Enhancement of the acute phase response to lipopolysaccharide in feedlot steers supplemented with OmniGen-AF
This study was designed to determine the effect of supplementing feedlot steers with OmniGen-AF on the acute phase response to a lipopolysaccharide (LPS) challenge. Steers (n=18; 270±5 kg BW) were separated into two treatment groups (n=9/treatment): one group was fed a standard receiving diet (Control, Cont) and the other group was fed the same receiving diet supplemented with OmniGen-AF at 4 g/45.4 kg BW for 29d (OmniGen-AF). On d27 steers were fitted with indwelling jugular cannulas and rectal temperature (RT) monitoring devices and placed in individual stalls. On d28, steers were challenged i.v. with LPS (0.5 µg/kg BW at 0 h). Sickness behavior scores (SBS) and two whole blood samples were collected at 30-min intervals from -2 to 8h relative to the challenge at 0h. One vacutainer containing EDTA was collected for complete blood cell count (CBC) analysis, and the second was collected in 9-mL monovette serum tube; after collection serum was isolated and stored at -80oC until analyzed for cortisol and cytokine concentrations. Rectal temperature, SBS, and cortisol were affected by time (P<0.001). Prior to the challenge, RT was greater (P<0.001) in Cont steers (39.31±0.03oC) than OmniGen-AF steers (39.14±0.03oC). Therefore, post-challenge RT was analyzed as the change in response from baseline values. The change in RT relative to baseline values increased (P<0.001) in both groups in response to LPS challenge, but was not affected by treatment (P=0.49). Sickness behavior scores increased (P<0.001) after LPS challenge and tended (P=0.09) to be greater in Control (1.57±0.02) than OmniGen-AF steers (1.51±0.02). Cortisol concentrations were affected by treatment (P=0.005) and time (P<0.001). For both groups, cortisol increased (P<0.001) in response to LPS challenge. Cortisol was greater in Cont (29.2±0.9 ng/mL) than OmniGen-AF steers (25.5±0.9 ng/mL). White blood cell and lymphocyte concentrations were greater (P≤0.004) in Cont than OmniGen-AF steers throughout the study. Neutrophils were decreased (P = 0.04) in Cont steers (0.7±0.2 K/uL) compared to OmniGen-AF steers (1.3±0.2 K/uL) prior to the LPS challenge. There was a treatment (P≤0.02) and time (P<0.001) effect for tumor necrosis factor-α (TNFα) and interferon-γ (IFNγ). Specifically, TNFα and IFNγ concentrations increased (P<0.001) in response to LPS challenge. Furthermore, concentrations of TNFα and IFNγ were decreased in (P≤0.02) in Cont steers compared to OmniGen-AF steers. These data suggest that OmniGen-AF supplementation served to prime the immune system prior to the LPS challenge, allowing for an enhanced response to LPS challenge.
Keywords: cattle, immune response, OmniGen-AF