Grit is not added to feed - any feed. Maybe you're thinking calcium? But that wouldn't be in starter either, as extra calcium is only meant for laying hens, hence it's in layer feed not starter. It's very dangerous to add grit to feed, if the chickens eat too much it can clog them up and kill them. Grit is not soluble or digestible and will quickly add up if they eat it regularly. It's worn down inside the gizzard very slowly as they digest their food, so they only need to replenish it very infrequently. The chickens know when their gizzards are running low on grit and need to eat more, they are very good at self regulating. So grit should always be offered separately from any of the food.
