Application of thoracic ultrasonography for the diagnosis of Bovine Respiratory Disease in Piedmontese calves

Bovine respiratory disease (BRD) is one of the main health issues in calves. Thoracic ultrasonography (TUS) was found to be a promising tool in detecting BRD¹. The aim of this prospective study was to describe findings of TUS, clinical examination and bacteriology in post-weaned Piedmontese calves. Animals were examined at 3 experimental times: T0 (day of inclusion), T1 (7 days), T2 (21 days). Data about clinical examination and TUS findings (2-5 MHz convex probe) were recorded for each calf at T0, T1 and T2. TUS was performed on 4 standardized areas of both hemithoraxes: cranio-dorsal (CrD), cranio-ventral (CrV), caudo-dorsal (CaD), caudo-ventral (CaV). TUS findings were classified by mean of a scoring system (USc- 0: no lesions; 1: comet-tail artifacts; 2: lobular consolidation; 3: lobar consolidation)¹. At T0 nasal swabs (NS) and trans-tracheal aspiration (TTA) samples were collected for bacterial culture. Data analysis [Wilcoxon signed rank test, Sensitivity (Se), Specificity (Sp)] was performed with statistical software R, v. 3.2.3. Data were reported as median (min-max), statistical significance was set at P < 0.05. Twenty calves, aged between 5 and 14 months, from 5 herds, were included. At T0, 14/20 (70%) animals were classified as BRD affected according to TUS findings. Only 9/20 (45%) had concomitant clinical signs. Lesions were found on both hemithoraxes in 8/14 (57%) calves and involved the CrV area in the 78% of cases. Four calves without abnormal TUS findings at T0 have developed lesions at T1 (n=3) and T2 (n=1). Median USc was 3 (0-12) at T0, 4 (0-10) at T1 and 4.5 (0-11) at T2. Statistical difference in USc was found between T0 and T2 (p=0.03). Overall, pathogenic bacteria of BRD [Mycoplasma spp. (56%), P. multocida (28%), M. haemolytica (11%) and T. pyogenes (5%)] were found in 14 TTA samples. Of these, 11 came from calves with TUS lesions at T0, while 3 were from calves that developed TUS lesions at T1 and T2. Bacterial culture of NS led to the identification of BRD pathogens in 57% (8/14) of positive TTA samples. Clinical examination showed low sensitivity compared to both TUS (Se: 64%, Sp: 100%) and bacterial culture of TTA samples (Se: 50%, Sp: 67%). TUS had 79% of Se and 50% of Sp compared to TTA culture. Results of the present study suggest TUS as a promising tool for the diagnosis of BRD in post-weaned Piedmontese calves. This technique can be a practical screening method in field condition, allowing the characterization of lung lesions. According to studies in dairy calves¹’², TUS had a higher sensitivity for BRD diagnosis when compared to clinical examination. Moreover, TTA samples seems to be more appropriate than NS for bacteria detection. Our investigation led to a higher Mycoplasma spp. detection compared to other pathogens, showing its important role in the pathogenesis of BRD. ¹Ollivett T.L. et al - 2016. On-Farm Use of Ultrasonography for BRD. Vet. Clin. North Am. Food Anim. Pract. 32, 19–35. ²Buczinski S. et al - 2014. Comparison of thoracic auscultation, clinical score, and ultrasonography as indicators of BRD in preweaned dairy calves. J. Vet. Intern. Med. 28, 234–42.