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The association of cough and other clinical signs with ultrasonographic lung consolidation: differences between dairy, veal and beef calves
Lowie, T., Van Leenen, K.,...
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Background
Bovine respiratory disease (BRD) remains a leading cause of economic losses, hampered animal welfare and intensive antimicrobial use in the cattle sector. The latter contributes to public concerns and awareness about the development of antimicrobial resistance. To reduce antimicrobial use without risking economic losses or compromising animal welfare, it appears rational to limit antimicrobial treatment to calves with pneumonia, while withholding this treatment for just an upper respiratory tract infection at first instance. A true gamechanger in recent years is the use of thoracic ultrasonography (TUS) on farm, which was evidenced to be the most accurate diagnostic test for pneumonia in calves. Despite that rapid ultrasound techniques have been developed to better meet practitioners demands, continuously scanning all animals is practically and economically impossible. Therefore, the need for the development of early warning systems based on clinical signs, to timely detect animals with pneumonia is ever growing. However, a wide variety of definitions, based on clinical signs, to identify cattle with respiratory disease requiring antimicrobial treatment have been used in science and practice. Also, current scoring systems can be quite time consuming, whereas it is not known whether it is necessary to score all signs. Available scoring systems were developed and tested almost exclusively in pre-weaned dairy calves. Therefore, the question arises which clinical signs are associated with ultrasound confirmed pneumonia and whether the same clinical signs can be used postweaning or in other breeds or different production systems.
Objectives
To identify which clinical signs are associated with ultrasonographic lung consolidation (≥1 cm) in different breeds, production types (dairy, beef and dairy-mixed), and pre- and post- weaning. To identify how well individual clinical signs performed in the detection of ultrasound confirmed pneumonia compared to BRD clinical scoring cards in a new dataset.
Material and Methods
A cross-sectional study was conducted in the northern part of Belgium (Flanders) between 2016-2019. 956 untreated calves (70% Holstein-Friesian dairy and 30% Belgian Blue) from 84 herds were conveniently selected. At enrollment, all calves were clinically examined using 24 parameters, scored using the Wisconsin and Davis BRD clinical scoring card and subjected to TUS. Associations between clinical signs and pneumonia were determined using a generalized linear mixed model. Herd was added as random factor to take clustering of calves within a herd into account.
Results
Cough, both spontaneous and/or induced cough, was the only and best performing clinical sign, significantly associated with lung consolidation in all production types. Fever (≥39.4°C) was the second most promising factor, being significant in beef and veal calves, but not in dairy calves. At last, respiratory rate (≥43 bpm), eye and nasal discharge were only of significance in veal calves. However, across the complete dataset spontaneous cough (Acc (Accuracy): 65.1%), induced cough (Tracheal reflex Acc: 61.1%, Larynx reflex Acc: 58.1%), rectal temperature (Acc: 61%), breathing rate (Acc: 61.3%) and eye discharge (Acc: 59.1%) were significantly associated. Postweaning, none of the clinical signs studied were associated with pneumonia, with the exception of cough in dairy calves. Further, cough as a single clinical sign outperformed any combination of clinical signs, including the Wisconsin (Acc: 62.8%) and Davis (Acc: 61.5%) respiratory disease scoring systems, but sensitivity remained low.
Conclusion
Cough outperformed existing scoring systems based on multiple parameters, but still had too low accuracy to be useful for decision making regarding antimicrobial treatment. Based on the present study, cough is best regarded as a group level warning that the respiratory tract reacts on pathogens, environmental factors or their combination. Rather than using clinical signs, TUS remains absolutely necessary to responsibly use antimicrobials, avoiding treatment of animals with only an upper respiratory tract infection. Next to cough, rectal temperature and breathing rate are the most promising clinical signs for further exploring in continuous monitoring systems for pneumonia detection in calves. Given that the association of clinical signs with ultrasonographic pneumonia differed between production systems, breeds, and weaning status, validation of a scoring system in each breed, age category and housing system is recommended.
Keywords: Bovine respiratory disease, pneumonia, scorecards, predictive monitoring, thoracic ultrasound.
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