Phenolic fraction-specific effects of tropical plants on in vitro ruminal methane production and fermentation characteristics

¹ Department of Animal Nutrition and Feed Technology, Faculty of Animal Science, IPB University, Dramaga Bogor 16680, Indonesia
² Animal Feed and Nutrition Modelling (AFENUE) Research Group, Department of Nutrition and Feed Technology, Faculty of Animal Science, IPB University, Dramaga Bogor 16680, Indonesia

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

This study evaluated how plants with different dominant phenolic fractions affect in vitro ruminai fermentation characteristics and methane production. Three phenolic-rich species were tested: Swietenia mahagoni (high condensed tannins), Clidemia hirta (high hydrolysable tannins), and Eugenia aquea (high non-tannin phenolics). Each was incubated alone or mixed with Carica papaya (CP), a low-phenolic substrate. A 24 h in vitro rumen fermentation assay was conducted to measure total gas production, organic matter digestibility, methane output, microbial population, volatile fatty acid (VFA) profiles, and ammonia concentration. Data were analyzed using two-way ANOVA followed by Duncan's test (n = 4 per treatment). Mixing phenolic-rich plants with CP significantly reduced methane emissions (P < 0.05), with CP + S. mahagoni showing the greatest reduction (18.6%). This effect was likely associated with tannin-nutrient complex formation, which modulated rumen microbial activity, supported fibre fermentation and VFA production, and limited protein degradation for ammonia synthesis (P < 0.05). The strong negative relationship between total phenols or tannins and methane output highlights the important role of phenolic compounds in regulating rumen fermentation. These findings suggest that tannin-rich plants are promising natural feed additives for mitigating enteric methane emissions in ruminants.