ARS | Publication request: Lung pathology and infectious agents in fatal feedlot pneumonias and relationship with mortality, disease onset, and treatments

Submitted to: Journal of Veterinary Diagnostic Investigation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 1, 2009
Publication Date: N/A

Interpretive Summary: Bovine respiratory disease (BRD) commonly results in death losses in beef cattle operations. The goal of this study was to identify the pathogens, observe lesions and record animal treatment data associated with fatal cases of BRD occurring in an Oklahoma feedyard over the course of one year. Six different bacteria and three different viruses were identified. One of the observations from this study was that the length of BRD cases had increased compared to 16-20 years ago. There also appeared to be relationships between different pathogens and severity of lesions. Concurrent infections with multiple pathogens, particularly a virus called bovine viral diarrhea virus, were associated with increased disease severity.

Technical Abstract: This study charted 237 fatal cases of bovine respiratory disease (BRD) observed from May 2002-May 2003 in one Oklahoma feedyard. The data collected included: agent identification, observed pathology, mortality, and animal treatment information. The cattle died either in the sick pen after treatment or suddenly in regular feeding pens without treatment. Postmortem fresh and formalin-fixed lung samples were used for agent identification and histopathology, respectively. Agents isolated were: Mannheimia haemolytica (25.0%), Pasteurella multocida (24.5%), Histophilus somni (10.0%), Arcanobacterium pyogenes (35.0%), Salmonella spp. (0.5%), and Mycoplasma spp. (71.4%). Viruses recovered by cell culture were: BVDV1aNCP (2.7%); BVDV1aCP vaccine strain (1.8%); BVDV1b NCP (2.7%); BVDV2a NCP (3.2%); BVDV2b CP (0.5%); and bovine herpesvirus-1 (BHV-1) (2.3%). There were statistical significant relationships among the agents, lesions, and the animal/treatment data. Based on FDO, treatment interval, and day of death, the clinical illnesses observed in this study were lengthier than those reported 20 years ago. Potentially the treatments currently in use impact the length of illness. There were statistical differences in lesions that correlated with differences observed in animal and treatments. In addition isolation of different BVDV subtypes correlated with differences in lesions and agents identification. This study illustrates the usefulness of BVDV IHC in the identification of PI animals in feedlots, and the potential interaction of PI animals with other infectious agents.