My 8 week old pullets spend their day in a 100+square foot run with a gravely, dirt floor and have access to an additional 10'X20' dog kennel for several hours a day. I see them picking up dirt/gravel from the run and pecking at it when they are preparing for a dirt bath or sun bathing. Should I offer them additional, store-bought grit or are they fine with what nature provides them? I know I need to offer oyster shells when they're older but what about now?