Effect of licorice on production performance, gastrointestinal health and immunity of broiler chickens: A review

Introduction

Licorice (Glycyrrhiza glabra) is one of the oldest medicinal herbs and has gained increasing attention as a phytogenic feed additive in poultry production due to its diverse biological activities. It belongs to the family Fabaceae and is native to Central and South-Western Asia and the Mediterranean region. The dried root contains numerous bioactive compounds including triterpene saponins, flavonoids, glycyrrhizin, glycyrrhetinic acid, phytosterols, coumarins, amino acids, tannins, volatile oils and phenolic compounds. Glycyrrhizin, the principal active constituent, accounts for approximately 10% of the dry root weight and possesses a sweetness nearly 50 times greater than sucrose. Other important constituents such as liquiritin, isoliquiritin, glabridin and various flavonoids contribute to the antioxidant, antimicrobial, anti-inflammatory and immunomodulatory properties of licorice (Shibata, 2000;Simmler et al., 2013;Pastorino et al., 2018;Rizzato et al., 2017) [39, 41, 31, 35] .

Antioxidant properties

The high phenolic and flavonoid content of licorice confers strong antioxidant activity through free radical scavenging, metal ion chelation, inhibition of lipid peroxidation and enhancement of endogenous antioxidant defense systems (Visavadiya et al., 2009). Glabridin has been identified as one of the most potent antioxidants, effectively inhibiting low-density lipoprotein oxidation and reducing cholesteryl linoleate hydroperoxide formation (Vaya et al., 1997;Carmeli and Fogelman, 2009). Moreover, glycyrrhizic acid suppresses cyclooxygenase activity and prostaglandin E₂ synthesis, thereby reducing inflammatory responses. Glycyrrhetinic acid also exhibits glucocorticoid-like activity, enhancing stress tolerance and modulating inflammatory pathways (Shibata, 2000;Damle, 2014) [46, 43, 7, 39, 5] .

Immunomodulatory properties

Licorice

has also demonstrated considerable immunomodulatory potential. Glycyrrhetinic acid stimulates the production of cytokines, antibodies, T-lymphocytes and interferon-γ, thereby strengthening both innate and adaptive immunity (Kataria et al., 2013;Dhama et al., 2015;Dhama et al., 2018). It has also been shown to activate toll-like receptor 4 signaling, which plays an essential role in pathogen recognition and immune activation (Peng et al., 2011). In poultry, supplementation with licorice has been associated with increased spleen and bursa weights, suggesting enhanced immune competence and disease resistance (Kalantar et al., 2017) [24, 9, 10, 32, 23] .

Hypo-cholesterolemic properties

Another important biological property of licorice is its hypocholesterolemic effect. Phytosterols present in licorice interfere with intestinal cholesterol absorption by competing with cholesterol for micelle incorporation, while dietary fiber and saponins enhance bile acid excretion and hepatic cholesterol clearance (Ostlund, 2004;Venkatesan et al., 2003). Consequently, supplementation with licorice has been reported to reduce serum total cholesterol and LDL cholesterol concentrations (Visavadiya and Narasimhacharya, 2006; Alagawany et al., 2019) [29, 44, 45, 2] .

Antimicrobial properties

The antimicrobial activity of licorice has been attributed primarily to its flavonoids, saponins and alkaloids. These phytochemicals inhibit the growth of several pathogenic bacteria, including Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Bacillus subtilis, by suppressing bacterial gene expression and toxin production (Gupta et al., 2008;Nitalikar et al., 2010;Sharma et al., 2013;Wang et al., 2015). Such antimicrobial effects may contribute to improved gastrointestinal health and nutrient utilization in poultry [16, 28, 38, 47] .

Beneficial Effects Effect on Growth Performance

The influence of licorice supplementation on growth performance has been inconsistent across studies. Several investigations reported no significant effects on body weight gain in broiler chickens receiving dietary or water supplementation of licorice extract (Sedghi et [37, 25, 26, 21, 18, 17, 34, 33, 22, 14, 37, 20, 25, 26, 36, 21, 14, 11, 17, 27, 17, 34, 22, 26, 11, 48] .

Effect on Carcass Characteristics

Most studies suggest that licorice supplementation has little influence on carcass yield or organ weights. Naser [17, 34, 33, 37, 27] .

Effect on Immune Response

The immunostimulatory properties of licorice have been widely recognized. Supplementation has been associated with increased spleen weight (Nasra et al., 2010) and enhanced humoral immunity, as evidenced by higher haemagglutination inhibition antibody titers against Newcastle disease virus in broilers receiving standardized licorice extract (Jagadeeswaran and Selvasubramanian, 2014). However, some studies observed no significant effects on antibody titers or lymphoid organ weights (Moradi et al., 2014;Beski et al., 2019) indicating that immune responses may vary according to dosage, extract type and management conditions [27, 19, 25, 6] .

Effect on Serum Cholesterol

Numerous studies support the cholesterol-lowering effect of licorice supplementation. Al-Daraji (2012a) demonstrated reduced plasma cholesterol concentrations in broilers fed aflatoxin-contaminated diets supplemented with licorice extract. Likewise, Naser et al. (2017) reported decreased serum total cholesterol and LDL cholesterol concentrations in broilers receiving licorice extract through drinking water. Similar reductions were observed in Japanese quails (Dosoky et al., 2021), although some studies reported non-significant changes despite numerically lower cholesterol levels (Aghdam Shahryar et al., 2018; Hosny et al., 2020) [4, 26, 12, 1, 17] .

Effect on Antioxidant Status

Licorice supplementation consistently enhances antioxidant defense mechanisms in poultry. Dietary inclusion significantly increases total antioxidant capacity while reducing total oxidant status and oxidative stress indices (Dogan et al., 2018;Sibel et al., 2018). Furthermore, licorice extract lowers serum malondialdehyde concentrations, indicating reduced lipid peroxidation (Dosoky et al., 2021). These antioxidant properties are primarily attributed to flavonoids and phenolic compounds that neutralize reactive oxygen species and improve cellular antioxidant systems [11, 40, 12] .

Effect on Heterophil-to-Lymphocyte Ratio

The heterophil-to-lymphocyte (H/L) ratio is widely recognized as an indicator of physiological stress in poultry. Several studies demonstrated that licorice supplementation significantly reduces the H/L ratio, particularly under stress conditions such as aflatoxin exposure, indicating improved stress tolerance and immune competence (Al-Daraji, 2012a; Al-Daraji, 2012b). However, other researchers found no significant changes in leukocyte profiles following licorice supplementation (Sedghi et al., 2010;Moradi et al., 2014;Aghdam Shahryar et al., 2018;Dosoky et al., 2021;Geravand et al., 2021). Similar reductions in H/L ratio have also been reported with other phytogenic feed additives including asparagus root powder, lemongrass, thyme, garlic combinations and herbal essential oils, suggesting that phytogenic additives may effectively alleviate physiological stress in poultry [4, 5, 37, 25, 1, 12, 14] . Ullah et al. (2024) reported that dietary liquorice supplementation @ 2ml/L significantly enhanced intestinal morphology (P<0.05) in broilers, by increasing villus height, villus width, and villus height-to-crypt depth ratio, together with reduced crypt depth, suggesting improved gut health and nutrient absorption. Similar results were reported by Gowthaman et al. (2024), stating that supplementation of liquorice root powder at 0.3% level in the broiler diet significantly increased (P<0.05) the jejunal villus height, villus width and villus height to crypt depth ratio. Also, Pappula et al. (2026) reported that supplementation of licorice in the broiler diet improved the gut morphology (villus height, villus width, crypt depth and villus height to crypt depth ratio). Intestinal histomorphometry of broilers had appositive effect by the supplementation of 0.1% licorice root powder when given in combination with asparagus root powder and lemongrass oil (Dr et al., 2023) [42, 15, 30] .

Effect on Intestinal Histomorphometry

Conclusion

Overall, the available literature indicates that licorice root powder and its extracts possess substantial antioxidant, antiinflammatory, antimicrobial, immunomodulatory and hypocholesterolemic properties that make them promising phytogenic feed additives in poultry nutrition. Although responses in growth performance are variable among studies, most evidence suggests that appropriate inclusion levels improve feed efficiency, antioxidant status, immune response, serum lipid profile and stress resistance without adversely affecting carcass characteristics. Variations among experimental findings are likely related to differences in dosage, extraction method, bird species, environmental conditions and duration of supplementation. Future studies focusing on standardized preparations, optimal inclusion levels and underlying molecular mechanisms, particularly in straight-run broiler chickens, are required to fully establish the practical benefits of licorice root powder in commercial poultry production.

• Conflict of Interest: Not available • Financial Support: Not available

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