It\'s really tough to keep the mycplasma organisms out of a flock entirely. Some folks resolve to live with low grade infections and breed for genetic resistance. As long as the birds receive good care, they should be able to deal with it. The problem comes when multiple infections are at work, such as two kinds of mycoplasma plus a strain of newcastle or laryngo or typhoid, etc. In my opinion the main thing is to avoid prolonged periods of stress, which can be brought on by overcrowding, weather extremes, parasites, etc. Stress can cause the natural immune systems to break down, causing outbreaks of potentially fatal disease combinations.
Keep them dry and out of the wind and avoid overcrowding.