Transmissibility of the F strain of Mycoplasma gallisepticum in leghorn chickens.

Leghorn pullets free of Mycoplasma gallisepticum (MG) were infected with the F strain of MG at approximately 18 weeks of age. At various times up to 27 weeks postinfection, infected chickens were placed in a pen with uninfected controls. Infected chickens remained tracheal carriers up to 49 weeks postinfection. Infection was readily transmitted to penmates during the first 4 weeks postinfection; in most instances from 6 through 27 weeks postinfection, transmission to penmates became progressively slower. Five groups of broiler chickens were reared in the same house as the Leghorn chickens up to 8 weeks of age. Only one of the 5 groups became infected. Birds in this group were reared in a pen adjacent to infected pullets from 1 day of age and were apparently not infected until they were nearly 8 weeks old. At no time did transmission occur between groups separated by an aisle or empty pen.