Mitigating Strategies For Enteric Methane Emissions In Ruminants: An Overview On Sustainable Alternatives

Global warming is considered as one of the most critical and concerning issue worldwide. The phenomenon of global warming, primarily driven by the human induced accumulation of greenhouse gases in the atmosphere, poses a major threat to our planet and its ecosystems (Bajoria et al., 2024). Due to increase in greenhouse gas emissions, the global surface temperature has increased by 1.1 °C between 2011 and 2020 (Bilgili et al., 2024). The dominant green house gases (GHG) produced by anthropogenic activity are Carbon Dioxide (CO₂), Nitrous Oxide (N₂O) and Methane (CH₄) (Yin et al., 2025). Methane (CH₄), produced during enteric fermentation, have higher global warming potential (28–34 times) than that of CO₂ (Huang et al., 2026). The growth in global methane emissions mostly occurred after 1950 and was mainly contributed by livestock sector (Zhang et al., 2022). The livestock production contributes 12% of global methane emissions, as methane is a normal product of ruminant digestion (Symeon et al., 2025). However, the contribution of enteric methane emissions to global greenhouse gases is relatively low (Güler, 2024). Cattle are the primary contributor of methane emissions compared to other ruminants like sheep and goat because of their size and quantity (Broucek et al., 2014). In ruminant, the enteric methane emissions also reflect a loss of up to 12% of feed's energy that would instead be used for animal productivity (Malyugina et al., 2025). In ruminants, the digestion of feed stuff is accomplished by a complex microbial ecosystem constituting bacteria, archaea, protozoa, and fungi and transforms it into highly valuable products for human consumption (Tardiolo et al., 2025). During ruminal fermentation, various gases are produced, primarily hydrogen and carbon dioxide (Zheng et al., 2026). Inside the rumen, methanogens utilize these two gases for methane production, which eructated out into the atmosphere (Hosen et al., 2025). Feed additives are commonly used in ruminant nutrition for their many beneficial effects like animal growth promoter, toxin binder, breakdown of anti-nutritional factors and reducing methane emission (Dhanasekaran et al., 2020). Plant secondary metabolites are low-molecular-weight organic compounds found in plants; mainly include phenolics, terpenoids, alkaloids and flavonoids (Wu et al., 2025). In recent years, many studies suggested that plant secondary metabolites like saponins, tannins and essential oil, have the ability to manipulate rumen fermentation in a positive way, thus can be used as natural feed additives for improving ruminant production systems and reducing methane emission (Kumar et al., 2025; Holik et al., 2025; Nasir et al., 2025). This review focuses to evaluate the best ways to decrease enteric methane emissions by the use of environment friendly additives of plants origins such as saponins, tannins and essential oils in animal nutrition.

Effect of Feeding Saponins on Enteric Methane Emission

Methanogenesis is the main pathway of hydrogen disposal during the feed fermentation in side rumen. This methane production may be decreased by an inhibition of hydrogen production or by a shift in hydrogen allocation. Both these mechanisms lead to a reduction of H₂ availability for methanogenic archaea (Guyader et al., 2015). Many studies have revealed the positive effects of the plant extracts such as saponins and tannins in mitigating methane emissions (Jayanegara, et al., 2020). Saponins are naturally occurring plants secondary metabolites that are important in human and animal nutrition. The structure of saponins consists of a hydrophilic sugar moiety linked to a lipophilic aglycone, making them amphiphilic in nature. Saponins exhibit surface-active properties, creating stable foams and forming complexes with other molecules (Timilsena et al., 2023). Both in-vitro and in-vivo studies revealed that saponin from different plant sources have the potential to improve animal production and reduce enteric methane production. However, the beneficial effect of saponins supplementation depends upon the dose and type of substrate used. In an in-vitro study, methane production was reduced up to  39, 24 and 25%, when tea saponins were used at level of 0.6% in three substrates having different concentrate to roughage. In the same experiment, the reduction in methane production was observed by 17, 7 and 14% when tea seeds powder was used as a raw source of saponin in the same level (Kumar et al., 2025). This study also revealed that beneficial results were obtained when crude saponin mixture was used as compare to tea seed powder which was added as a raw source of saponin in all three substrates. In an another in vitro study, decrease in methane production was observed when tea seed saponin was added at levels of 0.0%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% and 1.0% of substrate using low forage diet (forage: concentrate, 30:70), a medium forage diet (forage: concentrate , 50:50) and a high forage diet (forage: concentrate, 70:30) (Jadhav et al., 2018). Tea saponin levels directly reduced enteric methane production by reducing ruminal microbial populations (Yanza et al., 2023). The above studies suggested that tea seed saponins and tea seeds have the potential to modify the rumen fermentation pattern by reducing methane and ammonia release, thus beneficial for improving the animal growth and nutrient utilization. Another in vitro study revealed maximum reduction in methane production up to 29% and protozoa concentration up to 51%, when increasing dosage of the tea saponin extracts were added in the substrate using in vitro batch culture incubations using bovine rumen contents as inoculum and a cereal mixture as substrate (Guyader et al., 2017). The Delonix regia seed meal, which is high in tannins and saponins, was when added at levels of 0, 3.3, 5.0, 6.7, 8.3, 10, 11.7, 13.3, 15.0 and 16.7 mg in a substrate having 70:30 roughage and concentrate ratio (in-vitro), methane production was reduced with increasing levels of Delonix regia seed meal in the diet (P < 0.05) (Supapong et al., 2017). One in-vitro study was conducted to assess the effect of a composite plant extract (CPE) rich in polyphenolics and saponins on ruminal fermentation and methanogenesis, using seeds of Dolichos biflorus (horse gram), root of Asparagus racemosus (shatavari), bark of Amoora rohituka (rohitaka), and peel of Punica granatum (pomegranate). The results showed decrease in methane and ammonia concentration and increase in dry matter digestibility with increasing doses of composite plant extract (Shilwant et al., 2023). Aspergillus niger β-glucosidase-modified alfalfa saponins when were used in an in-vitro rumen fermentation study, the Methanogen abundance reduced by 20.10–44.93%, and general anaerobic fungi reduced by 34.22–44.66%. This in vitro findings revealed that enzyme-treated alfalfa saponins modulates rumen fermentation pattern through methane mitigation and increased nutrient utilization, making it a sustainable feed additive strategy for livestock (Zhang et al., 2025). Decrease in Methane yield was observed due to presence of plants secondary metabolites in quinoa plant, when different strains of silage quinoa were used in an in-vitro study. These findings suggest that feeding quinoa silage to ruminants has the potential to reduce greenhouse gas emissions (Ge et al., 2025). Soapnut fruits have high saponin content about 10% of fruits. Soapnut powder was when added @ 0, 1, 2, up to 8% on DM basis with substrate in 100ml in vitro syringe, the in-vitro methane gas production decreased by 22.16 and 15.79% with 1 and 2% of soapnut (Rathod et al., 2024). The Yucca schidigera extract (YSE) and Quillaja saponaria extract have a suppressing effect on rumen methane production due to antiprotozoal action (Pen et al., 2006). However, one study revealed that the increasing Yucca schidigera saponin extract inclusion increased the propionate proportion in vitro but there was no reduction observed in methane production (Trotta et al., 2023). Saponins may decrease methane production due to defaunation effect and/or directly by decreasing the activities and numbers of methanogens (Patra and Saxena, 2009). Results of above studied showed that dietary supplementation of saponin decreased enteric methane emission in ruminants for both low and high levels of saponin in the diet. Hence it is recommended that the saponin is effective to reduce enteric methane emission from ruminants provided that its level of use should not exceed 0.5% of DM (Ridla et al., 2021).

Effect of Feeding Tannins on Enteric Methane Emission

Tannins (hydrolysable and condensed tannin) are polyphenolic compounds of relatively high molecular weight with the ability to form complexes with proteins due to the presence of a large number of phenolic hydroxyl groups in their structure (Patra and Saxena, 2011). They are widely distributed in forage trees, shrubs and legumes, cereals and grains. Tannins found in various feed stuffs can affect microbial activity, fermentation processes, protein degradation, and methane production in the rumen (Holik et al., 2025). One study was conducted by feeding tannin-containing hays to heifers and mature beef cows and its effects on enteric methane (CH4) emissions and nitrogen (N) excretion were evaluated. The results suggest that tannin-containing hays have the potential to reduce urinary urea nitrogen excretion, increase nitrogen retention, and reduce enteric methane emissions from beef cattle (Stewart et al., 2019). In cows, diet supplemented with chestnut, quebracho, and seaweed tannins (@ 200 g/day significantly reduced the total protozoan count, as well as the abundance of main protozoan groups (Holotrichs and Entodiniomorphids) in the rumen (P < 0.05) (Holik et al., 2025). These findings suggested that dietary supplementation of tannins affects ruminal protozoan composition and the rumen microbial community, and have anti-methanogenic potential. The study suggested that dietary tannins suppress rumen methane production by reducing the population of protozoan. When tannic acid supplemented @ 6.5, 13.0 or 26.0 g/kg DM in four adult Simmental male cattle, there was decrease in (p < 0.01) methane production by 11.1%, 14.7% and 33.6%, respectively (Yang et al., 2017). In an another study, four legumes with different concentrations of condensed tannins (CT) were tested: alfalfa (ALF); birdsfoot trefoil (BFT); crown vetch (CV); and sericea lespedeza (SL). The CT concentrations were 3, 21, 38 and 76 g/kg of DM for ALF, BFT, CV, and SL diets, respectively. Total CH4 production (mg of CH4/d) was lower (P < 0.001) in the sericea lespedeza supplemented diet in comparison to other 3 diets (Roca-Fernández et al., 2020). Another study was conducted using different legumes rich in condensed tannins (CT) in vitro and their effect was observed on methane emissions and rumen microbiota in beef cattle. The results revealed that Leucaena leucocephala, Desmodium paniculatum and Lespedeza procumbens have the potential to suppress rumen methane production (Fagundes et al., 2020). Inclusion of 80% of Leucaena leucocephala in the diet of heifers fed low-quality tropical forages has the ability to reduce up to 61.3% enteric methane emission without affecting Dry Matter Intake and protozoa population in rumen liquor (Piñeiro-Vázquez et al., 2017). One study was conducted to evaluate the long-term effects of feeding hydrolyzable tannin (HT) with or without condensed tannin (CT) on animal performance, rumen fermentation and methane production in beef cattle fed a high-forage diet. This study concluded that a combination of HT and CT at a concentration of 1.5% dietary DM tended to decrease methane emissions without affecting animal performance (Aboagye et al., 2018). In sheep, the inclusion of soybean oil or soybean oil plus tannins reduced methane production and decreased rumen protozoa compared to control treatment (P < 0.01) (Lima et al., 2019). The use of low levels of tannin extract from Acacia mearnsii have shown to reduce rumen protozoa and methane production and is considered as a potential option to manipulate rumen fermentation in Nellore and Holstein cattle (Perna Junior et al., 2023). One study aimed to compare in vitro rumen fermentation characteristics and to evaluate the effects of condensed tannins (CT) on methane production in dairy cattle (Bos taurus taurus), zebu beef cattle (Bos taurus indicus), water buffaloes (Bubalus bubalis), sheep (Ovis aries) and goats (Capra hircus) using Acacia (Acacia molissima) tannin extract and fed similar diets. The results showed that bovines emitted more methane than small ruminants as measured on a degraded organic matter basis. Condensed tannins have greater effects in large ruminants than in small ruminants (Bueno et al., 2015). A study was carried out to investigated how low-dose tannic acid (T), tea polyphenols (TP), and their combination (T+TP; 50:50) affects rumen microbiota and its function in Holstein cows. Compared with the control group, all diets supplemented with additives significantly reduced enteric methane production (13.68% for T, 11.40% for TP, and 10.89% for T+TP) and significantly increased milk protein yield (Zhao et al., 2025). Tannin‐containing tropical tree leaves, Autocarpus integrifolis, Azardirachta indica and Ficus bengalensis, when included in optimum doses in the ruminant diets, suppress methanogenesis (Bhatta et al., 2015). The addition of quebracho tannins extract (QTE) at 2 or 3% of dry matter ration can decrease methane production up to 29 and 41%, respectively, without significantly compromising feed intake and nutrients digestibility in cattle fed low-quality Pennisetum purpureum grass. (Piñeiro-Vázquez et al., 2018). In an invitro study, tannin extracts were isolated from four different forage species: birdsfoot trefoil (Lotus corniculatus), sulla (Hedysarum coronarium), big trefoil (Lotus pedunculatus), and salad burnet (Sanguisorba minor) decreased the methane (CH₄) production compared to the control group. The highest CH₄ reduction (15%, at 30 g/kg DM) was observed from sulla and big trefoil extracts indicating importance of tannins in animal nutrition (Verma et al., 2024). The cell membrane, cell wall, and glycocalyx of methanogen contain adhesin protein. It is possible that condensed tannins bind to this adhesin or parts of the cell wall, preventing the formation of methanogen-protozoan complexes and reducing interspecies H₂ transfer and thus reducing the methane emission (Ng et al., 2016).

Effect of Feeding Essential Oils on Enteric Methane Emission

Essential oils are blends of secondary metabolites obtained from the plant by a type of distillation, such as hydro distillation, steam distillation, or microwave assisted dry distillation (Sadgrove et al., 2015). Terpenoids (including monoterpenoids and sesquiterpenoids) and phenylpropanoids are the most important bioactive compounds in essential oils (Calsamiglia et al., 2007). The natural feed additives like garlic oil (GO), garlic powder (GP), allicin (ALL), yucca schidigera plant extract (Yucca), and an essential oil blend (EO), have shown positives effects as rumen microbiome modifiers (Hodge et al., 2025). Essential oils from Garlic and cinnamon have shown to reduced methane emissions; but they can also reduce in vitro dry matter digestibility (Molho-Ortiz et al., 2022). In an in-vitro study, two optimal blends of cinnamon and peppermint oils (80:20) and anise and clove oils (80:20) significantly reduced total gas and methane production compared to controls, with the cinnamon–peppermint blend achieving the highest methane reduction. These results suggested the potential use of essential oil blends as effective, sustainable alternatives to conventional feed additives in animal production (Nasir et al., 2025). Four essential oils (EO) isolated from Achillea santolina, Artemisia judaica, Schinus terebinthifolius and Mentha microphylla, and supplemented at four levels (0, 25, 50 and 75 μl) to 75 ml of buffered rumen fluid plus 0.5 g of substrate in an in vitro study. The main components of the EO were piperitone (49.1%) and camphor (34.5%) in A. judaica, 16-dimethyl 15-cyclooactdaiene (60.5%) in A. santolina, piperitone oxide (46.7%) and cis-piperitone oxide (28%) in M. microphylla, and γ-muurolene (45.3%) and α-thujene (16.0%) in S. terebinthifolius. The essential oils from Achillea santolina and Artemisia judaica, and Mentha microphylla inhibited the methane production and reduced the protozoa count along with NH₃-N concentration (Abdallah Sallam et al., 2011). Essential oils from oregano and white thyme, when were tested in four doses (0, 50, 250 and 500 mg/L) in an in-vitro study revealed that they have the potential to modify ruminal fermentation and suppress rumen methane production without negative effects on feed digestibility, suggesting it as an alternatives to ionophores for methane reduction in beef cattle (Benetel et al., 2022). Combination of Essential oils from Ceylon cinnamon, dill seeds, eucalyptus, and probably others, at low concentrations may be a pragmatic approach to reduce methane emission and nitrogen excretion from ruminant without negatively affecting feed digestion or fermentation (Cobellis et al., 2016). Supplementation of 1 g/day of blend of essential oils daily in the ration of dairy cattle reduces methane production on absolute terms (l/d) and decreases the amount of methane production per unit of dry matter consumed, and the effect is sustained over time without affecting feed intake or milking performance (Bach et al., 2023). When basal diet was supplemented with 200 mg and 400 mg microencapsulated blend of essential oils (MBEO)/kg dietary DM in 9 sheep, there was reduction in methane emissions  (24.5 and 27.6 l/kg digestible organic matter (DOM), respectively) treatments as compared to the control group (38.2 l/kg DOM) (Soltan et al., 2018). The effects of increasing concentrations (1.0, 1.5 and 2.0 g/L) of oregano (Origanum vulgare L.) and rosemary (Rosmarinus officinalis L.) essentials oil have also shown promising effects on ruminal gas emissions when tested in vitro. The maximum reduction of methane production was observed upto 72% and 9% with oregano and rosemary EO, respectively (Cobellis et al., 2015). The supplementation of 0.5% orange essential oil (OEO) reduced methane emissions (g/day) by 12% without affecting the dry matter intake in heifers fed bermudagrass hay as a basal diet (Jiménez-Ocampo et al., 2022). The supplementation of Essential oil blends (garlic, lemongrass, cumin, lavender, and nutmeg) and fumaric acid have shown to be an effective way to reduce greenhouse gas emission and enhance total volatile fatty acids. Compared with the control, the addition of essential oil blends (100 µL) have shown to decrease methane production by 86.4%, and fumaric acid (3% of total mixed ration) by 90.8% in an in vitro study using inoculum from three rumen-cannulated Black Angus beef cows (Alabi et al., 2023). Sage, pine, and clove essential oils (300, 600, and 900 mg/L) have shown positive effects on methane production and in vitro ruminal fermentation parameters, in an in vitro study using rumen inoculum from three mature Dalagh ewes (Bokharaeian et al., 2023). Effects of 6 essential oils from garlic/, thyme, clove, orange peel, mint, and cinnamon in different doses (100, 200 and 300 ppm) were studied on in vitro rumen methane reduction and in vitro digestibility using in vitro gas production technique. All essential oils reported to have highest in-vitro methane reduction potential (MRP doses) at 300 ppm dose without any negative effect on in vitro Digestibility (Rofiq et al., 2021). Essential oils from Origanum vulgare  and Thymus vulgaris (3 mL per kg of concentrate) supplementation have no effect on in vivo methane emissions and rumen parameters in Nellore beef cattle (Benetel et al., 2024).  It is well reported that the effect of Essential oils on methane production may either due to toxicity to methanogens or reduction in H₂ production due to decreased acetate and butyrate production (i.e. reduced fibre digestion) (Kumar et al., 2014). Based on the above studies, it is concluded that, a combination of several Essential oils at low doses or a combination of Essential oils with other antimethanogenic agents is an effective alternative in mitigating methane emission from ruminants (Patra and Yu, 2012). 

CONCLUSION

This review article highlighted the beneficial effects of various phytogenic feed additives due to their ability to change the rumen microbial ecology and reducing methane production. These photogenic substances are derived from trees, shrubs, and legumes. In this review most of the studies conducted are in vitro experiments; however, to understand the efficiency of these phytogenic substances and their effects on methanogenesis, and animal performance, in vivo studies are needed to validate the results. These studies not only protect our environment from global warming but also enhance the farmer’s income due to the organic nature of finished products.

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