Dietary supplementation of resveratrol alters rumen microbiome and reduces urinary trimethylamine/trimethylamine N-oxide excretion in dairy cows.

Trimethylamine (TMA) is a major product of ruminal choline metabolism. Understanding the microbial pathways associated with TMA formation may provide opportunities to improve rumen fermentation efficiency and animal productivity; however, effective strategies to regulate rumen TMA production remain poorly understood. In this study, in vitro and in vivo experiments were combined to investigate the effects of resveratrol on rumen TMA production and urinary excretion in dairy cows. In vitro rumen fermentation was conducted with 4 resveratrol doses (0, 0.5, 5, and 50 mmol/L). Concentrations of TMA were significantly lower in the 5 and 50 mmol/L resveratrol treatments compared with the control (0 mmol/L). The in vivo experiment was conducted using 36 mid-lactation Holstein cows with an average days in milk (DIM) of 171 ± 7 d and an average parity of 3.2 ± 0.4. The experiment lasted for 5 weeks, consisting of a 1-week adaptation period followed by a 4-week experimental period. Cows were blocked according to parity, milk yield, and days in milk and then randomly assigned to CON (basal diet), RES2.4 (basal diet + 2.4 g resveratrol/cow/day), and RES4.8 (basal diet + 4.8 g resveratrol/cow/day). The total concentrations of TMA and trimethylamine N-oxide (TMAO) in plasma and urine were reduced in cows in the RES4.8 group. Resveratrol did not affect dry matter intake, apparent nutrient digestibility, and milk performance, but it altered rumen fermentation parameters. Resveratrol also increased serum globulin and glutathione peroxidase levels and reduced serum IL-6, malondialdehyde, and superoxide dismutase. Metagenomic analysis showed that resveratrol shifted the structure of bacterial and archaeal communities but did not affect those of protozoa and fungi. The relative abundance of Prevotella was significantly lower in the RES4.8 group, whereas Eubacterium_S and the archaeal orders Methanobacteriales, Methanomicrobiales, and Methanococcales were higher. Functional profiling showed that resveratrol did not affect the overall composition of carbohydrate-active enzymes but decreased the abundance of pathways related to oxidative phosphorylation, the tricarboxylic acid (TCA) cycle, terpenoid backbone biosynthesis, lipopolysaccharide synthesis, and phenylpropanoid biosynthesis. Collectively, these findings provide new insights into the mechanisms underlying resveratrol-mediated regulation of rumen function and host TMA/TMAO metabolism.