Complement fixation titers in cattle following intranasal inoculation of Hemophilus somnus

Five bulls were inoculated intranasally with a live culture of Hemophilus somnus originally isolated from a clinical case of Hemophilus septicemia. Preinoculation and postinoculation blood samples were taken at weekly intervals for nine weeks for measuring complement fixation titers and daily postinoculation temperatures were taken for one week. Three animals had transient fever and slight lethargy was observed in two animals had a transitory rise in complement fixation titers in the second to fifth weeks postexposure while one animal which had been seronegative on preinoculation testing produced little serological response to the organism. The experiment demonstrated that the nasal instillation of young cattle using an originally pathogenic H. somnus isolate is capable of stimulating only transitory complement fixation antibody titer.