Evaluation of endocrine and immune responses of steers challenged with infectious bovine rhinotracheitis virus

The objective of this study was to evaluate the endocrine and immune responses of steers challenged with infectious bovine rhinotracheitis virus (IBRV). For the study, twelve crossbred beef steers weighing approximately 228.82 kg were fitted with indwelling rectal temperature monitoring devices and randomly assigned to a Control (CON) or IBRV treatments. Immune challenged steers received an intra-nasal dose of IBRV (4 ml total volume; 2ml/nostril) and CON steers received an intra-nasal dose of saline (2 ml/nostril). On day 0, steers were challenged and placed into isolated paddocks. At 72 hours post-inoculation, steers were fitted with indwelling jugular catheters and placed into individual stanchions. Blood samples were intensively collected on days 4 through 8 post-inoculation. Serum was analyzed for cortisol, interleukin-6, interferon-gamma, tumor necrosis factor-alpha, growth hormone, and insulin-like growth factor-1. On day 2, IBRV challenged steers had increased rectal temperature compared to CON steers (P < 0.05); the greatest rectal temperatures were observed on day 4, after which rectal temperatures returned to baseline by day 6. Serum concentrations of cortisol, interferon-gamma, and growth hormone exhibited a similar response pattern increasing by day 2 for the IBRV challenged steers, with the greatest increases observed on day 4, and subsiding on day 6. There was a decrease (P = 0.04) in growth hormone production in IBRV challenged steers, but no difference in insulin-like growth factor-1. Collectively, the data revealed that alterations in the somatotrophic axis were not associated with large increases in circulating pro-inflammatory cytokines. Results suggest that the dose of the virus used in the present study, while sufficient to elicit a febrile response, was not enough to elicit a robust pro-inflammatory immune response.