Determining Frequency of Common Pulmonary Gross and Histopathological Findings in Feedyard Fatalities

SIMPLE SUMMARY: Respiratory disease continues to play a major role in deaths seen in feedlot cattle. The most common respiratory diseases include bronchopneumonia, acute interstitial pneumonia, and bronchopneumonia with an interstitial pneumonia. Necropsy is a useful tool to collect information and enhance decision making about the health and management of a pen or lot. A more refined diagnosis and estimation of pulmonary lesions in all cattle, regardless of clinical signs, can provide a more accurate estimate of respiratory disease frequency. A diagnosis was determined during necropsy and further diagnostics were submitted for histopathologic evaluation to determine the agreement between the two diagnostics modalities. Both methods reported similar frequencies between the three most common respiratory diseases. The most frequent respiratory diseases recognized were bronchopneumonia and bronchopneumonia with an interstitial pneumonia. Recognizing bronchopneumonia with an interstitial pneumonia from bronchopneumonia and acute interstitial pneumonia can be an important component to understanding these disease processes and the cattle affected. ABSTRACT: Pulmonary disease is often associated with feedlot cattle mortality, and the most common syndromes include bronchopneumonia, acute interstitial pneumonia, and bronchopneumonia with an interstitial pneumonia. The study objective was to utilize gross necropsy and histopathology to determine the frequency of pulmonary lesions from three major syndromes and agreement between gross and histopathological diagnosis. A cross sectional, observational study was performed at six U.S. feedyards using a full systematic necropsy to assess mortalities during summer 2022. A subset of mortalities had four lung samples submitted for histopathological diagnosis. Gross necropsy was performed on 417 mortalities, 402 received a gross diagnosis and 189 had a histopathological diagnosis. Descriptive statistics were used to evaluate pulmonary diagnosis frequency based on method (gross/histopathology), and generalized linear mixed models were used to evaluate agreement between histopathological and gross diagnoses. Using gross diagnosis, bronchopneumonia represented 36.6% of cases with acute interstitial pneumonia and bronchopneumonia with an interstitial pneumonia representing 10.0% and 35.8%, respectively. Results identified bronchopneumonia with an interstitial pneumonia as a frequent syndrome which has only been recently reported. Histopathological diagnosis had similar findings; bronchopneumonia represented 32.3% of cases, with acute interstitial pneumonia and bronchopneumonia with an interstitial pneumonia representing 12.2% and 36.0%, respectively. Histopathological diagnosis tended (p-VALUE = 0.06) to be associated with gross diagnosis. Pulmonary disease was common and both diagnostic modalities illustrated three primary syndromes: bronchopneumonia, acute interstitial pneumonia, and bronchopneumonia with an interstitial pneumonia with similar frequencies. Improved understanding of pulmonary pathology can be valuable for evaluating and adjusting therapeutic interventions.