think about grit. They pick up what they need in the yard. Since our big snow, all the ground has been covered, and will be for a long time. I had to put down some bagged gravel in the path to the coop because of the slippery mess. My hens went wild pecking through it for little bits. I don't know how long they can go without grit in their gizzards, but they acted like they were starved for it! Just wanted to mention this for others who may not be used to supplying it to their flocks. If the ground is covered, they can't get it.