Evaluation of Pasteurella multocida mutants of low virulence. II. Immunologic response of turkeys.

Vaccination of turkeys by administering Pasteurella multocida mutant PM#1 or PM#3, either by the oculo-nasal-oral method or in the drinking water, induced a level of protection comparable to vaccination with the Clemson University (CU) strain or the M-9 vaccine. The level of protection was not altered when PM#1, PM#3, or the CU strain was grown in brain-heart infusion (BHI) broth or BHI agar. Under extemely severe challenges, the CU strain provided a greater level of protection than PM#1, PM#3, or the M-9 vaccine. It also was apparent from this study that the less-virulent mutant organisms and the M-9 vaccine require a higher concentration of organism per vaccine dose than the CU strain to provide similar protection.