Mannheimia haemolytica in feedlot cattle: prevalence of recovery and associations with antimicrobial use, resistance, and health outcomes

J Vet Intern Med. 2015 Mar-Apr;29(2):705-13. doi: 10.1111/jvim.12547.


Background: Mannheimia haemolytica is an important etiological agent in bovine respiratory disease.

Objectives: Explore risk factors for recovery of susceptible and resistant M. haemolytica in feedlot cattle and explore associations with health outcomes.

Animals: Cattle (n = 5,498) from 4 feedlots sampled at arrival and later in feeding period.

Methods: Susceptibility of M. haemolytica isolates tested for 21 antimicrobials. Records of antimicrobial use and health events analyzed using multivariable regression.

Results: M. haemolytica recovered from 29% of cattle (1,596/5,498), 13.1% at arrival (95% CI, 12.3-14.1%), and 19.8% at second sampling (95% CI, 18.7-20.9%). Nearly half of study cattle received antimicrobial drugs (AMDs) parenterally, mostly as metaphylactic treatment at arrival. Individual parenteral AMD exposures were associated with decreased recovery of M. haemolytica (OR, 0.2; 95% CI, 0.02-1.2), whereas exposure in penmates was associated with increased recovery (OR, 1.5; 95% CI, 1.05-2.2). Most isolates were pan-susceptible (87.8%; 95% CI, 87.0-89.4%). AMD exposures were not associated with resistance to any single drug. Multiply-resistant isolates were rare (5.9%; 95% CI, 5.1-6.9%), but AMD exposures in pen mates were associated with increased odds of recovering multiply-resistant M. haemolytica (OR, 23.9; 95% CI, 8.4-68.3). Cattle positive for M. haemolytica on arrival were more likely to become ill within 10 days (OR, 1.7; 95% CI, 1.1-2.4).

Conclusions and clinical importance: Resistance generally was rare in M. haemolytica. Antimicrobial drug exposures in penmates increased the risk of isolating susceptible and multiply-resistant M. haemolytica, a finding that could be explained by contagious spread.

Keywords: Antibiotic resistance; Pasteurella haemolytica; morbidity; mortality.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Anti-Bacterial Agents / administration & dosage
  • Anti-Bacterial Agents / therapeutic use
  • Cattle
  • Cattle Diseases / drug therapy
  • Cattle Diseases / microbiology*
  • Drug Resistance, Multiple, Bacterial
  • Mannheimia haemolytica / drug effects*
  • Multivariate Analysis
  • Pasteurellaceae Infections / drug therapy
  • Pasteurellaceae Infections / microbiology
  • Pasteurellaceae Infections / veterinary*
  • Risk Factors
  • Seasons


  • Anti-Bacterial Agents