Transportation stress alters the circulating steroid environment and neutrophil gene expression in beef bulls

Stress and its association with altered immune function and incidence of respiratory diseases in cattle have lead to concerns over animal health and welfare during truck transportation. Previously, bulls subjected to transportation stress displayed altered expression of candidate neutrophil genes, warranting a broader investigation of the neutrophil transcriptome and possible associations with fluctuations in circulating steroid hormones. In the current study, blood was collected from six Belgian BluexFriesian bulls at -24, 0, 4.5, 9.75, 14.25, 24, and 48h relative to initiation of 9h of truck transportation. Plasma concentrations of cortisol, dehydroepiandrosterone (DHEA), progesterone, and testosterone were measured; cortisol:DHEA ratios were computed. Neutrophil gene expression was monitored by microarray analysis using bovine immunobiology (BOTL-5) microarrays. Eighty-eight genes were identified as being differentially expressed at P<0.05. Putatively affected genes were grouped into ontological clusters; those of greatest interest for qRT-PCR validation were involved in immune response, apoptosis, wound healing, and several of currently unknown function. Confirmed gene expression changes supported the dramatic effects of transportation stress on the bovine neutrophil transcriptome. Temporal correlations between gene expression profiles and circulating total leukocyte and neutrophil counts were apparent. However, few relationships between gene expression and plasma steroid profiles were detected, possibly due to the biological time-lag between these variables not captured by the blood collection schedule. Further investigation into the factors underlying neutrophil gene expression changes and validations at the protein and cell behavior levels will lead to a better understanding of altered innate immunity in cattle during transportation stress.