Efficacy studies on Haemophilus gallinarum bacterin preparations

Broth cultures inactivated and potentiated by selected methods were tested in chickens for efficacy against homologous and heterologous challenge inoculation, using 2 serotype A strains of Haemophilus gallinarum. Although the 2 strains were within the same serotype, they failed to cross protect. One dose of thimerosal-inactivated bacterin was protective against homologous challenge, but 2 doses of formalin-inactivated bacterin were required. A bivalent bacterin protected chickens well against 1 strain, but not the other, at the 1-dose level.