While most veterinarians agree that Mannheimia haemolytica is definitely a problem pathogen, there are those who disagree about the importance of Pasteurella multocida. Although it may not be as prevalent as M. haemolytica, P. multocida still plays a role in BRD. P. multocida seems to require a much higher challenge “dose” to initiate infection which is likely the reason that calves in confinement housing with inadequate ventilation may be more susceptible to infection and disease from P. multocida. There may also be breed differences in that veterinarians who consult with feedyards that feed a large number of Holstein steers report that the ratio of P. multocida to M. haemolytica identified in cultures is as high as 90:10, and that these P. multocida cases are difficult to treat.

Several other sources have suggested that P. multocida may be a concern.

According to Derek Mosier, DVM, PhD, “In enzootic pneumonia of dairy calves, P. multocida is often the most significant bacterial pathogen, with M. haemolytica involved less frequently.”¹

In another paper published in 2004, by Welsh, et. al., the authors state that a significant increase in P. multocida isolations from beef cattle indicates “an increased prevalence and perhaps importance of P. multocida in shipping fever pneumonia”².

A retrospective evaluation³ of serology from cattle entering feedlots showed that “for individual animals and the herd as a whole,   low levels of antibody to P. multocida, BVDV1a, and BVDV2 were related to decreased net value to owner (carcass value minus total feedlot cost).“ This would suggest that the presence of antibodies to P. multocida in the serum of these calves at arrival may have been beneficial.

Finally, further evidence of the possible significance of P. multocida in feedlots is suggested by prevalence data reported in another paper by Fulton, et. al⁴. Cultures for Pasteurella multocida and Mannheimia haemolytica were reported at nearly the same incidence (25% vs 24.5%).

As to whether or not to vaccinate for P. multocida, that decision will likely vary according to the type of cattle involved, their history, and the veterinarian’s clinical experience with BRD in the past. Currently, vaccines containing both M. haemolytica and P. multocida are priced about the same as those containing only M. haemolytica so there is no additional cost to provide some supplemental resistance to P. multocida. Given the recent information out about P. multocida and its apparently increasing role in BRD, this important pathogen might be worth another look.

References:

1. Vet Clinics Of North America, Food Animal Practice, Vol 12 Number 3, November 1997.
2. Welsh, et al, Journal of Veterinary Diagnostic Investigation, 16:426-431 (2004)
3. The Canadian Journal of Veterinary Research   2002;66:173.180 Evaluation of health status of calves and the impact on feedlot performance: assessment of a retained ownership program for postweaning calves. Robert W. Fulton, B.J. Cook, D.L. Step, Anthony W. Confer, J.T. Saliki, Mark E. Payton, Lurinda J. Burge, R.D. Welsh, K. Shawn Blood
4. Journal of Veterinary Diagnostic Investigation,  2009 Jul;21(4):464-77. Lung pathology and infectious agents in fatal feedlot pneumonias and relationship with mortality, disease onset, and treatments. Fulton RW,  Blood KS,  Panciera RJ,  Payton ME,  Ridpath JF,  Confer AW,  Saliki JT,  Burge LT,  Welsh RD,  Johnson BJ,  Reck A.