The role of dosage and regional origin of Gambir (Uncaria gambir) leaf extract in enhancing rumen fermentation and suppressing methane emissions

A study was conducted to determine the effects of extracts of Uncaria gambir leaves from 8 regions in Indonesia on characteristics of in vitro rumen fermentation, nutrient disappearance, and methane (CH₄) production. Results showed that the parts of the plant from the Traju and Talang Maur regions have higher contents of catechins and tannins, which are important bioactive compounds to alter rumen microbial ecology. Dry matter and crude protein disappearance and total volatile fatty acid concentrations were improved significantly by supplementation at 2% of dietary dry matter (DM). Most importantly, this treatment also resulted in a significant decrease in protozoa numbers and methane emissions without affecting rumen pH and fermentation consistency. The combination of catechins, tannins, and saponins in the gambir extracts had a synergistic effect on inhibiting microbial activity and methane production, likely due to combined effects on hydrogen sink efficiency and microbial inhibition. These results confirm the potential of regional Uncaria gambir extracts, especially from Traju and Talang Maur, as natural rumen modifiers. Their use at the appropriate dose can enhance the fermentation profile and assist in methane mitigation approaches, thereby achieving a more sustainable and climate-resilient ruminant production system. This in vitro study evaluated the effects of Uncaria gambir leaf extracts from eight distinct Indonesian regions, applied at three inclusion levels, on nutrient disappearance, rumen microbial fermentation profile, enteric methane (CH₄) emissions, protozoa populations, and microbial biomass. The in vitro experiment utilized a randomized block design in an 8 × 3 factorial arrangement, involving extracts originating from Sutera, Pangkalan, Langgai, Traju, Simpang Kapuk, Maek, Tolang, and Talang Maur at supplementation levels of 0.5%, 1%, and 2% of dietary dry matter (DM). Extracts from Traju and Talang Maur at the 2% inclusion level, characterized by higher tannin and catechin contents (71.37% and 71.51%, respectively), showed the most promising results: they enhanced dry matter disappearance (69.90%, P<0.05), NH₃ concentration (16.02 mg/100 mL, P<0.05), and VFA concentration (158.00 mM, P<0.05) while reducing CH₄ production to 6.62 mL/g DM, representing a 47% decrease relative to the lowest-performing treatment (P < 0.05). Increasing the level of gambir supplementation was positively correlated with improved nutrient disappearance, higher NH₃ and VFA concentrations, and lower CH₄ production, without disrupting rumen pH (range: 6.82–7.06) or microbial biomass. These findings underscore the role of region-specific phytochemical profiles in modulating rumen microbial dynamics. Given Indonesia’s leading position as a gambir producer, this study provides strong evidence supporting the use of Uncaria gambir as a natural, locally available additive to improve rumen efficiency and mitigate methane emissions in sustainable livestock systems.