Laboratory investigation of cases of fatal bacterial pneumonia in dairy cows.

OBJECTIVE

Bacterial bronchopneumonia occurs in mature dairy cows but much of the information is extrapolated from knowledge of the disease in calves. The study was prompted by perceptions of an increasing occurrence and a paucity of information on fatal pneumonia in dairy cows in Ontario. The study objectives were to describe the seasonality, main pathogens involved, and suggested predisposing factors for cases of fatal bacterial bronchopneumonia in mature dairy cows submitted for postmortem examination to a diagnostic laboratory, and to evaluate if the frequency of such submissions has increased over time.

ANIMALS

Mature dairy cows.

PROCEDURE

Retrospective study of cases submitted for postmortem examination to a diagnostic laboratory from 2007-2020 that were diagnosed as bacterial bronchopneumonia.

RESULTS

Most of the postmortem cases of bacterial bronchopneumonia in dairy cows were submitted from November to February (54% of cases). was isolated from lung of 61/101 cases. Viruses were only identified in 8/55 cases tested. A minority (29/92) of bacterial isolates had resistance to antimicrobials used to treat pneumonia. Frequently suggested predisposing factors included recent introductions or movement of animals, recent or imminent calving, inclement weather, concurrent diseases, and poor ventilation in barns.

CONCLUSION AND CLINICAL RELEVANCE

This study describes seasonal and annual trends, major pathogens, antimicrobial resistance profiles, and suggested predisposing factors in Ontario dairy cows submitted to a diagnostic laboratory for postmortem investigation of pneumonia and provides insights for understanding why outbreaks occur.