Hydrogen-rich water 400ppb as a potential strategy for improving ruminant nutrition and mitigating methane emissions.

The objective of this study was to evaluate the effects of different concentrations of hydrogen-rich water (HRW) on in vitro rumen fermentation characteristics and the dynamics of bacterial communities. The experiment included four treatment groups: a control (CON) and hydrogen-rich water (HRW) at 200, 400, and 800 ppb. Each group was analyzed at 12-hour (h) and 48-hour (h) time points with five replicates, totaling 40 samples. The experimental results highlighted the HRW_800ppb group as the top production in terms of gas production and CH₄ content. In contrast, the HRW_200ppb group exhibited significantly lower methane levels at both 12 h and 48 h (P < 0.05). Regarding rumen fermentation, the HRW_400ppb group significantly increased the levels of ammonia nitrogen (NH₃-N) and microbial crude protein (MCP) at 12 h fermentation, but reduced the dry matter degradation rate (P < 0.05). After 48 h, the HRW_400ppb group had highest MCP content (P < 0.05), but no significant differences in NH₃-N and dry matter degradation rate compared with the CON group (P > 0.05). Although HRW did not significantly benefit the synthesis of total volatile fatty acids (TVFA) and individual VFA, the HRW_800ppb group significantly increased the ratio of acetate to propionate (P < 0.05). Based on CH₄ emissions and MCP synthesis, we selected the HRW_400ppb group for subsequent bacterial community analysis. Bacterial community analysis showed that at 12 h, compared with the CON group, the Bacterial community analysis revealed that the HRW_400ppb group had significant increases in the Simpson index, Firmicutes, Streptococcus, Schwartzia, Prevotellaceae_YAB2003_group, and Oribacterium, and decreases in Prevotella, Ruminobacter, Succinivibrio, unclassified_Succinivibrionaceae, and Prevotellaceae_UCG-003 (P < 0.05). At 48 h, the Prevotellaceae_YAB2003_group and Oribacterium abundances continued to rise significantly, while Rikenellaceae_RC9_gut_group and Succiniclasticum abundances fell in the HRW_400ppb group (P < 0.05). Correlation analysis indicated a negative link between CH₄ and Streptococcus, and a positive correlation between the abundance of Rikenellaceae_RC9_gut_group and CH₄. Collectively, these results indicate that HRW can modulate rumen fermentation and microbial community structure to reduce methane emissions without significantly affecting VFA synthesis, highlighting its potential as drinking water for enhancing ruminant nutrition and mitigating the environmental impact of livestock farming.