Type: Review
Modern nutritional approaches to mitigating enteric methane emissions in ruminants: A review
Sabrin Abdelrahman Morshedy 1,*
1. Fish and Animal Production Department, Faculty of Agriculture (Saba Basha), Alexandria University, Alexandria, Egypt
Abstract: Sustainable livestock production increased public concern towards reducing greenhouse gases. The emission of enteric methane from ruminants, if not well managed, contributes to a significant loss of energy consumed and a marked environmental challenge. Methane has <80 times higher global warming potential than CO2. Enteric methane contributes by <40% of agricultural emissions and 13-19% of global methane emissions. Furthermore, the increased demand for animal protein sources, especially in developing countries, highlights the pressure on greenhouse gas emissions. Therefore, the search for a methane mitigating strategy is a continuous series and a hot topic in animal nutrition laboratories. There are several mitigating nutritional strategies with varying mitigating potentials from 10 to 90% associated with or without digestion or growth complications. These solutions include the use of new ingredients such as insect meal, modulating the quality of food, the inclusion of lipids, and increased concentrate: roughage ration, which decreased CH4 approximately by 18%, 30%, 6% and 50% in the best situations. Furthermore, feed additives have considerable effects on CH4 emissions by inhibiting methanogenesis or competing with substrates for methanogens, such as nanoengineered or nanoencapsulated materials, CH4 inhibitors (statins, bromochloromethan, and 3-NOP) that could inhibit CH4 production by 90%. Several phytobiotic feed additives, including tannins, saponins, and essential oils, have moderate CH4 inhibition effect up to 30%. Seaweed was reported to have nearly complete inhibition of CH4 of the Asparagopsis, Ascophyllum, Dictyota and Rhodophyta genes in vitro or in vivo evaluation. However, the application of these solutions still faces some barriers, including cost, availability, efficacy across production systems, and potential impacts on animal productivity. This review evaluates the mechanisms, effectiveness, and nutritional implications of these nutritional strategies, with particular attention to their applicability in different ruminant production systems (in vivo and in vitro models) for more sustainable production.
Keywords: Enteric CH4; nutritional strategies; CH4 inhibitors; insect meal; nanotechnology; feed additives.
Article Info.
Submitted: 1/5/2025; Revised: 23/5/2025; Accepted:25/5/2025; Online: 27/5/2025
Cite as: Morshedy, S. A. (2025) Modern nutritional approaches to mitigating enteric methane emissions in ruminants: A review. Animal Reports, 1: 41-59. https://doi.org/10.64636/ar.10
1 Introduction
With the growth of the population and increased nutritional awareness, the demand for animal protein products (meat, milk, and processed animal products) is increasing. This increase is associated with serious environmental impacts and triggers public health and environmental concerns related to greenhouse gases produced by ruminants (Ban & Guan, 2021). Worldwide efforts have been paid of trying to control the increase in greenhouse gas production and increased atmospheric temperature above 1.5 ℃ by 20250 to maintain global warming at a safe level (Reisinger et al., 2025). This commitment needs to reach zero greenhouse gases emissions globally by 2050, which means an equilibrium between emitted gases and the recovery of these gases by the environment (Matthews & Wynes, 2022).
Ruminants have a unique digestive system that adapts to utilized low quality feed and forage and digests complex fiber sources during fermentation process to produce easy digested substrates and new nutrients, including volatile fatty acids (VFA), vitamins, proteins, ….. etc. (Owens & Basalan, 2016). This process performed by a group of anerobic microbes in a complex ecosystem including bacteria, protozoa, and fungi that have adaptability, interactions, and symbiotic relationship (Castillo-González et al., 2014). The rumen is a suitable environment for these microorganisms to grow and reproduce and get energy from the animal feed, at the same time it facilitates roughage and low-quality grass digestion and conversion to highly nutrients in their microbial body mass that can be used by the host finally (Wanapat et al., 2013). On the other hand, the fermentation process produces some by-products, such as carbon dioxide and H₂, with the latter used by Methanogens to produce CH4 (Owens & Basalan, 2016).
Ruminants consider the main CH4 producer in the agriculture sectors, whereas they contribute by <40% of CH4 emission from agriculture greenhouse gases (Dillon et al., 2021) and 13-19% of the global CH4 emissions (Liu & WB., 2008). CH4 has 86 times global warming potential that of CO₂ during the last 20 years (IPCC, 2021). Furthermore, CH4 causes a significant energy loss averaged 8-12% of total consumed feed, which consequently causes significant economic loss (Johnson KA & DE., 1995). CH4 emissions also represent part of energy losses during ruminant farming. On average, approximately 8 to 12% of the energy consumed in feed is wasted in the form of CH4 emissions (Johnson & Johnson, 1995). Few numbers of the largest meat and dairy companies (35) produced 14% of total livestock greenhouse gases emissions and currently they have to acquire the possible strategies to decrease this emissions (Leahy et al., 2020). Figure 1 showed the contribution of different main sectors to CH4 emission. It showed that the agriculture sector represents the second source of CH4 after the energy sector.
Fig. 1. Contribution of the main sectors to CH4 (%) emission (Ritchie, 2020; Dillon et al., 2021).
The attempts to reduce CH4 emission from ruminants are the worldwide focus of animal nutrition scientists. Hundreds of attempts have been conducted, including management, genetics, and nutritional strategies (chemical and antimicrobial compounds) to modify the microbial structure or the fermentation process to reduce CH4 production and enhance energetic efficiency (Owens & Basalan, 2016). The review aims to provide a comprehensive resource for researchers, nutritionists, and policymakers seeking novel nutritional-based solutions to alleviate or mitigate CH4 emission from livestock and overcome these sustainability challenges.
2 Methane production in the rumen and Methanogenesis
Understanding CH4 production in ruminants requires examination of the rumen's complex microbial ecosystem (Patra et al., 2017). The responsible microorganisms for CH4 production in rumen is methanogens, which are several species of anaerobic organisms (120 species) that can utilize carbon dioxide and hydrogen to produce CH4. The methanogens usually grow at pH range of 6.0–8.0 and can utilized hydrogen, formate, methanol, methylamine, acetate, etc. as a substrate (Sirohi et al., 2010; Cersosimo & Wright, 2015). The rumen methanogens community structure differs from ruminant species to others and also feed type, in Mandya sheep fed on straw and concentrate diet Bacteroidetes and Firmicutes represent 82% of the bacterial community and Methanobacteriales constituted of 13% of the community, while Archaea acount 2.5% of the ruminal microbiota (Malik et al., 2022).
The CH4 production process begins in the rumen by breaking down plant polysaccharides by fiber-digesting bacteria (e.g., Ruminococcus spp.) producing H₂ as a byproduct (Gleason, 2021). This H₂ is then utilized by methanogenic archaea (primarily methanobrevibacter spp.) to reduce CO₂ to CH₄ through the hydrogenotrophic pathway (Liu et al., 2017). In addition, rumen ciliate protozoa play a crucial role by hosting Methanogens in symbiotic relationships, accounting for up to 37% of total Methanogenesis (Gleason, 2021).
Several dietary factors significantly influence the CH4 production process, high-fiber diets promote acetate production (a major H₂ source), while starch-rich diets favor propionate formation, which acts as an H₂ sink (Li et al., 2022; Chiariotti, 2023). Animal-related factors also contribute, with breed differences and the production stage affecting emission rates (Ghassemi Nejad et al., 2024; Muetzel et al., 2024). Recent advances in microbial genomics have revealed substantial diversity in rumen methanogen populations, suggesting potential for targeted microbial interventions (Ghassemi Nejad et al., 2024). The ratio of acetate to propionate in rumen fermentation serves as a key indicator of CH4 production potential, with higher acetate: propionate ratios typically associated with greater CH₄ emissions (Morgavi et al., 2010; Vanhatalo & Halmemies-Beauchet-Filleau, 2020).
3 Dietary Strategies for CH4 Mitigation
3.1 Insects as novel feed ingredients
Recently, the use of edible insects as a feedstuff is increasing, where it introducing nutritious and cost-efficient feed ingredients (Hong & Kim, 2022). Its impacts on rumen fermentation and CH4 production need to be extensively addressed. Ahmed et al. (2021) reported that substitution of 25% of soyabean with Gryllus bimaculatus and Brachytrupes portentosus meal significantly decreased CH4 production by 18% and 16%, respectively.
In addition, in male beef cattle, cricket (G. bimaculatus) meal using as a 100% substitution levels of soyabean meal significant increased VFA, and propionate concentrations, with significant decrease of CH4 production and protozoal populations (Phesatcha et al., 2023). Eight full-fat insect meals were examined in comparison with conventional plant protein sources by in vitro experiment. The used insect meal markedly reduced total gas production, CH4 emission, total VFA, ammonia level, and organic matter disappearance compared to plant proteins (Renna et al., 2022).
Black soldier fly larva oil has been used in in vitro study up to 6% in 40:60 roughage to concentrate ratio. The results indicated that 4% is the suitable addition level with significant low level CH4 production and suitable digestibility coefficients (Prachumchai & Cherdthong, 2023). The modulation effects of insect meal or oil on ruminal fermentation could be attributed to its chitin, fat, and protein contents, and the high level of unsaturated fatty acids that could inhibit rumen fermentation (Renna et al., 2022).
3.2 Forage quality and management
One of the main strategies to mitigate CH4 production is considering the quality of dietary forage. Legumes like alfalfa and clover typically produce 15-20% lower CH4 yields (g CH₄/kg DMI) than grasses due to their lower fiber content and faster rumen passage rates (Hatew, 2015). Bannink et al. (2016) reported that CH4 emission intensity changed in dairy cattle fed grass herbage and grass silage by 5.6% to 7.3% of gross energy intake and 27.4 to 36.9 g CH4/kg digested OM, and 19.7 to 24.6 g CH4/kg dry matter, respectively. Sheep (Romney ewe hoggets) fed alfalfa silage substituted with increasing levels of corn silage (25, 50, 75 or 100%) or corn grain (25, 50 or 65% rolled corn grain) on a DM basis at a fixed DMI level (2% of BW). The results revealed that emission of CH4/DMI increased with increasing substitution levels up to 50% with both corn silage and corn grain then decreased gradually but not than that of 100% alfalfa silage (Jonker et al., 2016).
In growing beef cattle, the effect of vegetative and mature fresh pasture forage and supplementation with maize silage or palm kernel expeller on CH4 production (g/day) and yield (g/kg dry matter intake; DMI) was studied in growing beef cattle. No clear differences were observed in CH4 production between feeding of vegetative or mature pasture. However, using 100% maize silage increased the CH4 yield by 23.80%. Also, supplementation with maize silage increased CH4 production by 10% than cattle fed mature pasture only or supplemented with palm kernel expeller (Jonker et al., 2015). These studies revealed that improving forage quality represents one of the most accessible CH4 mitigation strategies for pasture-based systems (Bannink et al., 2016; Jonker et al., 2016; Macome et al., 2017).
Furthermore, pasture management could also affect CH4 production. Feeding dairy cows with whole-plant corn silage at different maturity levels (25-40% dry matter) showed that increasing harvest maturity level reduced CH4 production linearly without negatively affecting cow performance (Hatew et al., 2016). In another study, forage maturity at harvest significantly impacts CH4 emission potential, with early cutting forages (vegetative stage) reducing emissions by up to 30% compared to mature forages (Ramin & Huhtanen, 2013). Therefore, strategic grazing management, including rotational systems that maintain forage at optimal growth stages, can further enhance these benefits while improving overall system productivity. Furthermore, increasing starch levels in the diet affect CH4 production in cows fed diets total mixed ration of (60% grass silage and 40% concentrate on DM basis). In situ incubation of starch showed that CH4 production was decreased in fast than slow and in high starch–based diets than low starch-based diet (Hatew, Podesta, et al., 2015). However, trade-offs exist, as higher-quality forages may require more intensive management and potentially higher production costs. In tropical systems, the introduction of tannin-rich legumes like Leucaena leucocephala has shown particular promise, reducing CH4 by 22% while improving protein supply (Animut et al., 2008).
3.3 Lipid supplementation
Lipid supplementation reduces enteric CH4 emissions primarily through the biohydrogenation of unsaturated fatty acids (UFAs) in the rumen (Bayat & Shingfield, 2012). The mechanism by which UFAs (linoleic acid (C18:2) or linolenic acid (C18:3)) can control CH4 emission is the ability of rumen bacteria to convert them into saturated fatty acids (SFAs) by incorporating hydrogen (H₂) into their carbon chains (Yang et al., 2024). This process competitively reduces the availability of H₂ for Methanogenic archaea, thereby suppressing CH4 (CH₄) production (Caro et al., 2016). Furthermore, this mechanism differs depending on fat source, in steers grazing tallgrass-prairie alone or supplemented with whole cottonseed, bypass fat, or a supplement containing soybean oil. All fat supplemented groups had lower CH4 production than the control group. This effect may have resulted from reduced ADF digestibility (Beck et al., 2019). Also, in grazing steers fed 1% linseed oil supplementation reduced CH4 emissions by 38% when expressed in mg/d/kg BW (Carvalho et al., 2016). Additionally, certain lipids (e.g., medium-chain fatty acids like lauric acid, C12:0) exhibit direct antimicrobial effects on Methanogens by disrupting their cell membranes (Soliva et al., 2004). Studies indicate that for every 1% increase in dietary lipid content (up to 6–7% of dry matter intake, DMI), CH4 yield (g CH₄/kg DMI) decreases by 5.6% on average (Martin et al., 2010). On the other hand, Cross-bred Aberdeen Angus steers feed increasing oil levels only tended to reduce in CH4. However, the combination with nitrate supplementation could enhance the decrease of CH4 production (Duthie et al., 2018).
In sheep, supplementation with fat had high suppression effects on CH4 production based on meta analysis (Patra, 2014). Dietary increasing levels of macadamia cake (4.5%, 8.5%, and 14% on a dry matter basis) as a high nutritional value ingredients with reach source of lipids reducing daily production of enteric CH4 without negatively affect the nutrient digestibility and ruminal fermentation up to inclusion levels of 14% (Takahashi et al., 2024). However, fat can be possible mitigation methods to CH4 emission, some implication could be experienced with high fat inclusion rate, including reduce microbial attachment, altering fibrolytic bacteria, fiber degradation (Toral et al., 2009; Shinkai et al., 2012).
3.4 Concentrate feeding and starch-rich diets
Rumen microorganisms enable to digest the cellulose rich feed stuff (roughage) to VFA that can be used by the animal as a source of energy and finally converted to meat and milk, however a by-products of this process were elaborated, including hydrogen and CO2 which can be utilized by Methanogens to produces CH4 (Nadeem & Sufyan, 2005). Several previous studies evaluated the potential of manipulating the roughage-to-concentrate ratio to reduce the formation of gases. However, increasing non-fiber roughage or concentrate (starch) directed the rumen fermentation process toward propionate production rather than acetate (Wang et al., 2018). Propionate considers electron acceptors, in another words, acts as a hydrogen sink and competing with methanogens for available hydrogen (Wang et al., 2023).
The level of starch inclusion, fermentation rate (slow, medium, and rapid) or its form (native and gelatinized) significantly affect CH4 production in cow or in vivo studies. Whereas high inclusion rate, rapid and gelatinized starch reduced CH4 production (Hatew, Cone, et al., 2015). The effect could also be due to the bypass of 30% of starch to the small intestine without fermentation avoiding methanogenesis in the rumen (Harmon et al., 2004).
Wang et al. (2018) reported in an in vitro experiment that reducing neutral detergent fiber content from 24.0 to 15.8% with maintaining other dietary ingredients at the same ration causes a 14.06% decrease in CH4 production. In another study, increasing starch in cows diets increased total rumen VFA levels, decreased acetate production without differences in rumen pH, or ruminal CH4 production (Darabighane et al., 2021).
Furthermore, forage-to-concentrate ratio positively affects the fermentation process in ruminants and subsequent CH4 emissions. The increase in forage: concentrate from 68:32 to 39:61 respectively, significantly reduced CH4 emissions by 27.2 and13.8% in Holsteins cows and Jerseys cows, respectively (Olijhoek et al., 2018). In grazing Jersey cows on ryegrass pasture, increasing concentrate supplementation levels (0, 4, and 8 kg/cow/day) linearly decreased enteric CH4 production without affecting VFA concentrations and ruminal pH (Van Wyngaard et al., 2018). In in vitro study using rumen fluid inoculum grazing cows feed on Italian rye grass and different concentrate levels (2, 5, and 8 kg/animal/day). The use of a high concentrate level increased total gas and propionate with decreased CH4 production (Kim et al., 2018). CH4 emission decreased by 48% in Holestine cows fed a diet with 91% concentrate (Olijhoek et al., 2022). Recently, the effect of using agriculture by-products, including spent mushroom, hempseed cake, red and green apple pomace, coffee by-products, and distiller's dried grains with soluble at a level of 100, 200 and 300 g kg−1, the in vitro results revealed a linear decrease of gas production and CH4 emissions. The maximum percent of CH4 production was 33.6% with inclusion of 300 g kg−1 (Xue et al., 2025).
The increasing in concentrate or starch percent in the ruminal diet represents promising mitigation approaches to CH4 production, meanwhile this process could have some trade-offs such as ruminal acidosis (Elmhadi et al., 2022). Lambs fed diets with 25% starch or higher decreased blood pH and HCO3 values with the potential risk of subacute acidosis (Şevket & KARSLI, 2024). Starch infusion in cow acclimated to high fiber diet decreased fecal pH as an indication of hindgut acidosis (Abeyta et al., 2023). Ruminal acidosis could be associated with ruminal microbial modulation and several heath complications, including rumenitis, milk fat depression, inflammation, laminitis, and liver abscesses (Elmhadi et al., 2022).
4 Feed Additives
Feed additives are widely used in commercial ruminants production systems not only improving animal health and production performance, but also to modulate ruminal microbiota to low CH4 emissions (Newbold & Rode, 2006). Several pathways were identified for controlling CH4 production by feed additives including suppressing of methanogenesis or competing with substrate for methanogens (Honan et al., 2021; Sun et al., 2021). Fig. 2 illustrated complications and mitigation strategies of methane production in rumen.
4.1 Nono-feed additives
Nanotechnology is a cutting-edge technique for mitigating CH4 emissions from ruminants. Nanoengineered materials have enhanced properties depending on the type, size, and synthesize methods, including absorption, adsorption, and cation exchange capacity (Mahler et al., 2012). These properties could increase the potential of using nano-substances in controlling enteric CH4 emissions. Zn-nanoparticles reduced the microbial population, CH4 production and hydrogen sulfide in automated gas production system during 72 hours at 500 and 1000 μg g− 1 (Sarker et al., 2018). Furthermore, in vitro gas production model, the addition of Zn oxide and nano-Zn at increasing levels (20, 40, and 60 mg Zn/kg DM) significantly decreased CH4 emissions and protozoa count at level of 20 mg normal or nano-Zn form. The increase in Zn levels (40, and 60 mg Zn/kg DM) did not add any positive effects (Riazi et al., 2019). Green-synthesized CuO and ZnO nanoparticles have been added to rumen fluid up to 20 mg/ml with using alfalfa (Medicago sativa) hay as the main substrate. Both nanoparticle significantly decreased CH4 emission, protozoa colonization, in vitro gas production, however CuO negatively affect ruminal fermentation (Palangi et al., 2024).
The nanomodified natural adsorbents also showed a high efficiency of CH4 mitigation. The use of nano-montmorillonite (MNM) coated with cetyltrimethylammonium bromide at a dose of 0.5 g / kg of DM significantly reduced CH4 emission and improved in vitro nutrient digestion (Soltan et al., 2021). Nano-zeolite was tested compared to natural zeolite in vitro and in vivo using goats on rumen fermentation. The in vitro experiment indicated that both forms of zeolite have affected CH4 emission in a linear model. In the in vivo experiment, both zeolite forms increased total short-chain fatty acids and butyrate concentrations and significantly decreased ammonia levels (El-Nile et al., 2021). Recently, urea-impregnated nano-zeolite was added to sheep diet, which significantly reduced CH4 emissions in its heat activated form and significantly increased the production of acetate, propionate, butyrate, and total VFA (Kardaya et al., 2025).
Fig. 1. Methane production complication and dietary mitigation strategies.
Nano-encapsulation technique is widely used in the field of animal nutrition to enhance animal performance, taste and texture of the diet, protecting active components and reducing wastes (Garba & Fırıncıoğlu, 2023). Furthermore, nano-encapsulated Yucca schidigera extract (0.25, 0.5, and 1 mL/g DM) was used in vitro experiments using bulls’ ruminal fluid. All supplementation significantly increased gas production and decreased CH4, CH4 conversion efficiency, CO, and H2S emissions (Botia-Carreño et al., 2024). The nano-encapsulated threonine, methionine, tryptophan, and lysine were tested on in vitro gas production experiment. The use of nano-encapsulated methionine recorded the lowest significant CH4 production and the highest metabolizable energy, while nano-encapsulated threonine reported the lowest (De Jesús et al., 2024).
4.2 CH4 inhibitors
Several statin compounds (simvastatin, atorvastatin, and rosuvastatin) were used as a CH4 inhibitor in an in vitro experiment at levels starting from 1: 100 mg/L. All tested level reduced CH4 production and the highest effective was simvastatin and the lowest was rosuvastatin (Joch et al., 2022). The metabolites of Monascus ruber (mainly lovastatin) were tested as anti-methanogenic and showed a linear decreasing effect on CH4 production (Boudra et al., 2024). Furthermore, lovastatin was examined using the rumen inoculum of sheep, goats, and cows. It showed a marked lowering effect on CH4 emission, especially in sheep rumen, more than other tested rumen. Total VFA was not affected, but acetate and valerate were decreased (Ábrego-García et al., 2024).
3-nitrooxypropanol (3-NOP) inclusion in dairy cow total mixed ration at dose of 60 mg/kg for 15 days decreased CH4 emission (26%), emission yield (27%), and emission intensity (29%), without any negative effects on feed efficiency or productive performance (Melgar et al., 2021). Van Wesemael et al. (2019) determined the effect of 3-NOP supplantation methods in dairy cows and found that inclusion in roughage or concentrates efficiently reduced CH4 production by 28 and 23%, respectively.
A 1-year 3-NOP supplementation experiment was conducted using Holstein-Friesian dairy cows to identify the long-term effects of 69.8 mg of 3-NOP / kg of DM on milk production and CH4 emission. The results indicated an overall reduction of 21% in CH4 production; however, the effect of 3-NOP decreased over time. The yields of energy and fat and protein corrected milk increased by 6.5% compared to the control (van Gastelen et al., 2024). 3-NOP is a highly specific CH4 inhibitor that inhibits the nickel enzyme methyl-coenzyme M reductase and disrupts CH4 synthesis in the rumen methanogens (Duin et al., 2016).
BromochloroCH4-cyclodextrin was also used as a dietary supplementation in steers rumen and induced an absence of Methanogenic archaeal with 4.5-times higher Lachnospiraceae (Matsui et al., 2020). A combination of chloroform and 9,10-anthraquinone was used as CH4 inhibitor in the solid diets of the young calves during the first 12 weeks and was monitored for 49 weeks of rearing. The treated animal showed nearly CH4 inhibition (90% reduction) with increasing H2 emissions also the acetate: propionate ratio decreased, meanwhile the microbial community was not affected by treatment which means that treatment affected the microbial metabolic pathways (Cristobal-Carballo et al., 2021).
Furthermore, the addition of active carbon at a level of 0.5% reduced 30-40% of CH4 emissions and 10% of CO2 production associated with decreased of Methanogenic flora by 30% and increased the nonmethanogenic species (Al-Azzawi et al., 2021). A novel activated carbon-rich mineral supplement was used to mitigate at 0 - 6% DM level in vitro experiments using Rhodes grass hay substrate and rumen fluid from Holstein-Friesian steers. The treatment inhibits CH4 production up to 29.32% without negative effects on total VFA production and DM digestibility (Tahery et al., 2025).
4.3 Phytobiotic compounds
Secondary metabolites from plants could be used to mitigate gas production. The rumen-cannulated Merino wethers fed encapsulating Acacia mearnsii tannin extract showed a reduction in CH4 production of 19% and 30% with encapsulating and crude tannin extract, respectively (Adejoro et al., 2019). The increasing in tannin in the cattle diet to 12.5 g/kg DM by including of green tea by-product significantly reduced CH4 emission without compromising animal performance (Khoa et al., 2018). In Nellore (Bos indicus) and Holstein (Bos taurus) cows fed tannin extract at increasing levels of 0. 0.5, 1, 1.5% of dry matter. The threshold for suppression of CH4 emissions was 0.72% of tannin supplementation, and the effect was significantly increased with increasing supplementation levels (Perna Junior et al., 2023).
The effect of tannin extract from different forage species was tested compared to rutin on gas and CH4 production at increasing levels (10, 20, and 30 g/kg DM). The results showed that tannin causes 15% CH4 reduction at the highest level of supplementation, while rutin did not affect its production (Verma et al., 2024). The mixture of tannin from quebracho and chestnut in individual or in combination with essential oil (EO) blends were used in vitro. The addition of tannin induced a reduction of ammonia production by 31% and CH4 emission by 15% (Foggi et al., 2022).
Effect of three essential oils (sage, pine, and clove) supplementation with increasing levels (300, 600, and 900 mg/L) on vitro ruminal fermentation characteristics was evaluated using rumen inoculum from three mature ewes. The gas and CH4 production were significantly reduced with all essential oil and the best effect was reported with clove oil (Bokharaeian et al., 2023). Furthermore, garlic, thyme, clove, orange peel, mint, and cinnamon significantly reduced CH4 and gas production in vitro at a level of 300 ppm (Rofiq et al., 2021). In non-pregnant female ewes fed dietary supplementation with essential oils blend (essential oils and polyphenols), bioflavonoids and chestnut tannins had lower CH4 production by 13% than control animals (Atzori et al., 2023). Moreover, using Pinus koraiensis cone essential oil (PEO) at a level of 1g/kg diet reduced CH4 production by 67% in vitro model based on 50:50 roughage to concentrate ratio (Choi et al., 2023).
Dietary saponin alone or in combination with nitrate and sulphate at level of 1.5% of concentrate feed significantly reduced CH4 production in calves by 11.84, 26.78, and 38% with nitrate and sulphate, or nitrate and saponin or combination with nitrate, sulphate and saponin, respectively (Yadav et al., 2021). The saponins reach Sesbania graniflora pods meal extract was used in at increasing level (0, 0.2, 0.4, and 0.6%). The results indicated a significant reduction in decreased protozoal population, CH4 emission in a dose-dependent manner (Unnawong et al., 2021). Lactating Beetal goats fed plant extract (CPE) rich in polyphenolics and saponins experienced a higher proportion of VFA and propionate with lower concentrations of acetate, CH4 and ammonia. This effect is associated with higher production performance and animal health (Shilwant et al., 2023).
4.4 Seaweeds and algae
Algae and algae extracts were investigated to control CH4 emission in vivo and in vitro models with suppression levels reaching 91% of emission. Total gas and CH4 production were significantly reduced phlorotannins extracted from seaweed Ascophyllum nodosum in a dose-dependent manner (Wang et al., 2008). An in vitro experiment was carried out to evaluate the effect of 20 tropical marine and freshwater macroalgae on gas and CH4 production using rumen fluid from cattle fed low-quality roughage. The results indicate that all examined macroalgae induced significant reduction in gas and CH4 production and the highest effective species are Dictyota and Asparagopsis with suppression of gas production by 53.2% and 61.8%, and CH4 production by 92.2% and 98.9% after 72 h, respectively (Machado et al., 2014).
Increasing dietary levels of A. taxiformis in the sheep diet reduced total VFA production and acetate levels with increasing propionate concentrations. Therefore, it was associated by 80% reduction in CH4 emission after 72 days of experiment (Maia et al., 2016). Using rumen fluid cannulated Holstein cows and supplanted with 0.5% Rhodophyta sp. extracts increased cumulative gas production with decreased CH4 production and ciliate-associated methanogens , and improved acetate/propionate ratio (Lee et al., 2017).
In dairy cattle, red seaweeds, A. armata, was used as a feed additive to mitigate CH4 production at levels of 0.5 to 1%. CH4 production was decreased by 26.4% and 67.2% at 0.5% and 1% A. armata supplementation level respectively (Breanna M Roque et al., 2019). In vitro evaluation showed a marked reduction in CH4 production by tropical macroalgae, A. taxiformis, from 38.7 mL/g DM in the control to 0.20 mL/g DM in 2% algal supplemented treatment, that represent 90% suppression effectiveness (Chagas et al., 2019). The use of red macroalgae A. taxiformis at dose of 0.5% significantly reduced CH4 production in a semi-continuous in vitro rumen system by 95% without any negative effect on other fermentation parameters. The same study suggested that A. taxiformis CH4 suppression effect could attributed to rapid metabolic alteration in rumen Methanogens to inhibit CH4 production and extended decline in methanogen abundance (Breanna Michell Roque et al., 2019). The main mode of action of seaweeds CH4 inhibition is due to the presence of bromoform compound which disrupts vitamin B₁₂-dependent enzymes in Methanogens , and blocking the final step of CH4 synthesis (Glasson et al., 2022).
5 Conclusion
This review highlighted the potential of different modern nutritional strategies to mitigate enteric methane emission. Among the reviewed strategies, insect meal as a novel feedstuff has potential methane mitigating effects. However, methane inhibitors that include feed additives (nanomaterials, statins, bromochloromethan, 3-NOP, photobiotics, and seaweed) have a promising effect in somewhat blocking methane production. As the world seeks sustainable production of animal protein, the reduction of methane could be of prime importance for producers, scientists, and policymakers to achieve the SDGs goals. Integrated approaches that combine feeding management, customized feed additives and precision feeding may offer sustainable pathways for CH4 reduction without compromising animal performance.
Sabrin A. Morshedy: Conceptualization, Investigation, Software, Methodology, Validation, Formal analysis, Writing-Original Draft, Writing-Review & Editing
Ethical approval:
Not applicable.
Informed consent:
Not applicable.
Conflict of interest statement
The authors declare no conflict of interest.
Data availability statement
The data that support the findings of this study are available from the corresponding author upon reasonable request.
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