| Abstrakt: |
Bovine respiratory disease (BRD) contributes to high rates of mortality and morbidity among feedlot animals. Thus, there is a need to discover robust predictive biological indicators of infection status and disease severity in feedlot cattle. This study aimed to explore the use of 1 H nuclear magnetic resonance (NMR) based metabolite profiling to characterize serum molecular markers associated with a viralbacterial respiratory disease challenge in beef cattle. Crossbred beef steers [n = 24; initial body weight (BW) = 293 kg) were inoculated intranasally with bovine herpes virus-1 (2×108 PFU) and intratracheally with Mannheimia haemolytica (MH, 2.15×1010 CFU) on d -3 and 0, respectively (n = 16; MH-challenge), or similarly inoculated with phosphate-buffered saline (n = 8; Control-challenge). Blood was collected via jugular venipuncture on d -3, -1, 0, 2, 3, 5, 7, 10, and 14 relative to MH challenge for complete blood count and haptoglobin analysis, with additional serum samples stored at -80°C for subsequent metabolomic analysis. Continuously recorded variables included rumen temperature, activity, rumination, dry matter intake, and feeding behavior. Wottlin et al. (2020) reported that rumen temperature was increased (P < 0.04) in MH-challenged steers until d 6 post-MH inoculation (40.8 vs 39.3°C in MH-challenged and Controlchallenged steers several hours post-MH inoculation). Dry matter intake was reduced (P < 0.01) by 42% in MH-challenged compared with Control-challenged steers during the 14-d post-MH inoculation period. Further, haptoglobin concentrations were increased (P < 0.05) in MH-challenged steers from d 2 to 7 of the post-MH inoculation period. Serum samples underwent small molecule metabolite extraction and untargeted ¹ H NMR metabolomics. The ¹ H NMR spectra of serum metabolites were evaluated for this study, resulting in the unambiguous identification and quantification of 64 polar metabolites. Univariate analysis was conducted to examine the effect of the MH challenge on relative metabolite concentrations between d 2 and 5 relative to MH challenge, indicating differences between metabolites of MH-challenge and Control-challenged steers. However, multivariate analysis using unsupervised 2-dimensional principal component analysis (2D-PCA) could not differentiate MH-challenged from Control-challenged steers based on distinct serum metabolite profiles. Results indicate the potential of specific metabolites to indicate BRD infected cattle; however, a larger cohort of cattle and expanded metabolite profile coverage may be required to more fully differentiate between BRD vs healthy cohorts. Opportunities exist to further investigate the role of metabolomics to discover robust early biological indicators that are predictive of the onset of BRD in feedlot cattle. [ABSTRACT FROM AUTHOR] |
