I currently use insoluble crushed granite sold by MannaPro as grit. My confined birds receive a quarter handful every time pens are moved to fresh ground at roughly one week intervals during the winter months. Roughly 1/2 their diet is made up of coarse / intact grains such a corn, oats and millet with balance being a grower / finisher ration. The timing of application coincides with the uptick in consumption of coarse vegetable matter as that I suspect that requires extentive processing by gizzard as well. I have assumed they have more than enough grit with system. How long does the grit last in the gizzard before it is small enought to pass through the rest of the digestive tract? What size is it when it passes?