Fecal metabolome in Nelore bulls fed pre- and post-feedlot diets.

Nutrition is a critical factor in feedlot systems, directly influencing animal growth and production efficiency. Moreover, dietary variations, particularly the transition from fibrous to non-fibrous carbohydrates, can significantly alter metabolic processes. Metabolomics can elucidate how dietary shifts influence bovine performance, offering valuable insights that could optimize feeding strategies. The aim of this study was to identify and quantify fecal metabolites in Nelore bulls (Bos taurus indicus) subjected to different diets during the pre- and post-feedlot. Thus, 21 Nelore bulls were subjected to a diet rich in fibrous carbohydrates in the pre-feedlot phase. Subsequently, these animals were fed a diet rich in non-fibrous carbohydrates in the post-feedlot phase. Fecal samples were collected directly from the rectal ampulla of each bovine at the end of each phase. The fecal metabolites were extracted, and their spectra were obtained through Hydrogen Nuclear Magnetic Resonance (1H NMR) analysis. A total of 63 metabolites were detected across all samples, with 57 present in the pre-feedlot and 55 in the post-feedlot phase, reflecting diet-specific metabolic signatures. Eight metabolites were exclusively identified in the pre-feedlot phase (caprylate, fumarate, desaminotyrosine, gamma-glutamyl phenylalanine, 2-phenylpropionate, NADH, thymidine, and pantothenate), while six compounds were present only in the post-feedlot phase (acetamide, 2-oxoglutarate, uracil, xanthine, trimethylamine, and dimethyl sulfone). The major metabolites, including acetate, propionate, butyrate, ethanol, valerate, isobutyrate, glucose and isovalerate, showed the highest concentrations in both pre- and post-feedlot phases and together represented around 93% of the total fecal metabolite’s concentration. Forty metabolites showed differential abundance between the experimental groups (P ≤ 0.05). Multivariate analyses, including PCA and PLS-DA, confirmed clear separation of the fecal metabolome between phases and highlighted acetate, propionate, and butyrate as key contributors to variance. Additionally, six pathways exhibited an impact value greater than 0.2 and P ≤ 0.05, being: (1) phenylalanine, tyrosine, and tryptophan biosynthesis; (2) glycine, serine, and threonine metabolism; (3) pyruvate metabolism; (4) glycerolipid metabolism; (5) citrate cycle (TCA cycle); (6) histidine metabolism. These results demonstrate that the diets provided during pre- and post-feedlot phases influenced the fecal metabolome of Nelore cattle, altering metabolite concentrations and associated metabolic pathways. These changes highlight potential biomarkers for nutritional interventions aimed at optimizing performance.