PSI-22 Rumen fluid metabolites influenced by endophyte-infected tall fescue seed and red clover isoflavones in beef steers

Fescue toxicosis causes substantial financial losses to the beef industry due to its negative effects on reproduction, growth and feed efficiency. Recent research has demonstrated that the negative effects of fescue toxicosis may be mitigated by supplementation of red clover isoflavones. To determine impacts on the ruminal environment, the objective of this study was to evaluate the effect of red clover isoflavones and endophyte-infected tall fescue on ruminal metabolites. Thirty-six Angus steers weighing 250±20 kg were randomly assigned to treatments in a 2×2 factorial arrangement, consisting of endophyte-free or endophyte-infected tall fescue seed with or without red clover isoflavones. For the 21d trial, steers were provided a basal diet supplemented with fescue seed targeting a minimum of 0.011 mg × kg of BW−1 × d−1 of total alkaloids. A total of 943 mg isoflavones were administered daily via bolus. Following the trial, 50mL of rumen fluid was collected via orogastric tubing. Untargeted metabolomic analysis was performed using an Exactive Plus Orbitrap MS, and 10µL sample was introduced using electrospray ionization into the Dionex UltiMate 3000 UPLC system. Peaks were identified in MAVEN, then normalized and analyzed in MetaboAnalyst 4.0, and 106 known metabolites were identified. Differences in seed type × isoflavone were analyzed by one-way ANOVA and main effects were analyzed by t-test. A total of 11 metabolites differed based on seed type × isoflavone treatment group (P ≤ 0.05), 11 differed by seed type (P ≤ 0.5), and seven differed by isoflavone treatment (P ≤ 0.05), namely amino acids or intermediates of amino acid metabolism. Methane (P = 0.03) and sulfur (P = 0.03) metabolism pathways were both impacted by isoflavone treatment, whereas 20 metabolic pathways were impacted as a result of differences in seed type (P ≤ 0.05). The rumen metabolome appears to be more affected by seed type, but a longer trial will likely result in more profound impacts.