Infectious coryza: preventing complicated coryza with Haemophilus gallinarum and Mycoplasma gallisepticum bacterins.

Three types of infectious coryza were produced in unvaccinated chickens by challenge inoculums containing different combinations of Haemophilus gallinarum (HG) and Mycoplasma gallisepticum (MG). Monovalent and combination bacterins of HG and MG were tested to determine their efficacy against chronic complicated infectious coryza. Challenge exposure of vaccinates with MG and HG showed protection against the HG component to be immunotype-specific. Some protection against complicated coryza resulted from HG bacterins only, whereas MG bacterin was ineffective. Protection against transient and chronic coryza was provided by a combination MG-HG bacterin. Two doses of this bacterin gave better protection against upper respiratory clinical signs and lowered the incidence of airsacculitis.