Bovine respiratory disease (BRD) is one of the most important diseases in feedlot calves especially in intensely raised and newly transported calves. In view of the importance of BRD and the need to reduce antimicrobial use in food producing animals, there is growing interest in developing novel strategies to enhance host immune defenses against respiratory pathogens.
Therefore, this study was planned to throw more light on the following points: investigate the diagnostic utility of computer-aided lung scoring system and lung ultrasonography at initial diagnosis of naturally occurring BRD in feedlot cattle, figure out whether blood LAC and serum biochemical markers (acute phase protein and pro-inflammatory cytokines) can be utilized to anticipate the event of BRD in feedlot cattle, characterize the composition, structure and relationship of the lower and upper respiratory microbial communities in clinically healthy feedlot cattle. Finally, characterize the nasopharyngeal microbiota of feedlot cattle at entry into a commercial feedlot, during initial management processing, and to compare the dynamics of change in these microbial communities between clinically healthy calves and those that develop BRD within the first month after entry.
A total of one hundred thirty-five feedlot calves at high risk of developing BRD were monitored daily during the first month after entry at the feedlot for clinical signs of BRD. Of the 135 steers, 22 BRD cases with 22 pen matched healthy controls calves were enrolled in our study. Blood sample, nasopharyngeal swabs (NPS) and bronchoalveolar lavage (BAL) fluid were collected at entry during processing, at initial diagnosis of BRD. For each calf examined for BRD, one pen matched apparently healthy calf was selected as control and sampled in the same manner.
All feedlot calves with visual signs of BRD had abnormal lung sounds with lung scores ranging from 2 to 5. Moreover, lung ultrasonography identified lung lesions in 70.83% from BRD affected calves and 12.5% from pen matched controls. Logistic regression model revealed blood LAC during initial processing was significantly associated with odds of becoming a BRD case in calves revealing lung score 2.
The nasopharyngeal microbiota of healthy and BRD affected calves were distinct from each other with the diseased calves exhibiting less diversity and fewer observed species compared to healthy controls. Discriminant analysis revealed that the nasopharyngeal microbiota in feedlot calves at entry resembles that of BRD affected calves, but differs from pen matched healthy calves and this similarity between processing and BRD groups might explain why cattle are most likely to be affected with BRD during the first month after entry.
Most of the bacterial genera identified in the BAL samples were also present in the NPS, but biogeographical-specific genera were enriched in both the NPS (Rathayibacter) and BAL (Bibersteinia) samples. There were strong associations between the presence of certain taxa at each specific location, and strong correlations between the presence of specific taxa in both the NPS and BAL samples, supporting the notion of a mutualistic interrelationship between these microbial communities. Further studies in large cohorts of animals are needed to determine the role and clinical importance of the relationships of respiratory tract microbial communities with health, productivity, and susceptibility to the development of respiratory disease, in growing cattle.
|
