In young cattle, bovine respiratory disease (BRD) is a major cause of death and Mannheimia haemolytica is a frequent pathogen. Knowledge of fatal BRD in adult cattle is more limited. We assessed the importance of infectious BRD as a cause of death in adult cattle and determined the associated pathogens. We analyzed data from 737 adult cattle necropsies at the Pathology Unit for Large Animals at Oniris, Nantes, France over a 6 year period (2013–2019). Each carcass was subjected to a complete necropsy. Lungs showing macroscopic lesions were classified into three categories: infectious primary pulmonary (IPP) lesions, thromboembolic pneumonia (TEP) and others (aspiration pneumonia, verminous pneumonia, and local extension of an extra-pulmonary inflammatory process). Half of the lungs with IPP macroscopic lesions were sampled for histology and submitted for polymerase chain reaction. BRD was the second leading cause of death (15.7%) after digestive diseases (32.2%). A strong predominance of IPP lesions (42.3%) and TEP lesions (39.6%) was also demonstrated. In IPP macroscopic lesions, fibrinous, hemorrhagic and/or hecrotic (FHN) bronchopneumonia accounted for 77.6% of macroscopic lesions. Mannheimia haemolytica was significantly associated with FHN bronchopneumonia macroscopic lesions. This study suggests that Mannheimia haemolytica should be included in the differential diagnosis of BRD in adult cattle.

Bovine Respiratory Disease (BRD) is a leading cause of morbidity and mortality in young cattle upon feedlot arrival. The immune response plays a dual role in infection control and lung tissue damage, but few studies have assessed cytokine levels during natural BRD outbreaks. Advances in multiplexed assays now allow for broader cytokine and chemokine profiling in cattle. In this nested case–control study, 184 young bulls from nine French fattening farms were clinically assessed and underwent thoracic ultrasonography (TUS) weekly during the first month on feed. BRD cases (n = 98) and matched healthy controls (n = 86) were selected based on clinical signs. Fifteen cytokines and chemokines were quantified in plasma using a bovine-specific bead-based multiplex assay, on the day an animal was first detected as sick and in its matched control sampled on the same day. BRD-associated pathogens were assessed using qPCR on nasal swabs and paired serology. The link between cytokines and clinical, microbiological, and preconditioning (vaccination and preventive antibiotic treatment) variables was investigated using the Wilcoxon-Mann–Whitney test, mixed-effects linear regression models, and multivariate clustering. Cytokine and chemokine levels did not distinguish clinically sick from healthy animals. No specific cytokine profile was associated with infection by a given pathogen. However, IL-17A and IFN-γ concentrations were positively associated with treatment relapse and disease severity, suggesting that they may have prognostic potential. Cluster analysis revealed three subgroups with distinct cytokine patterns and health outcomes, in association with preconditioning variables, highlighting the critical role of these interventions in shaping the immune response during BRD outbreaks. This study is the first to report the measurement of such a wide range of cytokines during spontaneous BRD episodes in young bulls. While not diagnostic when considered individually, cytokine profiles may hold prognostic value and could be integrated into multimodal risk stratification tools, in combination with clinical, microbiological data, and TUS results, to improve BRD management in the field. Preconditioning practices, such as vaccination or preventive antibiotic administration, significantly influence early immune responses and should further be investigated to refine prevention strategies and individualize health monitoring protocols at feedlot entry.

Background: Thoracic ultrasonography (TUS) could improve antibiotic treatment selection in cattle with respiratory diseases. Hypothesis/Objectives: Evaluate the association between respiratory pathogens and consolidations on TUS in feedlot cattle, at both individual and group levels. Animals: A total of 221 bulls, aged 8.8 months and weighing 322.5 ± 160 kg, from nine farms. Methods: Cross-sectional study including all data from clinical examinations and TUS collected weekly during the first month on feed. Pathogens were assessed by seroconversion (all animals) and qPCR on nasal swabs (sick animals). At the individual level, the association between pathogen detection and TUS consolidation was investigated using univariate logistic regression, and the ability of consolidation size to differentiate bacterial from non-bacterial pneumonia was assessed using receiver operating characteristic curves. Principal component analysis identified clusters at the group level based on pathogen detection and TUS results. Results: At the individual level, bulls infected with multiple pathogens (odds ratio [OR], 8.1; 95% confidence interval [CI], 2.21–29.8) or a single virus (OR, 5.49; 95% CI, 1.42–21.3) were more likely to have consolidations than those not infected. A total consolidation size > 14 cm2 in the scanned thoracic region differentiated bacterial from non-bacterial pneumonia with a sensitivity of 47.8% (95% CI, 36.4–83.3) and specificity of 94.1% (95% CI, 60.0–100.0). These results were consistent at the group level; clustering based on bacterial versus non-bacterial etiology correlated with the number and size of consolidations. Conclusions and Clinical Importance: Consolidation size could help differentiate bacterial from non-bacterial pneumonia, guiding treatment at both individual and group levels.

Les bronchopneumonies infectieuses (BPI) représentent un enjeu sanitaire et économique majeur chez les jeunes bovins (JB) en début d’engraissement. Leur diagnostic repose encore largement sur l’observation de signes cliniques, avec une performance globalement faible. Cet article présente les avancées récentes concernant le diagnostic et le pronostic des BPI, en s’appuyant sur des études menées en conditions de terrain. L’échographie pulmonaire apparaît comme un examen complémentaire prometteur, permettant d’objectiver les lésions pulmonaires et d’orienter l’étiologie, malgré des limites spécifiques aux jeunes bovins. L’étude de la réponse immunitaire montre un intérêt pronostique potentiel de certains biomarqueurs. Enfin, les outils d’aide à la décision et les capteurs connectés offrent des perspectives intéressantes pour une détection plus précoce et une aide à la décision thérapeutique. L’absence de test diagnostique ou pronostique totalement satisfaisant souligne la nécessité d’approches intégrées combinant données cliniques, échographiques, biologiques et numériques, afin d’améliorer la prise en charge des BPI.

Les bronchopneumonies infectieuses (BPI) constituent une cause majeure de morbidité chez les jeunes bovins (JB) en engraissement, et entraînent des conséquences économiques et sanitaires importantes. Cette thèse émet l’hypothèse que la combinaison de plusieurs méthodes complémentaires permettrait d’améliorer les performances diagnostiques et pronostiques des examens actuellement disponibles ou encore à l’étude. L’échographie pulmonaire a été évaluée et validée chez les JB de race allaitante en tant qu’examen diagnostique pertinent, bien que probablement moins sensible que chez les veaux laitiers, avec un intérêt potentiel pour l’orientation étiologique. Parallèlement, l’analyse multiplex de quinze cytokines et chimiokines a permis de mieux caractériser la réponse immunitaire associée aux BPI, en lien avec les antécédents médicaux des animaux, et d’identifier plusieurs biomarqueurs prometteurs à visée pronostique. Enfin, une revue de la littérature des règles de prédiction clinique issues de la médecine humaine, utilisées dans le cadre de la pneumonie acquise en communauté (PAC) a été conduite pour proposer une transposition adaptée à la médecine bovine. Ce travail souligne l’intérêt d’une approche intégrée pour une gestion raisonnée et plus précise des BPI en élevage.