Culling for MG is a difficult decision. It can pass through hatching eggs, but in just a certain percentage. The hen that is raising them can be a carrier for life, so they could be exposed already. I would probably wait and see if anyone shows symptoms over the next couple of weeks. In the meantime, Google MG in chickens, and read at lest the dirst page of articles about the disease. There are good articles from Merck Manual, The Poultry Site, University of FL, and Univ. of Maine. Then you can make a good decision. Many people have MG positive flocks, but they take care to close the flock to new birds or giving away carrier birds. Medicating sick birds with Tylan or oxytetracycline, or culling really sick birds. Fortunately MG does not remain alive in the environment for more than a few days.