Application of fenugreek in ruminant feed: implications for methane emissions and productivity

Introduction

Concentrations of methane (CH₄) in the atmosphere have soared since 2007, the recent rapid rise in global CH₄ concentrations is primarily biogenic, most likely due to agriculture, according to the new data (Saunois et al., 2016). Ruminants play an important role in sustainable agriculture, among which is the transformation of renewable resources into human-edible food (Ripple et al., 2014). But their production processes also serve as a source of greenhouse gases (GHG) for various supply chain activities. One of the main ways ruminants release CH₄ is through enteral fermentation, which is the microbial fermentation of feed in the gastrointestinal tract (Thorpe, 2009). The main agricultural source of CH₄ and the third-largest source of greenhouse gas emissions, behind energy and industry, is enteral fermentation (Frank et al., 2019). Data shows that the global livestock sector contributes roughly 14.5% of all anthropogenic GHG emissions, with ruminants accounting for close to 12% of these emissions and approximately 44% of these emissions are CH₄ (Fig. 1) (Gerber et al., 2013). Ruminant GHG emissions are thought to be responsible for around US$0.679 trillion and US$13 billion in damages to the environment and human health, respectively (Goedkoop et al., 2009). Economic development and population growth will further expand human demand for meat and dairy products. By 2050, there will be a 70% increase of global food demand, which is expected to result in a 30–40% increase in agricultural emissions (Hristov et al., 2013). This runs counter to the European Council Directorate-General for Climate Action goal, which states that developed countries must reduce GHG emissions by 80–90% by 2050, compared with 1990 levels (Sanchez-Martinez, Benedetti-Fasil & Christensen, 2019). There is tremendous pressure on food production systems to meet demand while also being environmentally friendly, sustainable, and climate-smart (Hristov et al., 2013). Therefore, novel solutions and more effective CH₄ mitigation strategies are required for the sustainable development of ruminant farming (Beauchemin et al., 2020; Tseten et al., 2022).

A further challenge in reducing CH₄ emissions from the agricultural sector is the growing demand for milk and meat (Eisler et al., 2014). Ruminant livestock and their products are an important food in human nutrition, especially in less developed countries. How to find a new method that can meet the high yield of high-quality protein, control CH₄ emissions and maximize productivity (lactation, growth, immunity and other properties) under the conditions of high density and intensive culture is very vital (Tseten et al., 2022). While numerous technical alternatives are available, implementation of these interventions may be hampered by significant infrastructure and precision nutrition strategy investment costs (Tseten et al., 2022). Adding some plants that are rich in condensed tannins and saponins to feed appears to have the potential to mitigate CH₄ emissions and increase productivity due to the direct effect of diet on rumen fermentation patterns (Ku-Vera et al., 2020). Farmers may decide to employ the approach of supplementing animal feed since it has several advantages, including the promotion of growth, improvement of animal health, reduction of GHG emissions of livestock, and sustainability (Du et al., 2018). The addition of supplements to feed or diets may improve nutritional absorption and retention. Since the scientific community and the animal protein community are moving away from the use of antibiotics as growth promoters due to microbial resistance, alternatives are needed (Manyi-Loh et al., 2018). Researchers are becoming more interested in using phytogenous products as feed supplements in animal production (Adegbeye et al., 2019).

Fenugreek (Trigonella foenum-graecum L.), named Trigonella for its triangular-shaped, yellowish flowers and leaves, is an annual herb of the legume family that is native to the Mediterranean region and Indian subcontinent (Syed et al., 2020). Farmed for food, spices, animal feed, and herbal medicine, fenugreek is grown extensively in Asia, Africa, and Europe (Ahmad et al., 2016). Fenugreek is also a dryland crop, the ability of fenugreek to grow in desert regions typified by high temperatures and water scarcity makes it a good choice for future phytogenous feed additives (Wijekoon et al., 2021). Past research on fenugreek has focused on its medicinal functions and nutritional value; products derived from its seeds and leaves have been used extensively in various pharmaceuticals, nutritional products, and clinical treatments (Singh et al., 2022). Fenugreek contains a variety of chemical components, such as saponins, phenolic acid derivatives, steroids, terpenes, alkaloids, flavonoids, amino acids, and fatty acids and their derivatives (Fig. 2) (Singh et al., 2022), which have recently attracted great research interest and are considered to have the potential to mitigate CH₄ emissions of ruminants at therapeutically-effective dosages. Dey (2015) found in the simulated rumen fermentation experiment in vitro that incubation of 30 ml of buffered rumen fluid with 2 ml methanol extract of fenugreek leaves for 24 h significantly reduced the total gas and methane production. Kumar et al. (2016) has similar results. Meanwhile, fenugreek as a growth promotor, lactagogue, immunostimulant and antioxidative agent application in animal feed has been widely recognized. Adding 0.04% fenugreek in the diet can significantly improve the growth and plasma biochemical indexes, and enhance the immunity and antioxidant of juvenile blunt snout bream (Yu et al., 2019). This has also been demonstrated in animals such as chickens, rabbits and sheep (Abdel-Wareth et al., 2021; El-Tarabany et al., 2018; Paneru et al., 2022; Yang et al., 2022). Fenugreek has been used as a galactologue since ancient times in nations such as China, Egypt and Persia, owing to the role of trigonelline. It has also been demonstrated to increase lactation in animals such as mice, cattle, and sheep (Daddam et al., 2023; Muddathir, 2012; Sevrin et al., 2019). Therefore, it has the potential to be a new type of green product (Acharya, Thomas & Basu, 2008; Huang et al., 2022; Sahoo et al., 2020).

This review aims to provide insight into fenugreek in terms of enteric CH₄ mitigation efficacy, growth-promoting and lactation-promoting functions in ruminants, possible mode of action, and safety deriving data from reported research data. It could provide clear guidelines for fenugreek application, either as a feed additive or forage supplement. We believe that this article will be of interest to professionals involved in greenhouse gas mitigation, the development of novel feed products for livestock, plant secondary metabolites, and new green antibiotic alternatives.

Survey methodology

The databases of Google Scholar, Web of Science, PubMed, Scopus and Science Direct were used for the literature search. Articles with unavailable abstracts and nonpeer-reviewed were excluded. The major literature bibliography was also used to search for other connected publications. The initial keywords search was fenugreek or Trigonella foenum-graecum L. For more focused search, we added terms such as methane, rumen fermentation, growth, milk production, antioxidants, all for the sake of the ruminant. The articles that came up in the first search were then carefully reviewed by examining the abstract and scanning the entire text. The literature that conforms to the theme of this article is selected, summarized, and finally completed this article.

Fenugreek as a forage crop

Fenugreek is a bloat-free legume that serves as a medicine or functional food, as well as a fodder crop for livestock and is predominantly cultivated in Southern Europe, Asia and North Africa (Acharya, Thomas & Basu, 2008). Fenugreek has great potential as a substitute forage crop, based on seed yield, nutritional value and yearly output. Alfalfa (Medicago sativa L.) is one of the many herbaceous legumes that are currently used as high-nutrient fodder crops. The nutritional content of fenugreek for fodder is higher, or equal to that of alfalfa, at all growth stages (Islam et al., 2017). When alfalfa and fenugreek were compared as fodder for cows, there was no significant difference in the digestibility of the two feeds, however, the fenugreek-fed cows had a lower food intake, but a higher milk output than the alfalfa-fed cows (Alemu & Doepel, 2011). Fenugreek can be used for short-term rotations, because it is rich in crude protein and does not cause flatulence of ruminants, so it has the potential to be used as forage for young ruminants (Nedelkov et al., 2019). Early-harvested whole fenugreek had higher crude protein and fiber concentrations than first-flowering alfalfa, whereas the fiber content of mature fenugreek was lower than alfalfa and their crude protein contents were similar (Niu et al., 2021). Fenugreek is a desirable feed crop in the Canadian cattle sector, because it contains compounds (e.g., diosgenin) that support animal growth and it appears that cows prefer the taste of fenugreek (Harper et al., 2016).

With yields of up to 1,300 kg/hectare, fenugreek seed has the potential to be used in animal feed, however yields vary greatly depending on the variety (Basu et al., 2009). Unfortunately, genetic diversity amongst fenugreek genotypes has rarely been estimated. Fenugreek fodder yield is strongly correlated with climate, being higher in semi-arid areas and lower with frequent rainfall; fenugreek production in southern Alberta during the wet season only produces an average yield of 5.8 tons of dry matter per hectare, which may limit its viability (Mir et al., 1997). Fenugreek is a legume that fixes atmospheric nitrogen 283 kg N ha⁻¹ year⁻¹, reducing the requirement for nitrogen fertilizer for succeeding crops and boosting the growth of subsequent crops in the rotation (Zandi et al., 2015). Fenugreek is a dryland crop, which requires very little water, therefore growing it can reduce irrigation expenses, water consumption, eutrophication of surface water sources and depletion of groundwater sources (Solorio-Sánchez et al., 2014). Fenugreek can also grow adequately in slightly alkaline, or marginally saline soils, however, its ability to grow on saline soils has only been partially assessed (Ahmad et al., 2016).

Overall, fenugreek has great potential as a fodder crop, but its properties also restrict its growth and use, so more research is needed to enhance its crop yield, stability, and performance.

Fenugreek and ruminant CH₄ emissions

Secondary metabolites of fenugreek that reduce CH₄ emissions and the potential effect on biochemical pathways

Secondary metabolites of fenugreek.

Secondary metabolites are highly bioactive and have been widely used to improve rumen fermentation and also have the potential to influence the growth rate of rumen microbial populations, thereby reducing CH₄ emissions from the ruminant gut (Ku-Vera et al., 2020). The potential of tannin (Aboagye & Beauchemin, 2019; Min et al., 2020), saponin (Goel, Makkar & Becker, 2008a; Patra & Saxena, 2009), essential oil (Benchaar et al., 2008) and flavonoid compounds (Olagaray & Bradford, 2019) to mitigate CH₄ in the intestinal tract of ruminants has all been evaluated. Secondary metabolites are quite rich in fenugreek, especially in its leaves and seeds, including steroidal saponins, flavonoids, alkaloids, amino acids, phenolic acids and tannins (Table 1) (Omezzine et al., 2017). Figure 3 shows the structural diversity of the compounds isolated from fenugreek. Saponins are high molecular weight glycosides that usually occur as glycosides or polycyclic triterpenes of steroids. Saponins are structurally characterized by either a hydrophobic triterpenoid ring or a steroidal skeleton (Venkata et al., 2017). In the main components of fenugreek seeds, the content of steroidal saponins is about 6.5%. At present, dozens of saponins have been isolated from fenugreek, of which the diosgenin element dominates, which is believed to be the precursor of many sex hormones (Srinivasan, 2006). Flavonoids are polyphenols with the C6-C3-C6 skeleton, which are mainly distributed in seeds, stems and leaves, and more than 10 kinds of flavonoids have been isolated and extracted from fenugreek (Singh et al., 2022). The majority of flavonoids in fenugreek are present as complex glycosides, conjugating with carbohydrates via O- and C-glycosidic bonds, according to the phytochemical examination of the plant (Venkata et al., 2017). It displays anti-inflammatory, antioxidant, and antibacterial properties and interferes with different bactericidal agents, and has the potential to improve animal welfare (Cushnie & Lamb, 2011). Tannins are a class of water-soluble polyphenolic polymers, which have an important role in controlling parasites and regulating microorganisms (Naumann et al., 2017). Numerous significant phenolic compounds with antioxidant, anticancer, and antibacterial effects, including p-coumaric acid, caffeic acid, and chlorogenic acid, have been extracted from fenugreek (Ahmad et al., 2016).

Table 1:

Biologically active constituents of fenugreek and their pharmacological efficacy.

Active substances	Efficacy	References
Alkaloids	Hypoglycemic, antioxidant, neuroprotective, anti-migraine, antibacterial, antitumor	Zhou, Chan & Zhou (2012)
Amino Acids	Insulin stimulating activity, increasing insulin sensitivity	Ahmad et al. (2020)
Saponins	Anti-bacterial, anti-diabetes, heart protection, anti-cancer	Spandan et al., (2017)
Flavonoids	Antioxidant, anti-bacterial, hypoglycemic	Wang et al. (2019)
Phenolic acids and derivatives	Antioxidant, anti-cancer, anti-bacterial	Yoshikawa et al. (1997), Grusak (2003)
Others	Regulatory functions	Hasanzadeh et al. (2010)

DOI: 10.7717/peerj.16842/table-1

Effect of fenugreek on rumen microbiota.

Rumen microorganisms include ciliate protozoa, anaerobic fungi, anaerobic bacteria and archaea, which all contribute to rumen fermentation; 90% of CH₄ emitted from ruminants is produced by rumen microorganisms (Tapio et al., 2017). Because of the symbiotic interaction between archaea and protozoa as well as the presence of active colonies of methanogenic archaea on their exterior surfaces, protozoa are indirectly engaged in the generation of CH₄ (Morgavi et al., 2013; Newbold & Ramos-Morales, 2020). Starch, cellulose, hemicellulose, pectin, and soluble sugars are used by protozoa to create metabolic H₂ and VFA, which are needed by archaea to create CH₄ (Newbold & Ramos-Morales, 2020). Saponin-containing plants can inhibit CH₄ emissions by reducing the protozoal population and changing rumen fermentation conditions (Morgavi, Jouany & Martin, 2008). For example, in an in vitro rumen simulation, adding 11.54 mg fenugreek saponins to a buffer medium containing rumen microorganisms (40 ml), it was found that the antigen-parasite activity was the highest at this time, reaching 39%. Protozoa concentration decreased from 19.5 to 11.9 (×10⁴) per ml and the number of fungi and methanogens also declined (Goel, Makkar & Becker, 2008a). Adding 48, 54, 60, or 66 mg fenugreek plant material to 200 mg vetch-oat hay, as the basal feed in an in vitro rumen simulation, reduced protozoan numbers by 45, 35, 72 and 67%, respectively (Arhabbr, Ablabr & Zitouni, 2014). This was mainly attributed to the strong anti-protozoal activity of saponins. The lipid membranes of bacteria can form compounds with saponins, increasing their permeability and creating an imbalance that triggers microbial breakage (Kumar et al., 2016; Goel & Makkar, 2012; Ibidhi & Salem, 2022). Protozoa and methanogens exhibit endo- or exo-symbiosis in the rumen, so CH₄ production by the combination of protozoa and methanogens depends on the extent of symbiosis between methanogens and protozoa, as well as the methanogenesis rate of each methanogenic strain (Machmuller, Soliva & Kreuzer, 2003). Suppressing protozoa reduces their H₂ production; methanogenic bacteria need H₂ to reduce CO₂, so this reduces CH₄ production (Tapio et al., 2017). However, there are other reports that although saponins suppress the growth of protozoa and methanogens, they have no effects on CH₄ production. This could be due to the slow binding between protozoa and methanogens, or the increased metabolism of methanogens after the addition of saponins, resulting in increased CH₄ production (Patra, Kamra & Agarwal, 2006). The effect of saponins on protozoans may be temporary because bacteria can degrade saponins into sapogenins, which do not affect protozoans. Fenugreek saponins also inhibit fungal populations, which, like protozoa, interact closely with methanogens and are thought to promote CH₄ production (Goel, Makkar & Becker, 2008a). Li (2015) reported that by adding 50 mg fenugreek extract to 500 mg fermentation substrate, the number of fiber-degrading bacteria Butyrivibrio fibrisolvens and Fibrobacter succinogenes are significantly reduced, while methanogenic bacteria and protozoa are not significantly different from the control group. Butyrivibrio fibrisolvens and Fibrobacter succinogenes can not only degrade cellulose, but also perform biohydrogenation, which can reduce unsaturated fatty acids in the rumen to conjugated linoleic acid. CH₄ production may be influenced by the fatty acid biohydrogenation pathway, suggesting that this may be an alternative pathway for CH₄ reduction in fenugreek (Hassan et al., 2020).

Fenugreek is a superior forage plant that significantly reduces CH₄ emissions in simulated in vitro rumen fermentations, which may be related to the abundant tannin in fenugreek (Niu et al., 2021). Naseri, Hozhabri & Kafilzadeh (2013) reported that the tannin content of fenugreek seed was 3.8 g/kg, more than twice that of asparagus root (1.5 g/kg), and much higher than that of alfalfa hay (0.4 g/kg). In a study involving 17 plants containing polyphenols, a negative correlation was observed between total phenol, total tannic acid, or tannin activity, and CH₄ production, which indicates the potential CH₄-reducing ability of fenugreek (Jayanegara et al., 2009). Tannins can inhibit the interactions between methanogens and protozoans, by binding to adhesion proteins, or part of the cell wall, decreasing interspecies H₂ transfer and inhibiting the growth of methanogenic bacteria, thereby reducing the numbers of methanogens and protozoa, directly or indirectly (Doepel et al., 2012). Tannins can also inhibit the production of CH₄ by reducing the activity of fiber-degrading bacteria; the H₂ provided by fiber degradation is the substrate for the conversion of pyruvate to acetate in the CH₄ biosynthesis pathway (Tavendale et al., 2005). Min et al. (2005) showed that concentrated tannin reduced the number of fiber-degrading bacteria in the rumen, thereby reducing the microbial digestibility of dietary fiber polysaccharides and CH₄ production. However, the mechanism of action by which fenugreek tannins inhibit CH₄ production is not clear. It may influence microbial fermentation through antibacterial activity against specific rumen microbial strains, or selectively regulate specific rumen bacteria and fungi.

Fenugreek flavonoids are effective antibacterial agents, inhibiting gram-positive bacteria by interfering with the formation of cell walls, nucleic acids, or membranes (Olagaray & Bradford, 2019). Oskoueian, Abdullah & Oskoueian (2013) found that quercetin can reduce the proliferation of ciliate protozoa and methanogens in vitro. In addition, plant essential oils generally have antibacterial activity against a variety of rumen microorganisms, can effectively reduce the number of methanogenic bacteria in rumen fluid, and are most effective against gram-positive bacteria (Szumacher-Strabel & Cieslak, 2010). However, there has been no report to date on the effect of fenugreek essential oil on rumen microorganisms in vivo.

Effects of fenugreek on volatile fatty acid production.

The anaerobic environment of the rumen results in incomplete fatty acid metabolism and the final products are VFAs and CO₂, so analysis of VFAs can indirectly reflect the status of rumen fermentation (Ugbogu et al., 2019). Adding 10% fenugreek to the alfalfa hay substrate increased the metabolic rate of dry matter (DM) in a rumen simulation, decreasing the VFAs concentration and total gas production (CH₄, NH₃, CO₂). This was attributed to fenugreek contributing a higher proportion of substrate to microbial biomass production, indicating its effectiveness in influencing the supply of metabolized DM to rumen microbes (Naseri, Hozhabri & Kafilzadeh, 2013). Fenugreek- and alfalfa-based substrates did not result in differences in pH, or VFAs production, but fenugreek increased the proportion of propionic acid produced by an in vitro rumen simulation (Mir et al., 1997). Goel, Makkar & Becker (2008a) also observed a slight increase in the proportion of propionic acid in the VFAs produced at low fenugreek concentration (5.6 mg/40 ml). It’s indicated that fermentative FG reduces CH₄ uptake by H₂ or increases propionic acid uptake by H₂ by decreasing methanogenic activity by reducing CH₄ production (Mir et al., 1997; Tapio et al., 2017).

Propionic acid is the only gluconeogenic VFA that has the ability to enhance the efficiency of metabolizable energy utilization throughout the animal. In general, the ratio of acetic to propionic acid affects CH₄ production, and the lower the ratio, the lower the CH₄ production (Moorby & Fraser, 2021). This is because propionic acid provides an alternative pathway to metabolize H₂, away from CH₄ production (Ku-Vera et al., 2020). The effect of fenugreek on VFAs appears to be mediated by saponins, which can inhibit the growth of gram-positive bacteria and reduce their acetic acid production, while increasing the intestinal adhesion of gram-negative bacteria and their propionic acid production, thereby reducing CH₄ production (Jayanegara et al., 2020). Saponin-rich plants can selectively regulate the rumen microbial population to enhance propionic acid production, so a decrease in the ratio of acetic acid to propionic acid is generally accompanied by reduced CH₄ production (Ugbogu et al., 2019).

Effect of fenugreek on CH₄ emissions.

Many other studies have reported fenugreek’s positive effects on CH₄ emissions (Table 2), and no serious adverse effects of fenugreek ingestion in ruminants have been reported to date (Goel, Makkar & Becker, 2008b; Kala, 2019; Mohini, 2007). In an in vitro simulation experiment, CH₄ was reduced by 15.1% when 50 mg fenugreek was added to 60 ml fermentation broth, and no significant effects were found on fermentation pH and TVFA’s concentration (Li, 2015). Kumar et al. (2016) found that a 2% fenugreek seed supplement reduced CH₄ by 22.8% in an in vitro rumen simulation, improved DM and organic matter digestibility, and increased the feed degradation rate. The addition of 19, 21, 23, or 25% fenugreek to vetch-oat to in vitro rumen simulation, decreased CH₄ production by 45, 35, 72, or 67%, respectively, which may be beneficial for improving nutrient utilization and animal growth (Arhabbr, Ablabr & Zitouni, 2014). The positive effects of fenugreek on CH₄ emission are mainly attributed to its secondary metabolites. In addition, the content of several fatty acids, especially linoleic acid, is much higher in fenugreek than in other fodder crops, which can reduce the activity of rumen methanobacteria and change the process of biohydrogenation (Islam et al., 2017). However, Silva et al. (2021) reported that supplementation of 16 g of whole-seed fenugreek meal per day in the basal diet of dairy cows has no significant effect on rumen pH, NH₃-N, TVFA’s concentration, C₂:C₃ ratio and enteric CH₄ emissions. Rejil & Mohini (2006) also found that TVFA’s concentration, bacterial biomass, total gas as well as CH₄ production were not affected after adding fenugreek extracts to the diet. The reasons for this difference may be related to the experimental environment, animal species and the dosage of fenugreek.

Table 2:

Effects of fenugreek on CH₄ emissions from ruminants.

Source	Animal/ organism	Doses	Effects	References
Fenugreek seeds saponin	In vitro	11.54 mg/40 ml (buffered rumen fluid)	CH4 reduction of 1.97%; 39% reduction in protozoa; methanogens of bacteria and fungi were reduced	Goel, Makkar & Becker (2008a)
Fenugreek	In vitro	2.5%, 5%, and 7.5% of substrate	CH4 inhibition of 19.5%, 26.1%, 35.3%, respectively	Pattanaik et al. (2018)
Fenugreek	In vitro	(100% of fenugreek; 50:50 mixture of fenugreek and alfalfa; 100% of alfalfa) as substrate	CH4 (ml/g DM) (42.8, 52.6, 64.1); Methanogen (2, 1, 3.02, 4.23) (×104/mL); acetate: propionate (3.25,3.40,3.56); respectively	Niu et al. (2021)
Fenugreek leaf extract	In vitro	20 mg/30 ml (buffered rumen fluid)	CH4 inhibition of 16.6% (37.3–30.1) (ml/g DM); ratio of acetate to propionate is reduced (3.39–2.85)	Dey (2015)
Fenugreek	In vitro	19, 21, 23, or 25% of vetch-oat hay	CH4 inhibition of 45, 35, 72, or 67%, respectively	Arhabbr, Ablabr & Zitouni (2014)
Fenugreek seeds	In vitro	66 mg/40 ml (buffered rumen fluid)	CH4 reduction of 9.7%; 56% reduction of protozoa (357–157) (×103 per ml)	Goel, Makkar & Becker (2008b)
Fenugreek seeds	In vitro	2% of substrate	CH4 reduction of 22.8% (24.30–18.75) (ml/g DM)	Kumar et al. (2016)
Fenugreek seeds	In vitro	1% of substrate	CH4 reduction of 34.1%	Lakhani et al. (2019)
Fenugreek extract	In vitro	50 mg/60 ml (buffered rumen fluid)	CH4 reduction of 15.1%	Li (2015)
Fenugreek seeds	In vitro	2% of substrate (wheat straw and concentrates mixture in the ratio of 60:40)	CH4 reduction of 19.6 (34.22–27.5) (ml/g DM)	Mohini (2007)
Fenugreek seed extracts	In vitro	2% of substrate	CH4 production, TVFA concentration and bacterial biomass were not affected	Rejil & Mohini (2006)
Fenugreek straw	In vivo/cull sheep	40% of diet	CH4 reduction of 26.8%	Bhatt et al. (2021)
Whole-seed fenugreek powder	In vivo/dairy cows	16 g/cow/day	No significant difference between CH4 and acetate: propionate	Silva et al. (2021)

DOI: 10.7717/peerj.16842/table-2

Notes:

DM: dry matter.

Fenugreek in moderate doses does not have harmful effects on ruminants, but more long-term studies in vivo are needed to verify its effect and explore the specific mechanism of action.

Nutritive value of fenugreek

Fenugreek seeds contain 58% carbohydrate, 23–26% protein, 6.4% fat, 25% fiber, 6% volatile oil, 3% ash, 1.6% starch, and 0.4% soluble sugar. Fenugreek leaves contain 6% carbohydrate, 4.4% protein, and 1.1% fiber (Syed et al., 2020). Fenugreek seed protein is of good quality, with a higher content and a better amino acid composition than soy protein isolate. Additionally, compared to soy protein, it has higher denaturation temperature, foaming capacity, solubility, and stability, which makes it a useful source of protein for a range of functional meals (Wijekoon et al., 2021). Fenugreek seeds are also abundant in minerals including K, Mg, Ca, Zn, Mn, Cu and Fe; 53 elements have been isolated from fenugreek seeds, of which 11 are essential to the human diet, and their contents are in the order of Fe > Zn > Mn > Cu > Mo > Ni > V > Cr > Co > Si > Se (Srinivasan, 2006). Numerous vitamins, such as vitamins A, B₁, B₂, C, niacin, and nicotinic acid, are also abundant in fenugreek seeds. There are 17 main fatty acids in fenugreek, including linoleic, oleic, and linolenic acids, the majority of which are unsaturated (Table 4) (Ahmad et al., 2016).

Conclusions and recommendations

CH₄ released by ruminants is a major contributor to greenhouse gas emissions and energy loss, and in the upcoming years, ruminant production systems will confront even greater difficulties. As a result, methods to reduce CH₄ production while preserving animal health and productivity are being developed and researched. The profound influence of rumen fermentation on ruminant nutrition, food production and the environment has stimulated extensive research into managing the rumen microbiome to maximize productivity and reduce the environmental impact of ruminant production; dietary intervention to achieve these goals is a promising approach. When it comes to controlling the rumen flora and reducing the generation of CH₄, fenugreek and its secondary metabolites—such as saponins, tannins, and flavonoid compounds—have shown inconsistent outcomes during rumen fermentation. However, most studies have shown that the addition of fenugreek or its bioactive compounds to the basal feed reduces CH₄ production and improves rumen fermentation. In addition, fenugreek, as a dietary additive, can promote animal growth and increase the utilization potential of feed. Its rich nutrient content and the relative abundance of the growth promoter, diosgenin can improve the daily weight gain of beef cattle and sheep, and shorten the achievement of a commercially-acceptable weight. Dietary fenugreek improves milk yield and quality, mainly mediated by flavonoids and trigonelline, which affect the endocrine system and hormone secretion and ameliorate oxidative stress. Therefore, the livestock feed industry has the opportunity to develop natural, environmentally-friendly feed additives based on fenugreek.

This review has identified some gaps and weaknesses in past fenugreek research, which should be addressed by future research, i.e.: (1) Studies on the use of fenugreek to reduce CH₄ emissions from ruminants were mostly performed by short-term in vitro simulations; long-term in vivo trials will be needed to confirm the efficacy of fenugreek under real conditions; (2) the mechanisms of action by which fenugreek secondary metabolites influence the composition and metabolic activity of rumen bacteria are poorly understood and further research into effective strategies for CH₄ emission reduction is needed; (3) the efficacy of fenugreek in promoting lactation and improving growth performance, and its toxicological safety is influenced by factors such as dose, animal species and strain, and environmental conditions, so future research should aim to improve understanding of these factors. Future research should also aim to improve understanding of the potential benefits of fenugreek, explore the mechanisms of action of its various components and functions, and clarify the optimal level and formulation of fenugreek supplementation, to provide a theoretical basis for further development of its application in ruminants.