Impact of oral meloxicam and long-distance transport on cell-mediated and humoral immune responses in feedlot steers receiving modified live BVDV booster vaccination on arrival

The objective of this study was to investigate the impact of oral meloxicam (MEL) and long-distance transportation on cell-mediated immunity (CMI) in preconditioned steers receiving a booster vaccination on arrival. We hypothesized that steers treated with MEL at 1 mg/kg body weight, 6 h before night-time transport, would be less immunocompromised on arrival (day 0) and after 7 days, and that CMI following vaccination with a modified live bovine viral diarrhea virus (BVDV) recall antigen would be increased. Brahman crossbreed steers, 13–17 months of age (n = 87), were randomly assigned to one of four treatment groups: MEL, transported (MTR) (n = 22), MEL, non-transported (MNT) (n = 22), lactose placebo, transported (CTR) (n = 21), and lactose placebo, non-transported (CNT) (n = 22). MTR and CTR steers were transported for approximately 16 h non-stop on a truck from Mississippi to Iowa (approximately 1300 km), whereas steers in the MNT and CNT groups remained in Mississippi as non-transported controls. Body weight was measured and jugular blood was collected at −1, 0, and 7 days from all steers at the same time, regardless of location. Multi-parameter flow cytometry (MP-FCM) was used to identify T-cell subsets and detect the expression of three activation markers (CD25 [interleukin (IL)-2 receptor], intracellular interferon-gamma [IFNγ], and IL-4) after in vitro stimulation with BVDV recall antigen. Plasma cortisol concentration was measured on day −1, 0, and 7 as a marker of transport-associated stress. Serum antibody titer to BVDV was assessed on day −1 and day 7 post-booster vaccination. Whole-blood samples were analyzed using MP-FCM on days 0 and 7. Results were log transformed and analyzed using repeated measures of analysis of variance. Compared with non-transported controls, transport led to an increase in BVDV-induced expression of CD25, IFNγ, and IL-4 in CD4+, CD8+, and γδ+ T-cell subsets (P < 0.05). MEL treatment mitigated the transportation-associated increase in CD25 expression by peripheral blood mononuclear cells (PBMCs), CD4+, and γδ+ T cells. CMI outputs for the MTR group were less than those of the CTR group (P < 0.05); however, the MTR and NT groups did not differ (P > 0.10). A treatment*transport interaction was noted for the increase in IL-4 expression by CD8+ T cells after transport, with a significant difference between the CTR and MTR groups at day 7. In conclusion, the use of oral MEL prior to transport appears to have inhibitory or homeostatic effects, but further research is needed to validate the effect of MEL treatment on specific T-cell subsets in transported cattle.