Comparison of live avirulent PM-1 and CU fowl cholera vaccines in turkeys

The live avirulent PM-1 Pasteurella multocida vaccine, grown in brain-heart infusion broth, was evaluated and compared in two experiments with the Clemson University (CU) vaccine, which had been shown to be effective in preventing fowl cholera in turkeys. Experiment 1 was performed during warm environmental temperatures and Expt. 2 during cooler environmental temperatures. The PM-1 vaccine was comparable with the CU vaccine in protecting turkeys against challenge with virulent P. multocida but was considered no less virulent than the CU because turkeys died after vaccination with both the PM-1 and the CU vaccines. A significantly (P < 0.05) higher percentage of unvaccinated turkeys challenged during the cooler environmental temperatures died than did unvaccinated turkeys challenged during the warmer temperatures. A microtiter agglutination test demonstrated a significant (P < 0.01) correlation between the level of serum anti-P. multocida antibody found 1 wk after vaccination and survival after challenge with virulent P. multocida in Expt. 1 and a significant (P < 0.05) correlation between these parameters in Expt. 2. However, there was a significant (P < 0.01) negative correlation between serum anti-P. multocida antibody titer 1 wk after vaccination and body weight gained 4 wk after vaccination, but before challenge, in Expt. 1, suggesting that vaccination with the live vaccines may have had a negative effect on body weight gain. At 4 wk after challenge or 8 wk after vaccination in Expt. 2, there was also a highly significant (P < 0.001) negative correlation between these parameters in the surviving turkeys.