Hi Chickenfan. Grit sits in the crop and mainly the gizzard. It is essential to grind up the food do get the most nutrition out of it. Sometimes calcium material is added (seashells) to assist in egg shell building, but that isn't the reason for needing grit. The grit grinds down as well and is poo'd out in small pieces you wouldn't notice, so that's where it goes. Chickens will pick pieces of stone up, but in fixed runs they rapidly run out, so grit needs to be provided. We sprinkle ours in the feeders. If it goes quickly they need more and if it starts building up we are giving too much. They can manage without it really, but will eat a huge amount of food and digest it badly. So your eggs will become very expensive!