Greetings new guy here. We have 13 grown birds and 3 pullets. Emclosure is 200 ft of poultry fencing in a pasture. They have one good dirt area where they like to scratch and bathe but it's bottomland dirt without any rocks or sand. I occasionally put out oyster/calcium suppliment. Should I provide extra grit? If so would creek sand/rocks be sufficient provided there is lots of small stuff? Thanks in advance for the advice!