Mycoplasma gallisepticum causes a slow onset of chronic respiratory disease in chickens and turkeys.  The infection rate is high but the severity and duration of the disease is affected by other factors such as infectious bronchitis, E. coli and stress due to changes in the weather.

In layers and breeders feed intake and egg production are depressed.  In broilers there is a decrease in production.

Mycoplasma gallisepticum can spread by both the vertical and horizontal routes, and indirectly though contaminated equipment, people and infected wild birds.  The disease is more difficult to eliminate in mixed age and free-range flocks.  Eradication is possible with good biosecurity and routine serological monitoring.

Where pullets are raised free of Mycoplasma gallisepticum infection and there is a risk the pullets may become infected during lay, then it is standard to vaccinate the flock at 10 - 12 weeks of age with one dose of MG-Bac.