Bronchopneumonia with interstitial pneumonia in feedlot cattle: Epidemiologic characteristics of affected animals

Abstract

Bronchopneumonia with interstitial pneumonia (BIP) of feedlot cattle is characterized by gross and histologic lesions of cranioventral bronchopneumonia (BP) and caudodorsal interstitial pneumonia. This study described the characteristics and frequency of BIP in western Canadian feedlot cattle and identified epidemiologic differences between BIP and either BP or acute interstitial pneumonia (AIP). The study of 9909 deaths on 4 western Canadian feedlots included 1105 BIP, 1729 BP, and 878 AIP cases. A population of 55 cases with gross, histopathology, and microbiology data was used to validate the primary data set. BIP was the second most common reason for death (or euthanasia) from respiratory disease (1105/9909 cases), and the observed frequency was twice what was expected from random concurrence of BP and AIP. Based on logistic regression models, epidemiologic characteristics of BIP were comparable to those of BP, although BIP cases were more chronic with more instances of clinical illness prior to death. BIP was epidemiologically distinct from AIP. Specifically, BIP more frequently affected steers than heifers, deaths occurred earlier in the feeding period at lower body weights and lower daily weight gains, and BIP cases had longer durations from the first clinical illness to death and more separate instances of clinical illness prior to death. Furthermore, death from BIP mainly occurred in winter and fall, while death from AIP was most frequent in summer. These findings define BIP as a unique condition of feedlot cattle and suggest that chronic BP may promote the development of fatal interstitial lung disease in at-risk cattle.

Keywords: atypical interstitial pneumonia; beef; bovine respiratory disease; calves; epidemiology; lung; pathogenesis; pathology.

Figure 1.

Gross lung lesions in cases of bronchopneumonia (BP), acute interstitial pneumonia (AIP), and bronchopneumonia with interstitial pneumonia (BIP) in feedlot cattle. (a) Normal lung. (b) BP. The cranioventral lung (BP) is red-purple and sharply demarcated from the normal caudodorsal lung (N). (c) AIP. Throughout the lung, most tissue is purple, whereas some lobules have a normal pink color. The lung fails to collapse and appears overinflated, with slight bulging from the cut surface, and subpleural and interlobular emphysema is present (*, and cut surface). (d) BIP. The caudodorsal area (IP) has lesions similar to AIP described above. The cranioventral area (BP) is red-purple as described above for BP.

Figure 2.

Histologic lung lesions in feedlot cattle. (a) Normal lung including alveoli (A) and bronchiole (B). (b) The alveoli (A) and bronchiole (B) are filled with neutrophils and macrophages, as would be present in cases of either bronchopneumonia (BP) or bronchopneumonia with interstitial pneumonia (BIP). Attenuation of bronchiolar epithelium is present but is not required for the diagnosis of BP. (c) Alveoli are lined by eosinophilic hyaline membranes (arrows). (d) The bronchiolar epithelium is attenuated (arrows). Neutrophils and macrophages are present in the lumen but are not required for the diagnosis of acute interstitial pneumonia (AIP) or BIP. Alveolar hyaline membranes (c) or type II pneumocyte proliferation are required for the diagnosis of AIP or BIP and bronchiolar necrosis (d) is typically present in these cases.

Figure 3.

Comparison of cattle with postmortem diagnoses of bronchopneumonia (BP, n = 1729), bronchopneumonia with interstitial pneumonia (BIP, n = 1105), and acute interstitial pneumonia (AIP, n = 878), with respect to the distribution of (a) sex, (b) postmortem weights, (c) time between arrival to the feedlot and death, (d) time from the first clinical illness to death (note the y-axis log₂ scale to show differences among groups), (e) number of separate instances of clinical illness, and (f) season in which the death occurred. The data show the percentage of cases for each diagnosis.

Figure 4.

Frequency of mortalities by month in cattle with postmortem diagnoses of bronchopneumonia (BP, n = 1729), bronchopneumonia with interstitial pneumonia (BIP, n = 1105), and acute interstitial pneumonia (AIP, n = 878). BP deaths were most frequent in December. BIP was most frequent in February (or December, in 2017). AIP frequency showed 2 peaks: the first in February to March usually corresponding to the peak of BIP frequency, and a second peak in July to August (or May, in 2019).