Role of tannin-rich tropical legumes in methane mitigation and rumen fermentation efficiency: A systematic literature review

Nevyani Asikin¹, Fitriani², Yuliani Suparmin² and Muhammad Ridla³

¹ Department of Nutrition and Feed Technology, Faculty of Animal Science, Agricultural State Polytechnic of Pangkajene Kepulauan, Pangkep 90655, Indonesia
nevyaniasikin@polipangkep.ac.id
² Department of Livestock Agribusiness, Faculty of Animal Science, Agricultural State Polytechnic of Pangkajene Kepulauan, Pangkep 90655, Indonesia
³ Department of Animal Nutrition and Feed Technology, Faculty of Animal Science, IPB University, Bogor 16680, Indonesia

Abstract

Enteric methane emissions from ruminants contribute substantially to global greenhouse gas accumulation. Tropical legumes containing tannins have emerged as promising natural feed additives that can mitigate methane production while modulating rumen fermentation. This systematic literature review evaluated the effects of different tannin concentrations in tropical legumes on methane mitigation, nutrient digestibility, rumen fermentation characteristics and microbial responses in ruminants. Relevant studies published between 2010 and 2026 were systematically retrieved from Scopus, Web of Science, PubMed and Google Scholar databases following PRISMA guidelines. The findings demonstrated that tannin concentration, tannin structure, forage species and rumen microbial interactions strongly influenced methane mitigation efficacy. Low tannin levels (<2% DM) produced minimal methane reduction, whereas high tannin concentrations (>5% DM) substantially suppressed methane production but frequently impaired digestibility and fermentation efficiency. Moderate tannin concentrations (2-5% DM), particularly condensed tannins, consistently produced the most balanced responses by reducing methane emissions by 15-40% while maintaining acceptable volatile fatty acid production and nutrient utilization. Methane suppression was primarily associated with reductions in methanogenic archaea and protozoal populations alongside increased propionate production.

Keywords: methane emissions, protozoa ruminants, tannins, tropical legumes

Introduction

Enteric methane (CH₄) emissions from ruminants represent a major environmental challenge because methane possesses a global warming potential substantially greater than carbon dioxide. In addition to contributing to greenhouse gas accumulation, methane production also reflects a loss of dietary energy that could otherwise support animal productivity (Kú-Vera et al 2020). Consequently, nutritional strategies capable of reducing methane emissions without impairing rumen fermentation efficiency have become an important research priority in sustainable ruminant production systems (Ridla et al 2023; Ridla et al 2025)

Among the proposed mitigation strategies, tropical legumes containing tannins have received considerable attention due to their natural antimethanogenic properties. Tannins are polyphenolic secondary metabolites broadly classified into condensed tannins (CT) and hydrolysable tannins (HT), both of which can alter rumen microbial ecology and fermentation pathways (Haque 2018; Verma et al 2024a). Several tropical legumes, including Leucaena leucocephala, Gliricidia sepium, Flemingia macrophylla, Calliandra calothyrsus  and Desmodium spp., contain varying tannin concentrations that influence methane production and nutrient utilization differently (Molina-Botero et al 2019; Baihaqi et al 2023).

Previous studies have demonstrated that tannins reduce methane through multiple mechanisms, including direct inhibition of methanogenic archaea, suppression of rumen protozoa, reduction of hydrogen availability and modification of volatile fatty acid (VFA) profiles toward greater propionate production (Asikin et al 2018; Patra 2016; Beck and Gregorini 2021). Condensed tannins are particularly effective because they can disrupt protozoa–methanogen symbiosis and limit substrate degradation required for methanogenesis (Fagundes et al 2020; Susanto et al 2024). However, the antimethanogenic response is highly dependent on tannin concentration, molecular structure and dietary inclusion level.

Low tannin concentrations (<2% DM) generally exert limited effects on methane reduction because microbial inhibition remains insufficient to substantially alter rumen fermentation pathways. Conversely, excessive tannin concentrations (>5% DM) may reduce feed intake, nutrient digestibility, ammonia production and fibrolytic bacterial activity due to strong tannin–protein and tannin–fiber complex formation (Min et al 2020; Kemboi et al 2023). Therefore, medium tannin levels (2–5% DM) are often considered optimal because they may simultaneously suppress methane production while maintaining acceptable rumen fermentation efficiency and nutrient utilization (Narváez-Herrera et al 2023).

Although numerous studies have investigated tannin-rich tropical legumes, findings remain inconsistent due to variations in tannin structure, experimental design, animal species and fermentation conditions. Moreover, many previous reviews primarily focused on methane mitigation alone without comprehensively evaluating the balance between methane suppression and rumen fermentation performance. Understanding this balance is essential because excessive fermentation inhibition may negatively affect animal productivity and long-term sustainability.

Therefore, this systematic literature review aimed to evaluate the effects of different tannin levels in tropical legumes on enteric methane production and rumen fermentation efficiency. The review specifically synthesized evidence regarding methane reduction, volatile fatty acid production, ammonia concentration, digestibility, protozoal populations and microbial responses to identify optimal tannin inclusion levels that maximize environmental benefits while maintaining efficient rumen

Material and method

Data source and screening

This study employed a systematic literature review (SLR) design to evaluate the effects of tannin levels in tropical legumes on methane mitigation and rumen fermentation efficiency in ruminants. The review was conducted between January and March 2026 following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses PRISMA guidelines (Figure 1) to ensure transparency and methodological rigor throughout the review process (Page et al 2021; Moher et al 2015). The research framework was developed using the PICO (Population, Intervention, Comparison, Outcome) approach (Table 1) to define the study's scope and objectives (Richardson et al 1995).

Figure 1. PRISMA flow diagram of literature search and study selection for tannin-containing tropical legumes on rumen fermentation, methane emissions and digestibility in ruminants

A comprehensive literature search was conducted using Scopus, Web of Science, PubMed and Google Scholar databases. Articles published between 2010 and 2026 were included in the review. The search strategy combined Boolean operators and keywords related to tannins, tropical legumes, methane emissions and rumen fermentation parameters. The search terms used were: (“tannin*” OR “condensed tannin*” OR “hydrolysable tannin*”) AND (“tropical legumes” OR Leucaena OR Gliricidia OR Calliandra OR Desmodium) AND (“methane” OR “CH4”) AND (“rumen fermentation” OR “digestibility” OR “volatile fatty acids”).

Two independent reviewers screened titles, abstracts and full texts. Disagreements were resolved through discussion with a third reviewer. Data extraction was conducted using a standardized Microsoft Excel form. Extracted variables included tannin type, tannin concentration, methane reduction, volatile fatty acid profile, ammonia concentration, digestibility and microbial responses. The inclusion and exclusion criteria were established before the screening process to ensure consistency and relevance of selected studies (Table 2).

Data analysis

Study quality was evaluated using a modified methodological scoring system adapted from Pace et al (2012). Due to substantial heterogeneity among studies regarding animal species, tannin structure and experimental design, data were synthesized qualitatively rather than through meta-analysis. Studies were grouped by tannin concentration and type to identify consistent patterns associated with methane mitigation and rumen fermentation efficiency.

Results and discussion

The present systematic review demonstrates that tannin-rich tropical legumes possess considerable potential as natural methane-mitigating feed resources in ruminant production systems. However, as summarized in Tables 3 and 4, the effectiveness of these legumes was strongly influenced by tannin concentration, tannin structure, forage species and rumen microbial interactions (Kú-Vera et al 2020; Beck & Gregorini 2021). Across the evaluated studies, condensed tannins consistently exhibited stronger antimethanogenic activity than hydrolysable tannins, particularly in Leucaena leucocephala, Leucaena diversifolia, Acacia cyanophylla and Calliandra calothyrsus. The reductions in methane production were commonly associated with decreased protozoal populations, suppression of methanogenic archaea and shifts in volatile fatty acid profiles toward increased propionate production.

The synthesis presented in Tables 3 and 4 clearly demonstrates a dose-dependent relationship between tannin concentration and methane mitigation efficiency. Low tannin concentrations (<2% DM), represented mainly by Gliricidia sepium, generally produced only minimal methane suppression because microbial inhibition remained insufficient to substantially alter methanogenic pathways (Souza et al 2025; Vastolo et al 2025). As indicated in Table 4, methane reduction at this concentration was typically below 10%, while digestibility, NH₃-N concentration and total VFA production remained relatively stable. These findings indicate that low tannin concentrations preserve rumen fermentation stability but provide limited environmental benefits.

In contrast, moderate tannin concentrations (2–5% DM) produced the most biologically balanced outcomes between methane mitigation and rumen fermentation efficiency. As summarized in Table 3, legumes such as Leucaena leucocephala, Leucaena diversifolia, Desmodium spp. and Acacia cyanophylla consistently reduced methane emissions by approximately 15-40% while maintaining acceptable digestibility and fermentation characteristics. Similarly, Table 4 demonstrates that moderate tannin inclusion increased propionate production, reduced acetate:propionate ratios and suppressed protozoal populations without causing severe inhibition of fibrolytic bacteria. These findings support previous reports indicating that moderate condensed tannin concentrations selectively suppress methanogens while maintaining overall microbial fermentation activity (Beck and Gregorini, 2021; Duarte et al 2024).

The reductions in protozoal populations observed in Table 3 appear particularly important because rumen protozoa are closely associated with hydrogen production and methanogen symbiosis (Islam and Lee 2019). Several tropical legumes presented in Table 3, including Leucaena diversifolia and Acacia cyanophylla, simultaneously reduced protozoal abundance and methanogenic archaea populations. These findings support the hypothesis that tannins indirectly reduce methane synthesis through disruption of protozoa–methanogen interactions (Fagundes et al 2020; Susanto et al 2024). Furthermore, the increase in propionate production observed in moderate tannin treatments suggests the activation of alternative hydrogen sink pathways, thereby reducing hydrogen availability for methane synthesis (Molina-Botero et al 2019; Phesatcha et al 2020).

As further summarized in Table 3, tannin structure strongly influenced antimethanogenic efficacy. Condensed tannins generally exerted stronger methane suppression than hydrolysable tannins because of their greater protein-binding affinity and microbial membrane-disrupting properties (Patra et al 2017; Naumann et al 2018). For example, Acacia cyanophylla and Calliandra calothyrsus, both rich in condensed tannins, achieved methane reductions exceeding 35%. In contrast, hydrolysable tannins from Acacia nilotica produced moderate methane suppression but also exhibited greater risks of antimicrobial toxicity at elevated concentrations because hydrolysis releases absorbable phenolic metabolites (Lozano et al 2017; Verma et al., 2024b). Therefore, both tannin concentration and molecular structure are critical determinants of ruminal biological responses.

Although high tannin concentrations (>5% DM) generated the greatest methane reductions, the results summarized in Tables 3 and 4 demonstrate that these benefits were frequently accompanied by substantial anti-nutritional effects. Tropical legumes such as Flemingia macrophylla , Calliandra calothyrsus and Acacia mearnsii markedly reduced methane production but simultaneously decreased digestibility, NH₃-N concentration, fiber degradation and total VFA production (Huyen et al 2016; Min et al 2020; Cherdthong 2024). As indicated in Table 4, excessive tannin concentrations strongly suppressed cellulolytic bacteria and fermentation activity, suggesting that methane reduction at high tannin levels partly reflected depressed fermentation rather than selective methanogen inhibition alone. Excessive tannin inclusion likely promoted the formation of stable tannin–protein and tannin–fiber complexes that reduced microbial accessibility to nutrients (Kemboi et al 2023; Zhao et al 2025).

Another important finding presented in Table 3 involves the synergistic interactions between tannins and other phytochemicals such as saponins, flavonoids and catechins. Mixed phytochemical extracts, particularly Uncaria gambirextract and tannin–saponin combinations, demonstrated enhanced methane reduction while maintaining fermentation stability (Pazla et al 2024; Pazla et al 2025). As summarized in Table 3, these combinations reduced methane emissions while maintaining digestibility and stabilizing VFA production. Such synergistic effects may provide promising opportunities for the development of multifunctional phytogenic feed additives capable of improving both environmental sustainability and nutrient utilization efficiency (Jayanegara et al 2020; Sinz et al 2019).

Despite the promising findings summarized in Tables 3 and 4, substantial variability among studies remains an important limitation. Differences in tannin quantification methods, forage maturity, animal species, diet composition, adaptation periods and experimental methodologies contributed to inconsistent responses across studies (Tedeschi et al 2021; Vargas-Ortiz et al 2022). Furthermore, many studies relied primarily on short-term in vitro incubation systems that may not fully represent long-term rumen adaptation under practical livestock feeding conditions (Verma et al 2022; Melesse et al 2017).

The synthesis presented in Tables 3 and 4 indicates that moderate condensed tannin inclusion levels (2-5% DM) from tropical legumes provide the most biologically balanced strategy for enteric methane mitigation. This concentration range consistently reduced methane production while maintaining nutrient digestibility, fermentation stability and microbial efficiency. These findings support the strategic utilization of tannin-rich tropical legumes as sustainable dietary interventions for environmentally friendly ruminant production systems.

Conclusion

This review demonstrates that tannin-rich tropical legumes effectively mitigate enteric methane while modulating rumen fermentation, with efficacy strongly influenced by tannin concentration and structure. Moderate condensed tannin levels (2–5% DM), particularly from Leucaena leucocephala , Desmodium spp. and related tropical legumes, provided the most balanced outcomes by reducing methane emissions without severely impairing digestibility or volatile fatty acid production. Conversely, tannin concentrations exceeding 5% DM caused anti-nutritional effects that reduced nutrient utilization and fermentation efficiency.

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