Respiratory tract infections are the leading cause of antimicrobial use in calves. Combining clinical examination and lung ultrasonography allows on-farm classification of calves as healthy or suffering from an upper respiratory tract infection (URTI), subclinical or clinical pneumonia. This might help to improve targeted antimicrobial therapy, restricting treatment to pneumonic cases. However, to what extent these diagnostic categories coincide with expected bacteriological and cytological bronchoalveolar lavage fluid (BALf) characteristics is currently unknown. The objective of this study was therefore to compare BALf bacteriology and cytology between healthy calves and calves with URTI, subclinical and clinical pneumonia. The hypothesis was that calves with subclinical and clinical pneumonia would have higher quantitative bacterial counts, bacterial isolation rates and neutrophil counts than URTIs or healthy animals. A cross-sectional study was performed on 305 indoor group-housed dairy and beef calves, from 62 farms. Calves were classified by combining clinical examination and lung ultrasonography. Clinical respiratory disease was defined using the Wisconsin score card and the Healthy Criterion (HC). The HC classified calves as clinically ill if at least one clinical sign was present. Ultrasonographic lung consolidation with a depth of ≥1 cm was considered indicative for pneumonia. Cytology and bacteriology were performed on BALf sampled by non-endoscopic bronchoalveolar lavage. Calves with clinical pneumonia were further subdivided based on culture result and presence of neutrophils phagocytosing bacteria. Combined lung ultrasonography and clinical examination (HC) classified 25.9 % (79/305) of the calves as healthy, 33.1 % (101/305) as URTI, 10.2 % (31/305) as subclinical and 30.8 % (94/305) as clinical pneumonia. Bacterial isolation rates and quantitative BALf culture results did not differ between groups. Calves with clinical pneumonia and neutrophil phagocytosis showed a significantly higher BALf neutrophil percentage compared to healthy calves (59.0 % vs. 37.7 % in healthy calves, P =.03). Inversely, lymphocyte percentage was lower in these calves (1.8 % vs. 5.3 % in healthy calves, P = .003). Classification of calves using lung ultrasonography and clinical scoring did not correspond with BALf bacteriology and cytology findings, as extrapolated from human and companion animal medicine. Under the current housing conditions of this study high rates of non-infectious airway inflammation or airway colonization by opportunistic pathogens, rather than infection might explain this. Isolation of respiratory pathogens from calves with various signs of respiratory disease or ultrasonographic lesions should be interpreted carefully. Of all cytological features, phagocytosis by neutrophils in BALf might be a useful criterion supporting the diagnosis of bacterial respiratory tract infection.

中文翻译：

---

基于联合临床评分和肺部超声检查对小腿细支气管肺泡灌洗液细菌学和​​细胞学的比较。

呼吸道感染是犊牛使用抗菌药物的主要原因。将临床检查和肺部超声检查相结合，可将小牛在农场上分类为健康或患有上呼吸道感染（URTI），亚临床或临床肺炎。这可能有助于改善靶向抗微生物治疗，将治疗仅限于肺炎病例。但是，目前尚不清楚这些诊断类别在多大程度上与预期的细菌学和细胞学支气管肺泡灌洗液（BALf）特征相吻合。因此，本研究的目的是比较健康小牛和患有URTI，亚临床和临床肺炎的小牛之间的BALf细菌学和细胞学。假设是，患有亚临床和临床肺炎的小牛的细菌数量会更高，细菌分离率和中性粒细胞计数要比URTIs或健康动物高。对来自62个农场的305个室内群养奶牛和小牛犊进行了横断面研究。通过临床检查和肺部超声检查对小牛进行分类。使用威斯康星州记分卡和健康标准（HC）定义临床呼吸系统疾病。如果存在至少一种临床体征，HC将小牛分类为临床病。深度≥1cm的超声肺巩固被认为是肺炎的征兆。细胞学和细菌学是通过非内镜支气管肺泡灌洗对BALf进行的。根据培养结果和嗜中性粒细胞吞噬细菌的存在，进一步细分具有临床肺炎的小牛。合并肺部超声检查和临床检查（HC）的类别为25。健康的小牛为9％（79/305），URTI为33.1％（101/305），亚临床为10.2％（31/305），临床肺炎为30.8％（94/305）。两组之间的细菌分离率和定量BALf培养结果无差异。与健康犊牛相比，患有临床性肺炎和嗜中性粒细胞吞噬作用的犊牛表现出更高的BALf嗜中性粒细胞百分比（健康犊牛为59.0％，而健康犊牛为37.7％，P = .03）。相反，这些小牛的淋巴细胞百分比较低（健康小牛为1.8％，而小牛为5.3％，P = 0.003）。从人类和伴侣动物医学推断出，使用肺部超声检查和临床评分对小牛进行分类与BALf细菌学和细胞学发现不符。在本研究的当前居住条件下，机会性病原体而非感染的非传染性气道炎症或气道定植率很高，这可能解释了这一点。应仔细解释从犊牛身上分离出呼吸道病原体的迹象，这些犊牛具有各种呼吸道疾病或超声检查病灶。在所有细胞学特征中，BALf中嗜中性粒细胞的吞噬作用可能是支持细菌性呼吸道感染诊断的有用标准。