PS3-28. Effects of a Yeast-based Additive on Growth, Rumen Fermentation, Immunity and Inflammation of Recently Weaned Brangus Steers.

Abstract This experiment evaluated the effects of a yeastbased additive on growth, rumen fermentation, immunity, and inflammation of Brangus steers during preconditioning. Seventy-two steers (BW = 266 ± 30.4 kg) were assigned to 1 of 2 treatments (4 pastures per treatment; 9 steers/pasture): 1) Control (no yeast) or 2) Yeast [7 g/steer daily of a yeast-based additive top-dressed onto dried distillers grains (DDG); RYeast40, ICC Brazil, São Paulo, Brazil]. All steers received bermudagrass hay ad libitum and DDG at 0.3% BW/day. A lipopolysaccharide (LPS) challenge was conducted on day 63 to measure inflammation and immune responses. Body weight was collected on days 0, 28, and 63; rumen fluid on days 0 and 56; and blood samples on days 0, 28, and 63 (0 and 4 hours post-LPS), and day 64 (24 hours post-LPS). Rectal temperature was collected at 0, 4, and 24 hours post-LPS, and respiration rate and sickness behavior score at 0, 1, 2, 3, 4, 5, 6, and 24 hours post-LPS. Pasture was considered the experimental unit, and data were analyzed as repeated-measures data using the MIXED procedures in SAS. Treatments did not affect (P ≥ 0.74) growth but tended (P = 0.09) to affect rumen fermentation, as Yeast steers tended (P = 0.09) to have greater concentrations of isobutyrate and isovalerate. Yeast did not affect (P ≥ 0.39) rumen fluid pH or other volatile fatty acids. Yeast steers tended (P = 0.10) to have greater serum insulin on day 63 (0 h), had greater (P < 0.01) serum non-esterified fatty acids on day 64 (24 h post-LPS), and had lower (P = 0.05) serum creatinine. Yeast did not affect (P ≥ 0.12) serum concentrations of insulin-like growth factor-1, cortisol, or other serum biochemistry variables. Yeast also did not affect (P ≥ 0.12) rectal temperature, respiration rate, or sickness behavior score after the LPS challenge. Following the LPS challenge, Yeast steers had lower (P < 0.01) serum interleukin-13, tended to have lower (P = 0.10) interleukin-1 F5, had lower (P = 0.04) monokine induced by interferon-γ at 24 h post-LPS, and had greater (P = 0.05) macrophage inflammatory protein-1β at 0 and 4 h post-LPS. Thus, yeast supplementation did not alter growth performance but modulated rumen fermentation and systemic metabolism. The additive attenuated inflammatory cytokine production and enhanced early innate immune activation following the LPS challenge, indicating reduced inflammation and a more efficient immune response during preconditioning of steers consuming a forage-based diet.