Bronchopneumonia with interstitial pneumonia in beef feedlot cattle: Characterization and laboratory investigation

Abstract

Bronchopneumonia with interstitial pneumonia (BIP) has been considered a variant of acute interstitial pneumonia (AIP) rather than a distinct disease. This study compared 18 BIP, 24 bronchopneumonia (BP), and 13 AIP cases in feedlot beef cattle. Grossly, BIP cases typically had cranioventral lung lesions of similar morphology and extent as BP cases, but the caudodorsal lung appeared overinflated, bulged on section, and had interlobular edema and emphysema. Gross diagnosis of BIP had 83% sensitivity and 73% specificity relative to histopathology. Histologic lesions of BIP in cranioventral areas were of chronic BP, while caudodorsal lesions included alveolar and bronchiolar damage and inflammation, interstitial hypercellularity, and multifocal hemorrhages. In BIP cases, cranioventral lung lesions were more chronic than caudodorsal lesions. Histologic scores and microbiology data were comparable in cranioventral lung of BIP versus BP cases and caudodorsal lung of BIP versus AIP cases, with differences reflecting a more chronic disease involving less virulent bacteria in BIP versus BP. Mycoplasma bovis infection was similarly frequent among groups, and a viral cause of BIP was not identified. Lesion morphology and similar blood cytokine concentrations among groups argued against sepsis as a cause of lung injury. Surfactant dysfunction was identified in BIP and BP, and was only partially the result of protein exudation. These and other findings establish BIP as a distinct condition in which chronic cranioventral BP precedes acute caudodorsal interstitial lung disease, supporting a role of chronic inflammation in heightened sensitivity to 3-methylindole or another lung toxicant.

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

“…Overall, the study results suggest that BIP is a distinct condition of feedlot cattle with differences from AIP, even though cranioventral and caudodorsal lung lesions of BIP are pathologically and microbiologically similar to those of BP and AIP, respectively. 4 …”

“…Descriptive statistics were compared among postmortem diagnosis groups, including the proportion of deaths attributed to BIP, sex distribution (steers, heifers, or bulls), postmortem weight, days on feed, average daily weight gain, days from the first signs of clinical illness until death, number of separate instances of clinical illness prior to death, season of death, and presence of fever upon arrival to the feedlot. 4 For this study, clinical illness was restricted to temporally separated incidents diagnosed as “arrival fever,” “undifferentiated fever,” “no fever,” or “AIP.”…”

“…The gross and histopathology, microbiology, and other findings are reported elsewhere. 4 Of these 55 cases, 25 were included in the primary data set of 9909 cases. In contrast to the primary data set, in which assignment of cases to study groups was based on gross diagnoses made by multiple feedlot veterinarians, diagnoses in these 55 cases were based on histological diagnosis ( Fig.…”

“…This has been termed feedlot IP (ie, a “variant” of feedlot AIP) or secondary IP, 2 , 9 but BIP is the favored term based on the morphologic features used for diagnosis. 4 …”

“…The results suggested that in BIP cases, chronic inflammation resulting from bacterial infection of cranioventral lung might increase the sensitivity to a lung toxicant (eg, 3-methylindole), with subsequent damage to alveoli and bronchioles. 4 …”