Bovine respiratory disease: healing process of lung lesions after florfenicol and meloxicam treatment in veal calves

Clinical examination (CE) of respiratory signs during bovine respiratory disease (BRD) is not indicative of the healing process in consolidated lungs following treatment. In contrast, lung ultrasonography (LUS) has gained recognition as performant tool to detect BRD that can be used to document the healing process. The aim of this study was to use the LUS as investigation tool to evaluate the lung healing process following florfenicol and meloxicam treatment. Animal care and procedures were in accordance with the European Directive 2010/63/EU and the national law D.L. 2014/26. A single stock of 84 veal calves were enrolled with an average age of 30.6±9.6d at arrival. CE and LUS examinations were performed on each animal. Nasal and ocular discharges, rectal temperature, cough, ear position, and abnormal breathing were assessed to calculated two clinical scores: Wisconsin (BRD≥4) and California (BRD≥5) Scores. The LUSs were used to establish ultrasonography score (US; 0-5 points score) and modified lung lesion score (LLS; BRD≥10.5). Lung consolidations were measured to provide thickness (cm) and area (cm2) of each lesion. The sum of all consolidated areas provided the total lung consolidation area (TLC; cm2). Animals with the US≥3 or consolidation thickness ≥3cm on cranial region were treated with one-shot of florfenicol and meloxicam (40mg/Kg+0.5mg/Kg; Zeleris®, Ceva Santé Animale). Treated group (TRT; n=36) was monitored at +1, +3, +5, +7, +9, +11, and +14d post-treatment. The non-treated animals during the production cycle were classified as control group (CTR; n=48). Differences over production cycle, CE and LUS follow-ups were assessed by PROC GLIMMIX procedure of S.A.S.-software. Groups comparisons were performed at arrival, treatment days, and at the day before slaughter of each animal. A post-hoc pairwise comparison was performed using Bonferroni correction. A p-value<0.05 was accepted. At their arrival, no differences were found between groups. Clinical scores, US, LLS, and TLC were significantly higher in TRT vs. CTR at the treatment day. At the end of the study, clinical scores and LUS examinations were similar or marginally different between groups. In addition, growth performances and beef quality were similar in both groups. A vast majority of BRD cases (88.9%) occurred within first 30d after arrival with another 11.1% occurring until 60d. Overall BRD treatment success rate was 94.3%. BRD chronicity rate was 2.9%; and fatality rate was 2.9%. Interestingly in TRT calves, overall clinical scores were indicative of disease at +5d after treatment (Wisconsin 4.5±0.6; California 5.7±0.8) but not at treatment day. US, LLS and TLC were high at the day of BRD diagnosis (US=4.7±0.3; LLS=15.6±1.9; TLC=30.06±1.98cm2) with cranial regions showing the largest lesions as determined by consolidation thicknesses and areas. Following treatment, a swift lung healing process was observed with significative decrease in US at +3d, +5d, +11d; in LLS at +1d, +5d, +7d; and in TLC at +1d, at +5d, and at+9d. In this field study in veal calves, BRD mainly occurred within the first month after arrival. Systematic LUS examinations, both US and LLS, allowed to detect BRD five days before clinical scores which ensured prompt treatment. The evaluation of the lung healing process also revealed the fast and beneficial effects of florfenicol and meloxicam in affected calves.