Abstract
Bovine respiratory disease (BRD) is caused by complex interactions between viral and bacterial pathogens, host immune status, and environmental stressors. In both clinical and research settings, current methods for detecting BRD in calves commonly focus on visual indicators such as attitude, nasal discharge, and cough, in addition to vital signs such as rectal temperature and respiration rate. Recently, thoracic ultrasonography (TUS) has become more commonly used in clinical settings, in addition to physical examination to diagnose BRD. To assess the value of performing TUS during experimental BRD infection, 32 calves were challenged with bovine respiratory syncytial virus, to mimic a viral infection, and 30 calves were infected with Mannheimia haemolytica, to mimic a bacterial infection. TUS was performed at regular intervals using a standardized method and scoring system in addition to daily clinical scoring. Although overall correlations between clinical scores and TUS scores were generally weak (maximum R2 = 0.3212), TUS identified calves with abnormal lung pathology that would have otherwise been misclassified on the basis of clinical scoring alone, both on arrival and throughout the studies. In addition, TUS had an increased correlation with gross lung pathology on necropsy (maximum R2 = 0.5903), as compared to clinical scoring (maximum R2 = 0.3352). Our results suggest that TUS can provide additional information on calf health at enrollment and throughout a study and may provide an alternative to terminal studies, due to the high correlation with lung pathology at necropsy.
Highlights
Bovine respiratory disease (BRD) is a leading cause of morbidity and mortality among preweaned dairy calves and is a major health concern among feedlot cattle [1, 2]
Lung auscultation performed by an experienced veterinarian can improve the accuracy of clinical scoring models; studies have suggested that this method may lack sensitivity for diagnosing BRD [6], and it is difficult to assign a quantitative score
Because of elevated clinical disease scores, two calves were euthanized on day 6, and four calves were euthanized on day 7
Summary
Bovine respiratory disease (BRD) is a leading cause of morbidity and mortality among preweaned dairy calves and is a major health concern among feedlot cattle [1, 2]. Current detection methods primarily focus on clinical scoring, which relies on indicators such as rectal temperature, difficulty breathing, increased respiration, ear position, and nasal discharge [5]. These indicators have a low sensitivity and specificity for lesions within the lung [6]. Many of TUS Use in Experimental BRD these clinical signs such as temperature and depression can be caused by environmental conditions and are nonspecific disease indicators [7]. Research of potential BRD interventions is often performed with controlled infections using clinical scoring as the main method of determining the severity of disease progression. With the current detection methods, many markers of disease severity in these intervention studies can only be observed post-mortem, limiting the ability to analyze disease progression longitudinally
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