PSV-20 The Effect of Bacillus Spp. Supplementation on Performance and Immune Function of Heifers Grazing Tall Fescue Pastures

Abstract

Abstract Probiotics are purported to improve gastrointestinal tract health across a variety of species. Thus, we evaluated the effects of supplementing a blend of Bacillus spp. on performance and immune function in immature beef cattle. Crossbred heifers (n = 192) were stratified by initial body weight (196 ± 15.4 kg) and randomly assigned to 1 of 24 pastures (1.8 ha each) of Kentucky 31 tall fescue. Heifers were offered 2.84 kg daily of a commodity feed blend and the supplement contained either no probiotic (CON) or of Bacillus spp. (BAC). Bacillus spp. was offered at 3 grams per head per day. Heifers were weighed on consecutive days on d 0 and 1, along with d 84 and 85 to establish initial and final body weight. Interim weights were taken every 28 d. A humoral response to chicken egg albumin (OVA) was established following a subcutaneous injection with OVA. To assess heifers’ immune responses, plasma was taken from two heifers per pasture on d 1, 15, 29, 43, and 57. Plasma samples were measured for the presence of anti-OVA IgG, proinflammatory cytokines, anti-inflammatory cytokines, and chemokines. There were no trt*day interactions (P ≥ 0.30) for plasma response variables. Concentrations of pro-inflammatory cytokines IL-1α and IFN-γ decreased (P ≤ 0.01) in heifers supplemented with BAC. The anti-inflammatory cytokine IL-1 F5 decreased (P = 0.02) with BAC supplementation. Chemokines MIG and MIP-1β also decreased (P ≤ 0.03) with BAC supplementation. Heifers fed BAC tended to display (P = 0.09) greater titers of anti-OVA IgG than the control. Body weight and average daily gain did not differ (P ≥ 0.53) throughout the experiment. Under the conditions of this experiment, heifers supplemented with Bacillus spp. demonstrated modulated immune responses.