Dietary green tea residue improves growth and antioxidant capacity via rumen microbiota and glutathione modulation in finishing beef cattle

BACKGROUND: Green tea residue (GTR) is an abundant by-product rich in polyphenols. This study aimed to investigate the effects of GTR on growth performance, rumen microbiota, and systemic metabolism in finishing beef cattle. RESULTS: Forty-five 18‑month‑old finishing Angus steers with an average initial body weight of 474.44 ± 14.03 kg (mean ± SD) were individually housed and randomly assigned to three dietary treatments (n = 15 per group) using stratified randomization by initial body weight: control group (CG group, 150 g rice straw), low-dose GTR group (LG group, 75 g rice straw +75 g GTR), and high-dose GTR group (HG group, 150 g GTR). The feeding trial lasted 70 d with a 10-day adaptation period. To elucidate the regulatory mechanisms of GTR on beef cattle growth, we thoroughly assessed growth performance, nutrient digestibility, ruminal fermentation parameters, conducted bacterial 16S rRNA sequencing, analysed plasma biochemical and antioxidant markers, and executed an untargeted plasma metabolomic analysis. The LG group tended to increase average daily gain (ADG). Meanwhile, the LG group exhibited elevated plasma concentrations of β-hydroxybutyrate and glucose, increased activities of superoxide dismutase and glutathione S-transferase, an increased glutathione (GSH)/glutathione disulfide (GSSG) ratio, and reduced GSSG content. GTR treatment decreased reactive oxygen species and oxidative stress index. Furthermore, dietary GTR significantly modified the rumen microbial community structure, enriching Xylanibacter and Prevotellaceae_UCG-003, while reducing the abundance of Rikenellaceae_RC9_gut_group. Plasma metabolomics revealed that GTR treatment enriched GSH Metabolism and the Pentose Phosphate Pathway. Notably, gamma-glutamylcysteine was identified as a key mediator of the association between Xylanibacter and ADG in fattening beef cattle supplemented with GTR. CONCLUSIONS: Dietary supplementation with 75 g/steer/d GTR improved growth performance and systemic antioxidant capacity in finishing beef cattle by modulating the rumen microbiota and activating the glutathione system. GTR represents a promising functional feed additive that simultaneously valorizes tea by‑products and enhances livestock productivity.