Vaccination of cattle against experimentally induced thromboembolic meningoencephalitis with a Haemophilus somnus bacterin

The capability of a commercial Haemophilus somnus bacterin to protect cattle against experimentally induced thromboembolic meningoencephalitis was examined. Eighteen cattle were vaccinated twice, 8 were vaccinated once, and 14 were nonvaccinated controls. Serum antibody responses to vaccination were measured by gel immunodiffusion, bacterial agglutination test, and complement-fixation test. Deaths occurred in 8 of the 14 controls, 3 of the cattle vaccinated once, and 3 of the cattle vaccinated twice. Two vaccinations were found to give significant protection against challenge exposure (P less than 0.05). There were no cattle which gave positive reactions in the gel immunodiffusion test, and significant changes in bacterial agglutination test titers were not seen in the cattle after vaccination. There was a significant (P less than 0.01) increase in the complement-fixation test titers of cattle vaccinated twice. Serum antibody titers were unrelated to the outcome of challenge infection, regardless of vaccination status, in any of the serotests.