The present invention provides a formulation that prevents virulent MycoplasmagalHsepticum infection in birdsof the order GaIHf ormes. The formulation comprises live MycoplasmagalHsepticum strain K5831 or derivatives thereof in apharmaceutically acceptable carrier. A vaccine that prevents virulentMycoplasma galHsepticum infection in birds of the orderGalliformes is also presented. Methods for administering the formulation andvaccine are also presented.