Abstract
BACKGROUND: This study explored the combined use of fever detection and thoracic ultrasonography to identify calves with early onset bovine respiratory disease (BRD). Thoracic ultrasonography was then used to assess the efficacy of antimicrobial and non-steroidal anti-inflammatory drug (NSAID) treatment for early onset BRD through a randomised study design. METHODS: Calves were recruited from a single dairy farm in the UK, and fitted with a TempVerified FeverTag, which was activated when a calf developed fever (a temperature of 39.7°C for six hours). On identification of fever, a Wisconsin calf score was used to provide a diagnosis of BRD by exclusion of other causes. Calves were randomly assigned to experimental groups; group 1 (NSAID) received flunixin meglumine, group 2 (antimicrobial) received florfenicol, group 3 (both) received both drugs. A thoracic ultrasound was conducted within 48 hours of fever detection, and again 14 days later to assess lung pathology. RESULTS: A total of 152 calves were recruited, with a relative BRD prevalence of 49 per cent (74/152). Thirty-two calves required a secondary treatment (due to continued fever), causing exclusion from statistical analysis of the change in ultrasound score and resulting in the study being underpowered for detecting statistical significance. Initial thoracic ultrasound scores were very low, with 70/74 calves scoring either 0 or 1, indicating few comet tails and no lung consolidation was seen and potential overdiagnosis of BRD. For assessment of therapy efficacy, no effect of experimental group was detected on average daily growth rates (mean 0.85 kg/day, P=0.89). Calves also displayed very few clinical signs at the time of fever detection. These factors combined suggest a high rate of false positive identification (low specificity) for BRD through fever detection alone. Calves given the NSAID only were more likely to require repeat treatments due to fever recurrence (OR=3.10 (95 per cent CI 0.86 to 11.15), P=0.083). Also calves affected by their first case of fever at an older age (21 v 28 days old) were less likely to go on to have further fever episodes (OR=0.95 (95 per cent CI 0.90 to 0.99), P=0.026). CONCLUSION: This study demonstrated calves given only an NSAID at occurrence of fever due to BRD may be more likely to require repeat treatments throughout the preweaning period. The use of fever detection alone for BRD indicated a low specificity for definitive diagnosis as shown by the low thoracic ultrasound scores and lack of clinical signs. The study was underpowered to assess the ultrasonic effects of the different treatment protocols on lung pathology.