Cashew Nut Shell (Anacardium occidentale L.) Extract: A Natural Solution for Reducing Methane Emissions in Ruminants

Correspondence to: [email protected]

Summary

The intensification of the global climate crisis, coupled with rising demand for animal products, necessitates sustainable strategies to mitigate livestock greenhouse gas (GHG) emissions while enhancing productivity. Cashew Nutshell Extract (CNSE), a byproduct rich in phenolic compounds like anacardic acid, has emerged as a promising natural feed additive for reducing enteric methane emissions in ruminants. This review evaluates CNSE's potential to mitigate methane emissions, improve rumen fermentation, and enhance animal performance. In vitro studies demonstrated that CNSE reduced methane emissions by 8–18% at doses of 5–10 mg/60 mL rumen fluid, with higher doses showing greater efficacy. However, results varied with diet composition, dosage, and animal species, with some studies noting reduced fiber digestibility at higher CNSE concentrations. CNSE shows significant potential as a sustainable strategy for reducing enteric methane emissions and enhancing ruminant productivity. However, its efficacy requires optimized dosages and formulations tailored to specific diets and animal species. Long-term in vivo studies are needed to validate safety, scalability, and economic viability. With further research, CNSE could play a pivotal role in decarbonizing livestock systems while supporting global food security.

Introduction

The use of feed additives in livestock production has been a common practice to improve feed efficiency and overall animal performance (Gadzama et al., 2025). However, concerns over antibiotic resistance and drug residues have led to a search for natural alternatives (Compton et al., 2023). Cashew Nut Shell Extract (CNSE), also known as Cashew Nut Shell Liquid (CNSL), is a byproduct of the cashew industry with growing applications in sustainable agriculture. Derived from the honeycomb structure of cashew nutshells (Figure 1), CNSE contains phenolic compounds like anacardic acid, cardanol, and cardol, which exhibit antimicrobial properties (Danielsson et al., 2014). These compounds are increasingly recognized for their potential to reduce methane emissions in ruminants—a critical goal given that livestock accounts for approximately 14.5% of global anthropogenic greenhouse gas emissions, with enteric methane being a major contributor (FAO, 2023; Moraes et al., 2014; Gadzama, 2025).

Figure 1. Cashew nutshell liquid derived from the honeycomb structure of cashew nutshells

Cashew Nut Shell Extract: A Promising Feed Additive

CNSE is a viscous, reddish-brown liquid rich in bioactive phenolics. Historically underutilized, cashew nutshells contain 25–34% oil, which has gained industrial interest in recent decades (Pandiyan et al., 2000). The primary components of CNSE include—anacardic acid (79%), cardanol (14%), and cardol which act as surfactants, disrupting bacterial membranes and inhibiting methanogens (Figure 2). These compounds can influence rumen microbial populations, potentially reducing methane emissions and altering volatile fatty acid (VFA) production. Watanabe et al. (2010) reported that CNSL inhibited methane formation and increased propionate production in vitro, suggesting its potential as a feed additive for ruminants. Recent advancements in green extraction methods, such as solvent-free mechanical pressing, have improved the cost-effectiveness and sustainability of CNSE production (Cardolite, 2017; Alaka et al., 2024).

Figure 2. Composition of Cashew Nut Shell Liquid (CNSL).

Adapted from Alaka et al. (2024)

The Potential of CNSE in Methane Mitigation

Methane mitigation is a priority in livestock management (Gadzama et al., 2025). CNSE’s anti-methanogenic properties offer a natural solution for methane mitigation in ruminants (Compton et al., 2023). In vitro studies demonstrate that CNSE reduces methane production by 8–18% depending on dosage, primarily by inhibiting methanogenesis-related genes like mcrA (Shinkai et al., 2012; Danielsson et al., 2014). Comparatively, synthetic additives like 3-nitrooxypropanol (3-NOP) achieve higher methane reductions (30%) (Gadzama, 2024), but CNSE’s natural origin and dual benefits for rumen fermentation make it a safer, more sustainable alternative (Compton et al., 2023; Sarmikasoglou et al., 2024).

Figure 3. Effects of CNSE on In Vitro Rumen Fermentation

Effects of CNSE on In Vitro Methane Reduction

In vitro trials highlight CNSE's dose-dependent efficacy. Danielsson et al. (2014) reported an 18% methane reduction at 10 mg CNSE/60 mL rumen fluid, attributed to suppressed methanogen activity and increased propionate-producing bacteria like Prevotella ruminicola. However, results vary in vivo. Branco et al. (2015) observed only an 8% methane reduction trend in lactating cows fed technical-grade CNSL, likely due to processing-induced loss of anacardic acid. This inconsistency underscores the need for standardized CNSE formulations and further in vivo studies (Sarmikasoglou et al., 2024).

Effect on Ruminal pH and VFA Production

Compton et al. (2023) found that CNSE supplementation had no significant effect on culture pH, which averaged 5.76 across all treatments. Similarly, total volatile fatty acid (VFA) concentration and the molar proportions of individual VFAs (acetate, propionate, butyrate, isovalerate, and valerate) were unaffected by CNSE. These results contrast with previous studies that reported a shift in VFA production towards propionate with CNSL supplementation (Watanabe et al., 2010; Shinkai et al., 2012). The authors suggested that the lack of effect on VFA production in their study could be due to the specific composition of CNSE used, which contained 59% anacardic acid and 18% cardol.

Effect on Nutrient Digestibility

Compton et al. (2023) reported that CNSE supplementation did not affect the apparent digestibility of DM, OM, NDF, or starch in vitro. These findings align with those of Sarmikasoglou et al. (2023), who observed no changes in nutrient digestibility under continuous culture conditions. However, Shinkai et al. (2012) reported a decrease in DM and OM digestibility in vivo when higher doses of CNSL were fed, suggesting that the effects of CNSE may be dose-dependent.

Antimicrobial and Antimethanogenic Effects

CNSE's phenolic compounds, particularly anacardic acid, disrupt gram-positive bacteria and methanogenic archaea. By reducing hydrogen and formate availability—key substrates for methane production, CNSE shifts rumen fermentation toward propionate, a volatile fatty acid that enhances energy efficiency in ruminants (Shinkai et al., 2012). This mechanism mirrors the effects of tannins, another class of plant-derived compounds, but CNSE's higher solubility improves its bioavailability in the rumen (Patra & Saxena, 2010).

Implications of the Findings

Integrating CNSE into livestock diets could address environmental and productivity challenges. Although CNSE did not significantly alter VFA production or nutrient digestibility (Compton et al., 2023), previous research has shown that CNSL can reduce methane emissions by inhibiting hydrogen and formate production, which are essential for methanogenesis (Watanabe et al., 2010). This suggests that CNSE could still have potential as a methane mitigation strategy, particularly at higher doses or in combination with other dietary interventions. By reducing methane emissions, CNSE aligns with global climate goals, such as the Paris Agreement’s target to limit warming to 1.5°C (IPCC, 2023). Additionally, its ability to enhance propionate production may improve feed efficiency, translating to higher milk yields and weight gain in cattle (Goetz et al., 2023). However, challenges persist:

Palatability and Dosage: High phenolic content may deter feed intake, necessitating encapsulation or flavor-masking technologies (Aderinboye et al., 2018).

Economic Viability: Scaling CNSE production requires investment in cashew byproduct processing infrastructure, particularly in developing nations like India and Vietnam, which dominate cashew cultivation (Alaka et al., 2024).

Conclusion

CNSE represents a dual-purpose solution for sustainable livestock farming, offering methane mitigation and improved rumen efficiency. While in vitro results are promising, translational in vivo studies are critical to optimize dosing and mitigate variability. Future research should prioritize long-term safety assessments and explore synergies with other additives, such as seaweed-derived bromoform, and different dietary compositions to fully understand its potential as a feed additive for ruminants. 

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