A comparative study of Mycoplasma gallisepticum vaccines in young chickens.

Ten-day-old leghorn chickens were vaccinated with the F, ts-11, or 6/85 strain of Mycoplasma gallisepticum (MG) via the intraocular route or subcutaneously with MG bacterin and challenged by aerosol with the R strain of MG at 30, 60, or 90 days post-vaccination. Respiratory reaction post-vaccination, serological response, persistence of the vaccine strain, and protection against aerosol challenge were compared. In general, the ts-11 and 6/85 strains induced a milder post-vaccination reaction than F-strain, produced a weaker serological response, and did not persist as long in the upper respiratory tract. The F-strain-vaccinated chickens had the fewest and mildest air-sac lesions post-challenge, the 6/85 and ts-11 groups had somewhat less protection, and bacterin-vaccinated chickens had no detectable protection against airsacculitis. The F-strain-vaccinated chickens also had the fewest MG organisms in the trachea 10 days postchallenge.