Graduate Student Colorado State University Fort Collins, CO, United States
Abstract: Background Bovine respiratory disease (BRD) is a leading cause of morbidity and mortality in cattle. Stress due to transport and weaning increases BRD risk, yet mechanisms of immune susceptibility following stress are less clear. Here we evaluated host-microbe interactions from bronchoalveolar lavage fluid (BALF) to understand immune responses to stress. Hypothesis/Objectives We hypothesized that stress would result in pulmonary immunomodulation, and that microbial populations would shift between stress and acclimation. Animals Stocker calves were purchased at auction and transported to a commercial backgrounder. A subset of healthy calves (rectal temperature < 103.5 ℉, no lung consolidation on lung ultrasound) were sampled for BALF within 24 hours (STRESSED; n=12) or acclimated to the backgrounding facility for 2-3 months before sampling (ACCLIMATED; n=7). Methods In this case-control study, BALF sampling was performed at the backgrounding facility, and BALF samples were processed for bulk transcriptomic (RNA-seq, STAR alignment pipeline) and 16S rRNA sequencing (Qiime2 analysis pipeline) separately. Gene expression data was analyzed in Cibersortx to predict abundance of major cell populations. Results RNA-seq profiles of stressed calves demonstrated over 350 differentially expressed genes. Key pathways upregulated included neutrophil migration, with an increase in neutrophil numbers predicted in STRESSED calves (2.5-fold increase, P < 0.01). Microbiome analysis demonstrated no difference in diversity metrics (P>0.05) despite the apparent immune activation. Conclusions and Clinical Importance In contrast to our hypothesis, these data demonstrate that healthy stocker calves at arrival have an increase in neutrophil-associated gene expression relative to acclimated calves, even as microbial diversity metrics demonstrate no differences.
