Multi-omics investigation into long-distance road transportation effects on respiratory health and immunometabolic responses in calves.

Background: Long-distance road transportation is a common practice in the beef industry, frequently resulting in bovine respiratory disease (BRD) and compromised growth performance. However, a comprehensive investigation integrating clinical performance, physiological conditions, and nasopharyngeal microflora remains lacking.

Methods: This study aimed to evaluate the respiratory health and immunometabolic status of 54 beef calves subjected to a 3000-km journey. The respiratory health of calves was monitored over 60 days post-arrival using a modified clinical scoring system. Nasopharyngeal microflora and venous blood samples were collected at 3 time points: before transportation (A), 30 days post-arrival (B), and 60 days post-arrival (C), for 16S rRNA microbiomics, whole-blood transcriptomics, serum metabolomics, and laboratory assays.

Result: Within the first week post-arrival, the appetite and mental scores of calves dropped to zero, while other respiratory-related scores progressively declined over the 60 days. The α-diversity of nasopharyngeal microflora in calves was similar at time points A and B, both significantly higher than at time point C. The structure of these microbial communities varied significantly across different time points, with a notably higher relative abundance of BRD-related genera, such as Pasteurella and Mannheimia, detected at time point A compared to B and C. The composition and gene expression profiles of circulating blood cells at time point A were significantly different from those at B and C. Specifically, higher expression levels of oxidative- and inflammatory-related genes, cytokines, and enzymes were observed at time point A compared to B and C. Higher levels of catabolism-related metabolites and enzymes were detected at time point A, while higher levels of anabolism-related metabolites and enzymes were observed at time points B and C. Additionally, significant correlations were found among microorganisms, genes, and metabolites with differing abundances, expression levels, and concentrations across time points. Stronger correlations were observed between calves' performance and nasopharyngeal microflora and immunometabolic status at time point A compared to B or C.

Conclusions: Collectively, these results confirm that 3000 km of road transportation significantly alters the composition and gene expression profiles of circulating white blood cells in calves, affects their metabolic processes, disrupts the balance of the respiratory microbial community, and leads to pronounced respiratory symptoms that persist for at least 60 days. During this period, the influenced composition and gene expression of circulating blood cells, metabolic processes, and nasopharyngeal microbial community gradually return to equilibrium, and the respiratory symptoms gradually diminish. This observational research indicates that transportation induces BRD in calves by disrupting the homeostasis of their immune function, metabolic processes, and nasopharyngeal microbial community. However, these results and their underlying molecular mechanisms warrant further validation through well-designed in vivo and in vitro confirmatory experiments with larger sample size. Video Abstract.