Mycoplasma gallisepticum vaccination: further studies on egg transmission and egg production.

Leghorn hens vaccinated twice with an inactivated Mycoplasma gallisepticum (MG) bacterin before egg production and subsequently challenged with virulent MG were protected against transmission of MG through the egg. Unvaccinated control hens transmitted MG through the egg at a high rate. When unvaccinated hens were vaccinated with MG bacterin 2 weeks after challenge with MG, there was no significant decrease in egg transmission. Hens vaccinated twice before laying did not suffer as severe egg-production drops as unvaccinated hens did when challenged with virulent MG. In a natural MG outbreak in a leghorn breeder flock, 50 hens were separated from the remainder of the flock and vaccinated with MG bacterin approximately 3 weeks after initial exposure. The unvaccinated hens transmitted MG through the egg at a rate three times higher than the rate of transmission of the vaccinated hens.