That is very interesting regarding the difference between 1 and 2 year old hens. I read through familypendragon's information and there is a good link about how to do what you suggest with treating the eggs. I now plan on doing this in Feb/Mar when I bring in new hatching eggs. Thanks to everyone for the great insights.It is a 10% transfer rate through egg from hens in their first laying season and 2% in hens over 2 years old. So you may not to get it even if the parent stock has it. This is one of the reasons that breeding hens should be over 2 years old. Hatching eggs can also be treated with heat (115 deg for 8 hours prior to incubation) or dipped in an antibiotic solution ( set eggs in warm water for 15 minutes that has tylosin in it) to prevent the transmission to egg. Chicks can also be treated with a strong antibiotic (dengard, tylan 200, etc.) during their first 10 days to prevent the chicks from getting MG. So you can clean up a flock that has had MG (losses are typically 15-20% of the flock so you have survivers/carriers that you can collect eggs from, cull, and then sanitize pens before their offspring are brought back in). All it takes is one chick to get it though and then everyone in the brooder has it so unless you have breeding stock that can not be easily replaces it is probablly easier to just start over again with stock from a MG free flock.