You can buy crushed granite grit at your feed store. Chickens don't have teeth to crush grain and seeds, instead they have a strong internal organ called a gizzard. They ingest coarse sand or fine gravel that goes into this muscle, which uses this material (grit) to grind their food into a digestible paste. Most of us provide this for our birds from the time they are chicks. It is possible, you being in Florida, they get what they need from the sand in your area.when you say grit, what do you mean?