PS13-19. Dietary Supplementation of a Blend of Probiotics and Prebiotics Alters the Plasma Metabolome and Improves Growth Performance in Newly Weaned Beef Steers During the Receiving Period.

Abstract The feedlot receiving period is a critical phase in beef cattle production characterized by nutritional, environmental, and immunological stressors that can impair growth performance and metabolic homeostasis. Microbial additives containing a blend of probiotics and prebiotics are increasingly used as non-antibiotic strategies to support health and performance during this period; however, host-level metabolic mechanisms underlying their effects remain poorly defined. The objective of this study was to evaluate the effects of dietary supplementation with a microbial additive containing live Saccharomyces cerevisiae and fermentation products of S. cerevisiae, Enterococcus lactis, Bacillus licheniformis, and Bacillus subtilis on the plasma metabolome of newly weaned beef steers using ^1H-nuclear magnetic resonance (NMR)–based metabolomics. Eighty newly weaned crossbred beef steers (206 ± 12 kg body weight) were assigned to receive either a control diet (CON; n = 40) or the same diet supplemented with the microbial additive (SYNB; 28 g/steer/d; n = 40) for 21 d, followed by a 14-d withdrawal period. Plasma samples were collected on d 0, 21, 28, and 35 and analyzed by 1H-NMR. Multivariate analyses were conducted using partial least squares discriminant analysis (PLS-DA), and univariate metabolite concentrations at d 21 were analyzed using mixed models with baseline adjustment. Dietary SYNB supplementation increased final body weight and average daily gain without affecting dry matter intake (P ≤ 0.01). Multivariate analysis revealed treatment-associated separation of plasma metabolomic profiles at d 21, with separation persisting through d 35. At d 21, SYNB-fed steers exhibited greater plasma concentrations of amino acids including arginine, ornithine, lysine, threonine, and valine, as well as carnitine, glycerol, malonate, and propylene glycol, whereas concentrations of ketone bodies and oxoglutarate were reduced (VIP > 1.0; P ≤ 0.10). Pathway enrichment analysis indicated enrichment of amino acid metabolism, central carbon metabolism, antioxidant-related pathways, and the tricarboxylic acid cycle. Several metabolic pathways remained enriched following SYNB withdrawal. These results indicate that SYNB supplementation is associated with alterations in plasma metabolome, which may indicate improved nutrient utilization and energy balance during the feedlot receiving period.