73. Feeding a Bacillus-based Probiotic to Beef Heifers During Stress Challenges: Effects on Feed Intake, Immune, and Metabolic Responses

Abstract Three experiments evaluated the effects of a Bacillus-based probiotic on feed intake, immune, and metabolic responses of beef heifers exposed to different stress challenges. Sixteen Angus-influenced yearling heifers were used. For all experiments (35 d each), treatments included hay and corn-based concentrate with (BAC; n = 8) or without (CON; n = 8) 3 g/head daily of the Bacillus-based probiotic. Heifers received vaccination against bovine respiratory pathogens in Exp. 1 or a lipopolysaccharide injection (LPS; 0.5 μg/kg of body weight; Escherichia coli 0111:B4) in Exp. 2, and were transported for 24-h in Exp. 3. Hay intake was measured daily across all experiments. Rectal temperature and blood samples were collected prior to and up to 21 d after each challenge. In Exp. 1, no treatment effects were observed (P ≥ 0.18) for feed intake or plasma concentrations of antibodies against vaccine antigens. The CON heifers had greater rectal temperature (P ≤ 0.05) at 8 and 12 h, and greater (P = 0.05) plasma tumor necrosis factor alpha (TNFa) concentration 6 h post-vaccine (treatment × hour; P = 0.09). In Exp. 2, hay intake was greater (P ≤ 0.05) in BAC during the 5-d period post-LPS (treatment × day; P = 0.01). Heifers receiving CON had greater (P ≤ 0.05) rectal temperature at 18, 48, and 60 h, greater (P ≤ 0.05) plasma cortisol concentration at 4, 6 and 8 h, greater (P < 0.01) plasma haptoglobin concentration from 120 to 168 h, and greater (P ≤ 0.05) plasma concentration of lipopolysaccharide binding protein at 48, 60, and 72 h post-LPS (treatment × hour; P ≤ 0.10). Mean plasma TNFa concentration tended (P = 0.08) to be less, whereas mean plasma concentrations of aspartate aminotransferase, lactate, and non-esterified fatty acids were less (P ≤ 0.05) in BAC heifers post-LPS. In whole blood samples, BAC had less (P ≤ 0.03) mRNA expression of TNFa at 2 h, tryptophan hydroxylase-1 (TH1) at 6 h, and glutathione peroxidase (GPx) and superoxide dismutase-1 at 4 h post-LPS. In Exp. 3, no treatment effects were detected (P ≥ 0.18) for feed intake, immune and metabolic responses, besides transient differences (P ≤ 0.04) in plasma glucose and β-hydroxybutyrate, and whole blood mRNA expression of GPx and TH1 (treatment × hour; P ≤ 0.05). Feeding a Bacillus-based probiotic alleviated inflammatory responses of beef heifers upon a vaccine or LPS challenge, improved feed intake and metabolic responses post-LPS, whereas no major benefits were observed upon the 24-h transport