(Disclaimer - There are varying opinions on the statements concerning culling flocks for MG/MS. Many state Agricultural Department veterinarians DO NOT suggest culling a flock as these diseases are currently very prevalent... up to 75% of ALL domestic flocks *may* already be carriers of MG/MS.)
Recently an acquaintance of mine (who for privacy reasons we will call “X”) lost his/her entire flock of rare breed chickens to mycoplasma gallisepticum (MG). Due to the number of birds X had as well as the breeds involved, X’s monetary loss would be well into the thousands, though if you were to ask X I believe s/he would tell you that the emotional toll was far greater.