Protective quality of an aluminum hydroxide-absorbed broth bacterin against infectious coryza.

Various aspects of immunity induced by a merthiolate-inactivated, aluminum hydroxide-absorbed chicken meat infusion (CMI) broth bacterin prepared from Haemophilus gallinarium were studied. A bacterin dose of 10-8 colony-forming units (CFU)/ml was the minimal dose which protected a significant number of chickens against intrasinus challenge with live organisms. This finding simplifies production procedures because yields of 10-8 CFU/ml of CMI broth are routinely obtained. A significant number of chickens vaccinated with the bacterin were immune to intrasinus challenge through 9 months postvaccination. On a comparative basis, an egg-yolk bacterin prepared from the same strain protected for only 3 months. Birds vaccinated with broth bacterins prepared from 2 strains of H gallinarum (17756 and M) which shared common surface antigens were immune to intrasinus inoculation with the homologous but not to the heterologous organisms. Preliminary data indicated that the broth bacterin prevented a sharp decrease in egg production when the immunity of vaccinated birds was challenged (instrasinus) at the height of egg production.