I know with AI or exotic Newcastles disease, you don’t have a choice in culling all of your chickens, and that is to save other chickens. But with MG or MS, they may try to lean on you, but I would find out if they can force you legally to cull. Closing the flock with no birds going in or out should be done by anyone who has a contagious disease. Some may choose to cull, while others may try to treat and keep it from spreading. Unfortunately with reportable diseases, though it is good to be able to get testing or a necropsy to find out what a sick bird has, some may fear getting testing.