Phytogenic as a natural resource for gut health management: a sustainable strategy for modern poultry production

Abstract

The increasing global demand for poultry products has intensified the need for intervention strategies that enhance productivity while maintaining animal health and food safety. Antimicrobials have historically been used in poultry production to support growth performance and maintain gut health; however, their routine and prolonged use have raised significant concerns regarding antimicrobial resistance, which poses a serious threat to public health. The growing concerns regarding antimicrobial resistance have motivated researchers to seek safer, more sustainable alternatives. This review critically evaluates the mechanisms by which phytogenic feed additives (PFAs) regulate gut health and their potential to support sustainable poultry production as alternatives to conventional antimicrobials. Phytogenic compounds have been shown to enhance intestinal barrier integrity by upregulating tight junction proteins, improve nutrient absorption by stimulating digestive enzyme activity, and promote villus development and mucosal health. Furthermore, these bioactive molecules have demonstrated potential to modulate microbial ecology by favoring beneficial taxa while suppressing pathogenic colonization, thereby improving gut homeostasis and immune competence. These combined effects contribute to improved overall production sustainability. Despite the beneficial effects of PFAs, variation in plant sources, bioactive component concentrations, extraction methods, and dosage leads to inconsistent poultry responses, a limitation that warrants further investigation and standardization. However, advances in formulation technologies and standardization strategies are progressively improving their consistency and practical application. Therefore, PFAs represent a viable nutritional strategy to support gut health and promote more sustainable poultry production with reduced reliance on conventional antimicrobials.

1. Introduction

The global demand for poultry meat and eggs continues to increase, driven by population growth and the rising need for affordable animal protein. This trend has intensified pressure on poultry production systems to maximise efficiency and productivity (Aminullah et al., 2025a). Modern broiler strains are characterised by rapid growth and high metabolic rate, requiring a continuous and adequate supply of nutrients through feed. These nutrients are not only essential for growth and tissue development but also play a critical role in supporting metabolic processes and maintaining systemic morphological and physiological balance. To handle the environmental and management stressors often found in intensive production systems, the birds must utilise these nutrients more efficiently than low-potential genetic strains do. Therefore, maintaining optimal nutrient utilisation and physiological resilience has become a key priority in modern poultry production (Basiouni et al., 2023).

The gastrointestinal tract (GIT) is the primary site of biological nutrient digestion, delivery, and utilisation, recognised as a prerequisite for poultry production and productivity (Celi et al., 2017). The GIT is also exposed to substantial physiological stress (Wickramasuriya et al., 2022), which affects its morphology, function, and health (Urban et al., 2025).

Chemical-based antimicrobials are widely and globally used for the treatment and prevention of bacterial infections and have historically been used as growth promoters in poultry production. Their use helps maintain gut health by reducing gut microbial load and competing for nutrient utilisation (Khan & Iqbal, 2016), thereby supporting the birds' growth. In addition, antimicrobials help to prevent pathological changes and maintain the intestinal tract's functional potential (Adedokun & Olojede, 2019). Therefore, their use often promotes gut health by boosting nutrient digestion, absorption, and metabolism. These advantages help reduce physiological stress and improve growth performance. As a result, antimicrobials have traditionally been used to increase productivity in the poultry production sector (Liu et al., 2024). Nonetheless, there is growing concern that the extensive use of antimicrobials contributes to the rise of antimicrobial resistance (AMR), posing risks to both animal and human health (Aminullah et al., 2025b; Azizi et al., 2024a).

Owing to global public health concerns, some countries, such as those in the European Union [Regulation (EC) No 1831/2003], have completely banned antibiotics as growth promoters in livestock and poultry production, while others, including China, India, and various developing nations, have imposed restrictions (Adetunji et al., 2025; Attia et al., 2020). Considering these limitations, many researchers suggest a future strategy to reduce reliance on antimicrobial use in livestock production (EFSA Panel on Biological Hazards [BIOHAZ], 2021; Boix-fayos & Vente, 2023; Liu et al., 2023). The alternative strategy should address both optimising gut health and preventing antimicrobial resistance without compromising poultry productivity.

As potential substitutes, phytogenic compounds containing bioactive compounds are suggested to provide natural antimicrobial effects that inhibit pathogen growth (Urban et al., 2025; Aminullah et al., 2025b), thereby contributing to sustainable poultry production. Phytogenic-derived active molecules, such as rosmarinic acid and flavonoids, are well known for exerting biological effects, including reducing oxidative stress, enhancing antioxidant capacity, and improving immune competence in poultry (Peter et al., 2021). These properties make them promising and green alternatives to conventional antibiotics as growth promoters in poultry production, as demonstrated by various studies (Liu et al., 2024; Aminullah et al., 2025b; Rachwał & Gustaw, 2025). Phytogenic substances, as natural alternatives, contribute to antibiotic-free or green food production, which supports human health and safety. To ensure a consistent, high-quality supply of bioactive compounds for poultry gut health management, advanced agricultural strategies such as micropropagation can be used to sustainably mass-produce disease-free, antioxidant-rich phytogenic resources, including 'Bentong' ginger (Zahid et al., 2025).

This review consolidates recent knowledge on the functional properties of phytogenic compounds and their potential as an alternative strategy for maintaining gut health in sustainable poultry production. Particular emphasis is placed on the mechanisms of phytogenic antimicrobial, antioxidant, and anti-inflammatory actions in the poultry biological system. Ultimately, the review highlights the relevance of phytogenic implications as an alternative nutritional strategy to support sustainable poultry production.

2. Methodology

This narrative review synthesised current knowledge on the role of phytogenic feed additives in poultry gut health and sustainable production. A comprehensive literature search was performed using major scientific databases, including Google Scholar, Scopus, PubMed, and Web of Science. Relevant publications from 2010 to 2026 were included to ensure coverage of both foundational and recent developments in the field. The search strategy employed combinations of keywords and search terms related to the review objectives, including “phytogenic feed additives”, “phytobiotics”, “gut health”, “intestinal microbiota”, “intestinal morphology”, “gut barrier integrity”, “antimicrobial activity”, “antioxidant activity”, “anti-inflammatory activity”, “broiler chickens”, “poultry nutrition”, and “sustainable poultry production”. Reference lists of relevant articles were also screened to identify additional studies for the review.

Studies were included if they: (i) investigated phytogenic feed additives or plant-derived bioactive compounds in poultry species; (ii) evaluated outcomes related to gut health, intestinal morphology, gut microbiota, digestive physiology, immune response, antioxidant status, antimicrobial activity, or production performance; and (iii) were published in peer-reviewed scientific journals in English. Review articles were included to provide conceptual and mechanistic perspectives, whereas experimental studies were used to support evidence-based discussion. Conference abstracts, duplicate records, non-peer-reviewed publications, and studies not directly related to poultry gut health were excluded. The selection process involved screening titles, abstracts, and full texts for relevance to this review's objectives. Particular attention was given to studies that provide mechanistic insights into the antioxidant, antimicrobial, and anti-inflammatory properties of phytogenic compounds, as well as their influence on the intestinal microbiota, gut morphogenesis, and physiological functions.

To improve the reliability of the evidence synthesis and minimise selection bias, the included studies were critically evaluated on the basis of methodological quality, clarity of objectives, experimental design, sample size, analytical procedures, statistical approaches, and relevance to the review topic. Greater emphasis was placed on studies published in reputable peer-reviewed journals that provided robust experimental evidence and clear methodological descriptions.

The selected literature was subsequently organised into thematic categories, including phytogenic feed additives and their bioactive compounds; antioxidant, antimicrobial, and anti-inflammatory mechanisms; intestinal microbiota; gut morphogenesis; physiological functions; and the implications of phytogenics for sustainable poultry production.

3. Phytogenics and their bioactive components

Phytogenic or phytobiotic compounds are plant-derived, biologically active substances that exert a wide range of effects on biological systems in the body. (Basiouni et al., 2023). The phytogenic compounds containing bioactive compounds may include, but are not limited to, terpenoids, alkaloids, flavonoids, phenolics, organosulfur compounds, saponins, and polysaccharides (Mountzouris & Brouklogiannis, 2024; Rachwał & Gustaw, 2025). Researchers have focused on bioactive compounds as potential natural alternatives to antibiotics in poultry production due to their growth-promoting properties (Mandey & Sompie, 2021). The selected phytogenic compounds and their biologically active components are listed in Table 1. Phytogenic compounds contain various bioactive molecules that can exert diverse metabolic and functional effects in biological systems, including inhibiting enzymes implicated in cellular damage, enhancing mitochondrial function, and improving metabolic efficiency and energy utilisation (Attia et al., 2025; Adetunji et al., 2025). Polyphenols are bioactive and functional components of phytogenics, and their concentrations vary across geographical regions, plant harvest stages, environmental factors, and processing techniques (Nurzyńska-Wierdak, 2023). The benefits of polyphenols are attributed to their ability to influence intestinal morphogenesis and systemic function, including the immune response, which may improve gut health and productive performance in poultry (Mnisi et al., 2023). However, inconsistencies in bioactive component concentrations, extraction methods, and delivery systems remain a challenge affecting the effectiveness of phytogenics in poultry production.

Table 1.

Phytogens and their bioactive components being used as PFAs in poultry production.

Phytogenic	Latin name	Plant family	Bioactive compound	Reference
Oregano	Oreganum vulgare	Labiateae	Carvacrol, thymol	Galamatis et al., 2025)
Thyme	Thymus vulgare	Labiateae	Carvacrol, thymol	Ceylan et al., 2025)
Garlic	Allium sativum L.	Alliaceae, Liliaceae	Diallyldisulfide, alliin, allicin
Chilli, Cayenne pepper	Capsicum frutescens	Solanaceae	Capsaicin
Peppermint	Mentha piperita	Labiateae	Menthol, carvacrol	Park & Kim, 2025
Cinnamon	Cinnamomumcassia	Lauraceae	Cinnamaldehyde
Anise	Pimpinella anisum	Apiaceae, Umbelliferae	Anethol

The potential antioxidant, antimicrobial, and anti-inflammatory effects of phytogenic in poultry have been demonstrated in various studies (Aminullah et al., 2025b; Rehman et al., 2025) and are explicated in the upcoming subheadings.

4. Phytogenics extraction method and delivery systems

One of the major factors influencing the effectiveness of PFAs is the extraction methods and delivery systems used. These factors critically influence the chemical composition, stability, and bioavailability of active compounds. The literature consistently highlights that the absence of standardised extraction protocols and insufficient reporting of processing details are key barriers to reproducibility. It emphasises the need for mandatory disclosure of extraction techniques, carrier systems, and encapsulation matrices to facilitate meaningful comparisons across studies (Gavris et al., 2019; Ipçak, 2023).

Traditional extraction techniques, such as steam distillation, solvent extraction, cold extraction, and maceration, produce highly variable concentrations of key phytochemicals. This variability depends on several factors, including the specific plant part used, the harvest season, the solvent polarity, and the processing conditions (Gavris et al., 2019). Solvent-based methods are cost-effective but can leave residual solvents and vary in their ability to retain bioactive compounds. In contrast, steam distillation yields high-purity essential oils but might degrade heat-sensitive compounds (Gavris et al., 2019). The literature indicates that Ultrasound-Assisted Extraction (UAE) is the most effective and consistent method, ensuring balanced yields, the safety of bioactive molecules, and a sustainable scalability strategy that uses non-thermal cell-permeabilising pretreatments (Kahraman, 2026).

However, the delivery system has a greater impact on outcome consistency than the extraction method alone. Comparative studies show that encapsulation methods, especially biopolymer-based nanoencapsulation with materials such as chitosan, consistently outperform non-encapsulated forms, such as powders or free oils, in eliciting predictable biological responses (Amiri et al., 2021). Encapsulation shields volatile compounds from oxidation and heat damage during feed processing, boosts their solubility in the gut's aqueous environment, enables controlled release, and enhances mucoadhesion. This reduces variability between individuals and consistency among study outcomes. Notably, the delivery system seems more crucial than the specific phytogenic compound: encapsulated formulations show significant effects at lower doses and more consistent results across experiments, whereas free or powdered forms yield highly variable outcomes even at higher inclusion levels (Hafeez et al., 2016; Amiri et al., 2021).

5. Functional properties of phytogenics

Phytogenics are plant-based derivatives that exert numerous beneficial effects on biological systems, which is why they are extensively studied to optimise and standardise their dosage, use, and delivery methods. The functional properties of phytogenics are explained in detail below.

5.1. Antioxidant properties

Polyphenols, the principal bioactive components in phytogenic substances, possess strong antioxidant properties that can enhance immune competence by maintaining the balance between free radical production and neutralisation in an in vitro model. Antioxidant activity is particularly improved along the intestinal lining, resulting in enhanced gut barrier integrity, function, and productive performance in poultry (Mehdi et al., 2018; Tian et al., 2020). The improved antioxidant capacity is attributed to increased antioxidant enzyme activities and decreased blood serum malondialdehyde levels (Y. Li et al., 2023). This strategy can be explained through the mechanistic approach to antioxidant enzyme activities, which alter signal transduction pathways, thereby reducing oxidative stress, improving cellular protection, and overall growth performance in poultry (Suria et al., 2019).

As antioxidant enhancers, phytogenic bioactive compounds interact with multiple biochemical molecules, mitigating the generation of reactive oxygen species (ROS), reinforcing detoxification, and protecting cellular components, such as lipids, proteins, and DNA, from oxidative damage (Piao, 2023). The mechanisms of action of different phytogenic compounds in interacting with reactive species differ. For example, the polyphenols can scavenge various ROS, such as hydroxyl radicals (HOs), peroxy radicals (ROOs), superoxide anions (O2−) (Hahn & Shin, 2020), and reactive nitrogen species (RNS) such as peroxynitrite (ONOO−) (Azizi et al., 2023). Thereby, polyphenolic compounds act as antioxidants either by donating a hydrogen atom from their hydroxyl (HO) group or by transferring a single electron to free radicals generated during lipid oxidation (Ekunseitan et al., 2023). Individually, bioactive compounds, such as curcuminoids and carotenoids, donate a single electron to double-bonded molecules, resulting in saturating unpaired peroxyl and oxygen free radicals (Polyakov et al., 2023), while organosulfur compounds, such as garlic, support redox buffering, which indirectly mitigates free radicals (Olson et al., 2023). In addition, lipophilic phytogenic compounds such as carvacrol and thymol act synergistically with flavonoids and carotenoids, thereby increasing access to polyunsaturated fatty acids, enhancing membrane integrity, and reducing microdomain sensitivity by intercepting lipid peroxyl radicals (Basiouni et al., 2023). The organosulfur constituents of garlic also boost the synthesis of glutathione (GSH) through regulating glutathione reductase activities (Sharma & Rani, 2023). Phytochemicals such as curcumin, isothiocyanate-like moieties, and terpenoids have also been reported to enhance antioxidant capacity by activating nuclear factor erythroid 2-related factor 2 (Nrf2) signalling (Qin et al., 2023). The molecules regulate the expression of heme oxygenase 1 (HO-1), glutathione peroxidases (GPx), superoxide dismutase (SOD), catalase (CAT), and glutamate-cysteine ligase (GCLC), boosting the antioxidant capacity along the intestinal lining and epithelial membranes (Hahn & Shin, 2020).

Phytogenics also reduce cytokine signalling and downstream NF-κB activity, thereby attenuating inflammatory responses by heterophils and macrophages (Laurindo et al., 2023). Furthermore, some bioactive compounds, such as plant-derived terpenoids, enhance electron-transfer efficiency, thereby reducing electron leakage and superoxide production (Piao, 2023). The mechanism involves regulating polar protein molecules, reducing H₂O₂ production, and stabilising mitochondrial membranes (Said & Ibrahim, 2024). Polyphenolic bioactive compounds can also alter fatty acid composition, shifting it from saturated to monounsaturated or polyunsaturated forms (Mnisi et al., 2023). In support of the above, dietary polyphenol-sourced antioxidants can spare the use of natural resources, such as alpha-tocopherol for lipid protection as well as vitamin C and carotenoids for ROS suppression (Said & Ibrahim, 2024; Shahidi & Camargo, 2016).

5.2. Antimicrobial properties

The development of multidrug-resistant microbes is an emerging concern that threatens animal and human health worldwide (Azizi et al., 2024a). To address this issue, researchers are motivated to develop safe and effective strategies to reduce antimicrobial resistance without compromising productivity in rapidly growing poultry (Zahir et al., 2026). Phytogenics as feed additives are reported as a promising natural resource for a sustainable strategy to reduce reliance on antimicrobial use in livestock production. The antibacterial and antiviral effects of phytogenic substances have been extensively studied and demonstrated in livestock and poultry (Mohamed & Hassan, 2023), yet the underlying mechanisms of action remain partially elucidated. However, the active compounds, such as flavonoids and isoprenoid glucosinolate derivatives, as well as thymol, cinnamaldehyde, and thyme oil, are of interest to researchers as potential green alternatives to antibiotic growth promoters for improved poultry welfare and production (Axmann et al., 2021). Various phytogenics, including thyme, garlic, and marjoram, have shown antibacterial effects against Escherichia coli and Salmonella typhimurium in the poultry intestinal tract (Urban et al., 2025).

Mechanistically, the literature reports various types of phytogenics and distinct antimicrobial modes of action. For instance, essential oils enter bacterial cells, block protein synthesis, and cause the expulsion of cytoplasmic components, leading to bacterial death (Singh et al., 2020). Essential oils initially prevent biofilm formation and disrupt adhesion to extracellular polymeric substances, thereby making pathogens more susceptible to host defence mechanisms and facilitating the penetration of antimicrobial agents (Touati et al., 2025). Likewise, lipophilic phytogenics, such as cinnamaldehyde, carvacrol, thymol, and eugenol, intercalate into the phospholipid layer of bacterial cell membranes (Nourbakhsh et al., 2022), disrupting membrane permeability and causing ion leakage, ultimately leading to cell lysis (Wijesundara et al., 2022). Bacterial cell permeability is also disrupted by the synergistic effect of an organic acid-essential oil combination in the intestinal lumen of poultry birds (Dong et al., 2024a).

Furthermore, some active ingredients of phytogenic compounds also bind to bacterial enzymes and cell membrane proteins, leading to inhibition of energy metabolism, disruption of bacterial sensing, and decreased expression of virulence factors (Murugan et al., 2025). Chimonanthus salicifolius-sourced flavonoids release the bacterial extracellular phosphatase, resulting in loss of intracellular components losses leading to DNA damage. Evidence suggests that Chimonanthus salicifolius can damage the cell wall and membrane, causing loss of intracellular substances, leading to DNA lysis and cell death (Zhou et al., 2023). Phytogenics such as spices and herbs interact with bacterial cell walls, disrupting their membranes and causing ion leakage, thereby decreasing microbial pathogenicity (Liu et al., 2017), or modifying permeability to H⁺ and K⁺ cations, leading to an imbalance (Ferdous et al., 2019).

The antimicrobial action mechanism of phytobiotics active ingredients also involves damage to bacterial cell glycolipid membranes, leading to compromised cell walls and reduced cytoplasmic content (Kiczorowska et al., 2017). Additionally, certain phytogenic compounds can produce ROS at higher concentrations in the bacterial cell, leading to changes in cell structure and function (Fathima & Rao, 2016). The changes lead to inhibition of protein and DNA synthesis and interfere with bacterial cell metabolism (Adetunji et al., 2025). Furthermore, some phytobiotic compounds suppress toxin gene expression, thereby reducing endotoxin production associated with inflammation (Basiouni et al., 2023), while others enhance intestinal tight junction structure and increase mucin production, thereby strengthening mucosal defence and reducing the inflammatory response (Farràs et al., 2020).

5.3. Anti-inflammatory properties

High-performing animals and poultry are frequently exposed to a range of stressors, encompassing environmental, nutritional, microbiological, and management-related factors. These stressors can induce oxidative stress, often referred to as "secret killers" for their role in impairing animal and poultry health and thereby compromising productive performance (Boix-Fayos & Vente, 2023). Inflammation is one of the internal stressors that contribute to ROS generation, leading to activation of oxidative processes at the cell membrane and peroxidation of mitochondrial and other organelle lipids, resulting in cell disruption and death (Bickler et al., 2020). This event results in tissue and organ damage. Various studies have concluded that 90% of pathological alterations in poultry are associated with chronic inflammation, largely driven by an imbalance in the gut microbiota (Shehata et al., 2022a; Basiouni et al., 2023).

On the other hand, regulatory effects of phytogenic substances on the gut microbiota, gut barrier integrity, and nutrient utilisation have been reported (Shehata et al., 2022a; Oni & Oke, 2025). Several studies have shown that natural compounds such as berberine, boswellia, marigold triterpenoids, eugenol, quercetin, resveratrol, and curcumin exhibit anti-inflammatory effects in poultry and livestock (Shehata et al., 2022b; Riaz et al., 2024; Oni et al., 2024). The anti-inflammatory effects of phytogenic active ingredients offer promising insights for researchers seeking an alternative strategy for sustainable poultry production.

Mechanistically, the available literature indicates that each type or group of phytobiotics exhibits distinct mechanisms of action against inflammatory responses in biological systems. For example, the anti-inflammatory effects of phytogenic compounds, such as phenolics, flavonoids, and terpenes, are primarily attributed to their antioxidant activities, which neutralise ROS and enhance the activities of endogenous antioxidant enzymes such as SOD, CAT, and GPx (Basiouni et al., 2023). Likewise, phytobiotics regulate 5-lipoxygenase (5-LOX) activity, thereby reducing ROS generation and cytokine production (Yarla et al., 2016), thereby directly contributing to the downregulation of the inflammatory process. The bioactive compounds also regulate the eicosanoid balance by modulating cyclooxygenase-2 (COX-2) and 5-LOX activities, thereby reducing lipid peroxidation and decreasing prostaglandin production by inflammatory mediators (Mukhopadhyay et al., 2023).

Curcumin exhibits improved glutathione peroxidase (GSH-Px), catalase (CAT), and total superoxide dismutase (T-SOD) activities, resulting in improved Nrf2, Kelch-like ECH-associated protein 1 (Keap-1), heme oxygenase 1 (HO-1), and NAD(P)H quinone oxidoreductase 1 (NQO-1) gene expression in broiler birds (Zhang et al., 2024). An alternative mechanism involves its pathogen-inhibitory effects and the boosting of SCFA production, which fuels epithelial enterocytes in the intestinal mucosa (Abdelli et al., 2021). Likewise, tannins and saponins affect the intestinal mucosa and prevent pathogen adhesion, reducing enterotoxin production (Wang et al., 2023). Phytogenic substances have also been reported to enhance the structural and functional integrity of the intestine, reduce lesion scores associated with necrotic enteritis, and improve birds' resilience to heat stress (Oni & Oke, 2025).

Phytochemicals also modulate the inflammatory process by regulating specific protein and enzyme activities within biological modules. For instance, histone deacetylases (HDACs) and G-protein-coupled receptor 41 (GPR41/43) signalling, thereby reducing inflammation (Wang et al., 2024). Furthermore, oregano (thymol) inhibits NF-κB activation, reducing the replication of Gram-positive pathogens (Gago et al., 2025) and decreasing cytokine production (El-Sayed et al., 2024), thereby reducing the inflammatory response. Cinnamaldehyde suppresses pathogen quorum-sensing potential (Subhaswaraj et al., 2018), while curcumin activates Nrf2, leading to reduced COX-2 activity and pro-inflammatory cytokine production in poultry birds (Wu et al., 2021). Capsaicin modulates transient receptor potential vanilloid 1 (TRPV1)-mediated anti-inflammatory signalling in response to pathogens, thereby improving intestinal epithelial perfusion (Abdel-Salam & Mózsik, 2023). Citrus compounds such as limonene (β-pinene) target Nrf2, leading to reduced NF-κB activity and downregulation of oxidative stress (Rahayu et al., 2024). Sulphur-containing compounds (e.g., garlic) exert antioxidant and anti-inflammatory effects in poultry through Nrf2- and NF-κB-driven cytokine regulation (Rahayu et al., 2024).

Gene regulation in poultry is also reported to be mediated by the active ingredients of phytogenic compounds. For instance, cannabidiol increases the expression of genes that regulate gut integrity, thereby improving gut barrier function (Konieczka et al., 2020). Similarly, phenolic compounds in olive oil upregulate genes that maintain gut barrier integrity, strengthen tight junctions between intestinal cells, and reduce inflammation (Farràs et al., 2020). The mechanistic roles of phytogenic compounds and their bioactive components in the management of gut health for sustainable poultry production are illustrated in Fig. 1.

Fig. 1.

Mechanistic pathways of phytogenic compounds in enhancing gut health and sustainable poultry production.

6. Gut health and its functional properties

Poultry gastrointestinal health is a complex, dynamic system defined by intricate interactions among key determinants, including morphophysiological structures, resident microbiota, and nutrient availability. These interactions foster a supportive environment that boosts gut barrier integrity, strengthens immune function, and contributes to improved overall health and productivity (Celi et al., 2017; Clemensen et al., 2020; Aminullah et al., 2026). Gut health reflects the gut's structural and functional integrity, nutrient digestion and metabolism, immune response, and endocrine system through interactions among the gut microbiota, the brain, and the endocrine system (Berding et al., 2021). The gut microbiota balance in poultry directly impacts intestinal lining integrity, biological activities, and nutrient absorption. These factors collectively influence systemic immunity, neuroendocrine function, and overall productivity (Ferdous et al., 2019; Yue et al., 2025). During stress and infection, maintaining immune homeostasis is vital for gut health. The key components regulating intestinal function are gut barrier integrity, cytoprotection, and the management of inflammation (Mountzouris et al., 2020).

The intestinal epithelial cell barrier serves as an essential first line of defence and a physical barrier between the host's physiological system and the intestinal environment (Coleman et al., 2018). This epithelial barrier is protected by various chemical compounds secreted by goblet cells lining the intestinal villi. The protective barrier consists of two layers: an inner layer and an outer layer composed of mucopolysaccharides (Wickramasuriya et al., 2022). The inner layer is maintained as a sterile zone against microbial exposure by epithelial cells, whereas the outer layer provides a suitable platform for the commensal microbial population. Gut health is also regulated by antimicrobial peptides (AMPs), which play an important role as active agents that inhibit microbial invasion of the inner sterile layer and epithelial cells of the chicken intestine (Nazeer et al., 2021). Intestinal health sustainability depends on the dynamic integration of four types of barriers, including the microbiota and the physical, chemical, and immunological properties of the intestine, which can support the functional properties of the gut and hinder pathogen growth, toxin production, and the spread of other antigens (Robinson et al., 2015; Coleman et al., 2018). Studies have shown that other protective components, such as immunoglobulin A (IgA) and bioactive molecules produced by intestinal epithelial cells, diffuse into the inner layer, protecting the inner mucus from microbial adherence and inhibiting microbial translocation across the epithelium (Robinson et al., 2015). Research has demonstrated a complex interaction among dietary ingredients, the gut microbiota, and the nervous, immune, and endocrine systems, all of which can influence metabolic and gastrointestinal health. Imbalances or disruptions in this network can lead to mitochondrial dysfunction, which can adversely affect the gut microbiome and the immune system (Korniluk, 2017; Fung et al., 2017).

6.1. Intestinal microbiota

The microbiota in poultry intestines is a complex, ever-changing ecosystem that critically regulates birds' nutrition, immunity, and overall health. Gaining insights into its composition, functions, and influencing factors is vital for creating effective nutritional and management plans in contemporary poultry farming (Wickramasuriya et al., 2022). The poultry GIT harbors diverse microbial communities that vary by region, with the cecum being the most diverse and metabolically active compartment (Danlad et al., 2022). The gut microbiota primarily comprises four key phyla: Firmicutes, Bacteroidetes, Proteobacteria, and Actinobacteria. Their relative abundances fluctuate significantly across various intestinal segments and in response to dietary factors (Wang et al., 2021). The cecum shows greater microbial community diversity at the initial stage, then stabilises within two to three weeks at post-hatching age. This community is dominated by fermentative organisms, including Clostridia and other Firmicutes such as Subdoligranulum and Oscillospira, Bacteroidetes families such as Prevotellaceae, Proteobacteria such as Desulfovibrio, and various Actinobacteria (Richards et al., 2019). Conversely, the small intestine, especially the jejunum and ileum, has lower microbial diversity but actively responds to dietary supplements and probiotics, such as Lactobacillus species, often dominating the villus microbiota.

The intestinal microbiota is essential for nutrient absorption, metabolism, and the synthesis of short-chain fatty acids (SCFAs), which are important components of energy supply (Griela et al., 2021). The SCFAs, such as butyrate, propionate, and acetate, are produced from microbial fermentation of dietary fibre in the hindgut segment, serve as energy sources for colon cells, help maintain the epithelial barrier, and affect systemic health (Melaku et al., 2024). The microbiota play a crucial role in regulating mucosal barrier development, cytokine levels, and defence against harmful bacteria. SCFAs produced by fermentative taxa were associated with barrier gene expression and anti-inflammatory cytokine production in several intervention studies. The SCFAs regulate gut morphogenesis, including villus size and crypt depth, and physiological functions such as feed digestion, nutrient synthesis and absorption, and immune response (Aminullah et al., 2026; Azizi et al., 2026). Maintaining a stable microbiota can improve growth rates and feed efficiency, thus boosting productive performance in poultry (Naeem & Bourassa, 2025).

Several factors influence the composition and development of the poultry gut microbiota. The most well-documented drivers from recent studies include birds' age, diet composition, feed additives, and early microbial exposures (Fathima et al., 2022; Stanley & Yadav, 2022). During the first two to three weeks after hatching, microbial succession is marked by increasing Shannon diversity and community stabilisation, especially in the cecum. By around week three, the cecal community structure largely stabilises, as shown by research tracking succession dynamics using 16S rRNA sequencing and diversity analyses (Ahsan et al., 2018; Rubio, 2019). Dietary interventions and feed additives typically alter the relative abundances of existing taxa rather than introducing completely new phyla. Early-life interventions reduce opportunistic bacterial colonisation by Klebsiella and Enterococcus, leading to lower pro-inflammatory cytokine levels in cecal tonsils, indicating that early microbiota manipulation can help establish a positive immune environment (Sharma et al., 2026). Plant-derived additives uniquely influence microbiota composition. Tannin supplementation and fermented Chinese medicine residues altered cecal bacterial populations, increasing Szpirochaete and decreasing Prevotellaceae and Desulfovibrio. These shifts correlated with increased expression of tight junction proteins and decreased levels of inflammatory markers (Liu et al., 2023; Zhou et al., 2023). The functions of the poultry gut microbiota extend beyond colonisation resistance, playing central roles in host metabolism, immune regulation, and physiological homeostasis.

The composition of the gut microbiota is also affected by the type and level of phytogenic feed additives used in poultry. Different plant tannins had specific effects on microbiota composition, immune responses, and antioxidant endpoints, whereas fermented Chinese medicine residues altered cecal taxa and decreased bacterial abundance in the cecum (Zhou et al., 2023). Recent trials comparing various tannins or fermented residues used 16S sequencing alongside performance, antioxidant, and immune markers to demonstrate source-dependent effects on microbiota and hosts. These findings highlight that different natural feed additives generate distinct microbial profiles, leading to specific functional responses in the host (Li et al., 2023). These studies demonstrate progress toward establishing causal relationships among microbial taxa, metabolites, and host performance and immunity using targeted omics methods. Combining microbial profiling with functional assessments provides a mechanistic understanding of how dietary changes modify the gut ecosystem, yielding tangible gains in growth, health, and production efficiency in poultry. Lactobacilli colonisation in the intestine decreases the expression of pro-inflammatory cytokines such as interferon-gamma (IFN-γ), interleukin-1 beta (IL-1β), and interleukin-8 (IL-8) in cecal tonsils. This suggests that manipulating the microbiota in early life can reduce inflammation and support immune system balance (Sharma et al., 2026). Tannin supplementation decreases IL-1β levels and increases IL-10 in serum; some tannins also lower interleukin-6 (IL-6) and TNF-α (Liu et al., 2023).

6.2. Phytogenic and gut health

Phytobiotics primarily work by modulating the gut ecosystem (Mountzouris et al., 2020), helping to maintain the integrity of the gut epithelial barrier through both direct and indirect mechanisms. The direct pathway involves enhancing tight junction assembly, which protects the gut barrier from deleterious molecules and toxic metabolites. Conversely, the indirect pathway involves the downregulation of Toll-like receptor (TLR) signalling and the subsequent suppression of NF-κB pathway activation (Paraskeuas & Mountzouris, 2016). Additionally, phytobiotics have the potential to exhibit antimicrobial activity against both Gram-positive and Gram-negative bacteria (Kiczorowska et al., 2017), thereby affecting gut health. It has been reported that a combination of phytobiotics, such as oregano, cinnamon, and clove oils, together with inulin, beta-glucans, and ascorbic acid, can serve as an effective alternative to salinomycin. This combination improves gut health and production performance in broilers challenged with Eimeria spp (Galamatis et al., 2025). The effects are attributed to enhanced antioxidant enzyme activity and reduced pathogen load and gut inflammation, resulting in an improved microbiome, enhanced gut integrity, and improved nutrient digestion and absorption.

This study suggests that phytogenically derived active compounds can promote gut barrier integrity, exert antimicrobial effects, reduce intestinal pathogen load, and maintain gut health, thereby improving poultry growth performance and productivity.

6.3. Phytogenic and gut morphogenesis

Gut morphogenesis is a dynamic process regulated by pattern recognition receptors (PRRs), antimicrobial peptides (AMPs), secretory IGA, and resident microbiota (Chen et al., 2025). Phytogenic feed additives markedly influence the development and morphological structure of the poultry GIT. Gut villus height, villus-to-crypt ratio and crypt depth and mucosal layer thickness can be improved by a phytogenic source (Euphorbia hirta) in broiler birds (Hashemi et al., 2014). The villus height-to-crypt depth (VH: CD) ratio is an effective, practical proxy for enhanced mucosal maturity and reduced inflammatory responses. These structural changes occur through coordinated cellular and molecular regulatory mechanisms, including enterocyte proliferation and differentiation, goblet cell activity, tight junction formation, and regulation of inflammatory and growth signalling pathways (Oni & Oke, 2025).

The impact of PFAs on gut development varies with the type of bioactive molecules, the dosage used, and the intestinal segment, with specific patterns consistently altering intestinal structure to enhance absorptive surface area and functional capacity (Wang et al., 2021). Increases in villus height have been observed with chlorogenic acid supplementation at 1.5 g/kg in the ileum between 28 and 42 days of age, as well as with various essential oil formulations in the duodenum, jejunum, and ileum (Ali et al., 2024; Li et al., 2023). These increases in villus height expand the epithelial surface area for nutrient absorption and are usually associated with enhanced digestive enzyme activity and increased expression of nutrient transporters. Improvements in the villus-to-crypt ratio were observed with the administration of microencapsulated essential oils and organic acids at doses of 200-400 mg/kg. Notably, duodenal lipase activity was enhanced by supplementation with 20-600 mg/kg of essential oils and organic acids, suggesting improved digestive capacity (Huang et al., 2024). Mechanistic morphological outcomes depend on the type of phytogenic, the bioactive component, and the dose used, often correlating with enhanced expression of genes involved in nutrient transport and improved growth performance (Li et al., 2023). Bitter phytogenics, such as saponins, modulate bile acid production and microbial transformations of bile acids, thereby promoting agonism at FXR/TGR5. The receptors promote barrier gene expression, maintain fluid balance, and improve enterocyte formation in the intestine (Peng et al., 2025). Phytogenics modulate enterocyte dynamics and tight junction composition, leading to overall epithelial integrity by coordinating various cellular mechanisms, leading to improved growth factor signals associated with epithelial growth (Guo et al., 2025). Additionally, there was a notable increase in MUC2 expression, a crucial secretory mucin in intestinal goblet cells, following supplementation with a thymol-carvacrol eutectic. Flavonoids can upregulate MUC2 transcription, resulting in enhanced mucus thickness and quality, leading to an increased number of goblet cells that support villus tips, reduce injury stress, and activate pathogen decoys (Wang et al., 2025).

These findings indicate a strengthened mucus barrier and improved mucosal defence mechanisms (Dong et al., 2024a). The mucosal layer serves as an essential first barrier against pathogens while also maintaining a moist environment, which is crucial for nutrient absorption and microbial growth. Tight junction proteins, which play a crucial role in regulating paracellular permeability and maintaining epithelial barrier integrity, are consistently upregulated by various phytogenic treatments. Additionally, preparations of essential oils and organic acids have been shown to enhance the expression of claudin-1 and ZO-1, with specific essential oil blends also notably increasing occludin levels in the ileal mucosa (Huang et al., 2024; Li et al., 2023). These cellular changes collectively explain the observed morphological features, such as increased villus height, higher villus-to-crypt ratios, reduced crypt hyperplasia, and enhanced nutrient absorption and barrier function in experimental models (Izadi, 2025).

An essential oil and organic acid blend have been shown to increase IGF-2 mRNA expression in the jejunum, thereby linking PFAs to conventional epithelial growth and trophic signalling pathways (Pham et al., 2022). Additionally, microencapsulated essential oil formulations enhance digestive enzyme activity, upregulate the expression of tight junction proteins such as claudin-1 and ZO-1, elevate levels of IL-10 and antimicrobial peptides, and result in a reduction of ileal crypt depth, an improved villus-to-crypt ratio, increased duodenal lipase activity, and improved early growth performance (Huang et al., 2024). Furthermore, increased expression of tight junction genes such as ZO-1, claudin-1, and occludin, as well as mucin-2, has been observed in small intestinal segments following dietary sodium butyrate supplementation in avian subjects. This molecular alteration was associated with enhanced villus morphology and reduced inflammatory responses. Additionally, phytogenic bioactive compounds, including tannins and fermented residues, have been shown to upregulate tight junction protein expression and to positively influence the villus height-to-crypt depth ratio in the jejunum and ileum of broiler chickens (Zhou et al., 2023).

6.4. Phytogenic and gut physiological functions

Phytogenics play an important role in regulating various facets of poultry gut health, including digestive enzyme activities, nutrient absorption efficiency, barrier integrity, and inflammatory responses. The response mechanisms are mediated by molecular targets such as pattern recognition receptors, transcription factors, and metabolic enzymes, with effects that depend on the compound class, formulation, and dosage (Pham et al., 2023). Phytogenics influence enzyme activities and gene expression in the avian digestive tract through hormonal and transcriptional mechanisms. Several studies have demonstrated upregulating of pancreatic enzyme related genes and increased luminal enzyme activity in poultry feed containing phytogenic compounds. These changes correlate with increased digestive capacity and improved feed efficiency in poultry (Shehata et al., 2022). Mechanistically, dietary-sourced eugenol nanoemulsion increases the expression of pancreatic and related digestive enzymes genes such as pancreatic amylase (AMY2A), lipase (PNLIP), chymotrypsin-like elastase family member 1 (CELA1), and the enteroendocrine hormone cholecystokinin (CCK), resulting in enhanced pancreatic secretion and enzymes production (Ibrahim et al., 2022). Laying hens supplemented with oregano essential oil have been shown to increase chymotrypsin and lipase activities, suggesting improved proteolytic and lipolytic functions at the intestinal lumen (Feng et al., 2021). Improved jejunal morphology, such as increased villus height, along with enhanced nutrient absorption, supports the mechanistic approach proposed by Alharbi et al. (2022), suggesting that phytogenic compounds induce mucosal maturation, which in turn improves brush-border function (Murugesan et al., 2015). In addition, studies demonstrate increased expression of tight junction proteins, such as claudin-1, occludin, and ZO-1, when phytogenic or essential oils are used, resulting in improved barrier function and reduced epithelial weakness in the intestinal lumen. Certain phytobiotics stimulate growth factors, including EGF, IGF-1, and trefoil factors (TFF3), thereby improving the restoration rate of crypt cell cycling and enhancing villus elongation after stress or pathogen challenge (Akdemir Evrendilek, 2026). Eugenol nanoemulsion directly enhances the expression of genes encoding digestive enzymes and improves overall performance (Ibrahim et al., 2022). The villus height and function are regulated by certain polyphenolic compounds, including rosmarinic acid, carvacrol, thymol, and catechins, through specific molecular mechanisms. The PFAs bioactive molecules activate Nrf2-ARE signalling, thereby inducing phase II enzymes such as HO-1, NQO1, and GCLC. This progression limits oxidative damage to sensitive molecules, including DNA, and preserves the ISC niche, thereby increasing villus height (Alharbi et al., 2022). This enlargement correlates with improved apparent digestibility of nutrient extracts in birds (Feng et al., 2021; Liu et al., 2026). Both eugenol nanoemulsion and the combination of essential oil with organic acids significantly upregulate fatty acid-binding protein 2 (FABP-2) mRNA expression, indicating enhanced cytosolic lipid trafficking in enterocytes, which may facilitate increased lipid absorption and metabolism (Ibrahim et al., 2022; Huang et al., 2024).

Additionally, citrus extract elevates poultry cecal short-chain fatty acids such as acetate and butyrate (Yu et al., 2019), activates GPR41/43/109A gem on epithelial and immune cells, and promotes epithelial energy metabolism and anti-inflammatory activities (Niu et al., 2026). It concurrently reduces proteolytic fermentation by-products. This metabolic profile contributes to epithelial health and may indirectly facilitate nutrient absorption through its trophic and anti-inflammatory properties (Yu et al., 2019). Trans-anethole reduced serum diamine oxidase activity and D-lactate concentrations, both of which serve as systemic biomarkers of mucosal injury and increased intestinal permeability. Moreover, it increased the number of proliferating cell nuclear antigen (PCNA)-positive enterocytes. It increased the villus height-to-crypt depth ratio, suggesting reduced intestinal leakiness and enhanced epithelial regeneration (Yu et al., 2022).

The active ingredients of phytogenic also affect gene expression and alter functional capabilities and potential in poultry. The rise in AMY2A and protease-related gene expression following phytogenic administration suggests improved starch and protein breakdown in the lumen prior to absorption by brush border and enterocytes (Ibrahim et al., 2022). Furthermore, the phytogenic compounds were demonstrated to suppress the expression of toll-like receptors (TLRs) and reduce the activity of the downstream NF-κB signalling pathway. This involves lower levels of TLR-4 and TLR-2, and decreased NF-κB translocation, providing mechanistic insight into how reduced mucosal inflammation preserves tight junctions and promotes mucin production (Abd El-Hamid et al., 2024). These molecular and cellular changes correspond to reduced pathogen loads and improved resistance to enteric challenges, including reduced expression of virulence genes in Salmonella and Escherichia coli, linking barrier reinforcement to reduced luminal pathogen translocation (Murugesan et al., 2015).

The bioactive compounds in phytogenics also affect intestinal lining protectants, which shield the gut epithelial layer from pathological changes, thereby improving gut health. For example, thymol and carvacrol eutectic at doses ranging from 30 to 120 mg/kg, with an optimal concentration of 30 mg/kg, have been shown to improve jejunal morphogenesis, increase the expression of MUC2 and occludin mRNA, enhance nutrient absorption and transport capabilities, as well as upregulate anti-inflammatory IL-10 expression (Y. Li et al., 2023). Similarly, oregano essential oil administered at doses of 100-400 mg/kg, with 200 mg/kg identified as the optimal dose, demonstrates significant effects, including increased chymotrypsin and lipase activities, elevated ZO-1 levels, decreased pro-inflammatory cytokines, and modifications in ileal microbiota composition (Ruan et al., 2021). Moreover, coated essential oils and organic acids within the dosage range of 300 to 800 mg/kg consistently upregulate tight junction proteins such as claudin-1, occludin, ZO-1, and MUC-2, while downregulating TLR-4 expression; these compounds also enhance fatty acid metabolism pathways and promote the proliferation of butyrate-producing bacteria, further contributing to gut health (Huang et al., 2024). Bioactive components of plant origin modulate intestinal functions through enteroendocrine signalling and nutrient sensing. The bioactive molecules engage intestinal GPCRs (TAS1R and TAS2R families) and TRP channels (TRPA1 and TRPV1), triggering the release of GLP-1, GLP-2, PYY, and CCK. GLP-2 improves mucosal growth, enhances the TP repair process and crypt-villus modulation, whereas CCK and PYY coordinate motility and digestive secretions that form the morphogenic process (Grau Bové, 2021). In addition, trans-anethole, administered at a 400 to 600 mg/kg dietary level with an optimal dose of 600 mg/kg, exerts anti-inflammatory effects by inhibiting NF-κB translocation, strengthening tight junction integrity, and increasing levels of PCNA and secretory IgA (sIgA), in addition to reducing D-lactate, diamine oxidase, and pro-inflammatory cytokines (Yu et al., 2022). Citrus extract at a 10 mg/kg diet supplementation level increases the abundance of Bifidobacterium and Lactobacillus, elevates cecal acetate and butyrate concentrations, and upregulates the expression of the tight junction proteins ZO-1 and claudin, collectively contributing to improved intestinal barrier function (Yu et al., 2019).

Collectively, these studies underscore the presence of non-linear dose-response relationships, with medium or specifically low doses offering optimal benefits. This highlights the critical importance of narrow therapeutic windows and formulation considerations in ensuring stability and palatability (Dong et al., 2024b; Murugesan et al., 2015; Yu et al., 2022). Formulations designed to enhance stability and absorption, such as nanoemulsions for eugenol and eutectic or cocrystal techniques for thymol and carvacrol, have been shown to improve biological effects and efficiency by increasing availability (Feng et al., 2021). The observed upregulation of enteroendocrine CCK expression, coupled with the induction of pancreatic enzyme genes, provides compelling evidence that phytogenics effectively activate enteroendocrine-to-exocrine pathways, thereby modulating pancreatic secretion (Dong et al., 2024a). Moreover, the coordinated regulation of digestive enzymes, enhanced nutrient absorption, strengthened barrier integrity, and reduced inflammatory responses collectively indicate that phytogenic compounds exert multifaceted effects on physiological systems, contributing to improved gut health and overall performance in poultry. The phytogenic dose- and formulation-dependent effects underscore the importance of optimising phytogenic supplementation strategies tailored to specific compound types, delivery methods, and production contexts.

7. Effect of phytogenics on gut health

Phytogenics contain various bioactive compounds that demonstrate diverse effects on the morphological structure, barrier integrity, strength and physiological functions of poultry intestine. The key PFAs, their bioactive components, dosages, and impacts are categorically summarised in Table 2.

Table 2.

The phytogenic effect-based classification, their bioactive components and dosage for sustainable poultry production.

Phytogenic	Bioactive molecule/compound	Dosage used	Effect	Reference
Phytogens exhibit morphological effects
Essential oils	Oregano, cinnamon, inulin, and beta-glucans	1 gm/kg diet	Improved intestinal morphology; compensatory response to epithelial barrier disruption	(Galamatis et al., 2025)
Mushroom stem	Ganoderma lucidum (reishi), Hericium erinaceus (lion's mane), Lentinula edodes (shiitake), Pleurotus ostreatus (oyster)	30 gm/kg diet	Improves the histological structure of the cecum, villi height, width, and their perspective ratio	(Nasir et al., 2024)
Cinnamon bark essential oil	Trans-Cinnamaldehyde Eugenol & Eugenyl Acetate Cinnamyl Acetate & Caryophyllene	300 mg/kg diet in broilers	Improved the immunological response Improved the height of intestinal villi Increased the serum SOD	(Al-Abdullatif et al., 2023)
Origanum vulgare, Cinnamomum verum, citric acid, and malic acid	Thymol and carvacrol	1 ML/4 L of drinking water	The small intestine villus height and villus-height-to-crypt-depth ratio improved	(Zeeshan et al., 2022)
Phytogenic blend in Clostridium perfringens-infected broiler birds	Essential oil from carvacrol, cinnamaldehyde, capsaicin from paprika, essential oil of thyme, and anise yucca extract cinnamaldehyde		The intestinal villus height and width increased significantly	(Abudabos et al., 2018)
Phytogenic blend	Alpha-acids & Beta-acids Prenylated Flavonoids (Xanthohumol & Isoxanthohumol) Glycyrrhizin Glabridin & Liquiritigenin	200 mg/kg diet	Improved the gut morphogenesis parameters such as intestinal wall thickness, crypt depth, and the villus height to crypt depth ratio	(Szkopek & Michalczuk, 2020; Alagawany et al., 2019)
Essential oils from oregano	Thymol and carvacrol eutectic	30 mg/kg diet	Enhanced jejunal function and transport capacity	(L. Li et al., 2023).
A commercial blend of phytogenic compounds, such as aerial parts of Cynodon dactylon, Aerva lanata, black pepper (Piper nigrum), and Piper betle leaves	Phenolic acids, flavonoids, phytol, thymol, eugenol, and piperine were quantified in the mixture	1 and 2% in the diet	Increased the height of the duodenum and jejunum villus	(Oso et al., 2012)
Phytogenic	Bioactive molecule/compound	Dosage used	Effect	Reference
A commercial blend of cinnamon 20 g, cumin 20 g, peppermint oil 170 g, garlic oil 150 g, anise oil 50 g, fennel oil 40 g per kg, with SiO2 and NaCl as carriers.	Allicin, linalool, piperine, allyl-isothiocyanate, anethole, cineole, carvacrol, capsaicin, and thymol	100, 125, and 150 mg/kg diet	•Improved the villus length, width, and thickness. •Reduced the crypt depth and goblet cell number per villus in birds compared to those fed control diets.	(Oni & Oke, 2025)
Phytogenic commercial mixture (Digestarom®, Poultry Biomin Holding GmbH, Austria)	Premix of more than 30 essential oils and bioactive compounds	150 mg/kg diet	•Improved villus height in the small intestine •Enhanced villus height and lowered crypt depth	(Murugesan et al., 2015)
Taraxacum mongolicum extract,	Polyphenols and flavonoids were used at 500- 2000 mg/kg,	with 1000 mg/kg optimal	•Higher duodenal villus-to-crypt ratios, increased ileal occludin,	(Dong et al., 2024b).
Blend of thymus vulgaris and Filipendula ulmaria, Ginkgo biloba and Silybum marianum	Flavonoid Glycosides, Terpenoids (Ginkgolides & Bilobalide, flavonolignans, Thymol	100 and 200 mg/kg 100 and 300 mg/kg diet	•Both the composition and dosage affected villus height, crypt depth, and their ratio	(Ceylan et al., 2025; Biernacka et al., 2023; Bijak, 2017)
Essential oil	Thyme (4%), carvacrol (4%), hexanoic acid (0.5%), benzoic acid (3.5%), and butyric acid (0.5%)	500 mg/kg diet	•Improved villus and villus height/crypt depth ratio.	(Pham et al., 2020)
Thyme and star anise-sourced essential oil.	Thymol and anethole are the lead active components	150 and 1500 mg/kg diet	•Decreased goblet cells in the jejunum •In the proximal ileum, lowered crypt depths •In the distal ileum, the villus height: crypt depth ratio was higher in birds fed the PFAs at the 150 ppm level	(Humer et al., 2015)
Essential oils	Thymol and anethole	150 mg/kg diet	•Increased the villus height to crypt depth ratio in the intestinal jejunum segment	(Amad et al., 2013)
Blend of: Grape seed extract, Chinese cinnamon essential oil, fenugreek seeds, Chilean boldo leaves, turmeric extract, citrus extract and Trigonella foenum-graecum	Curcuma longa, Cinnamomum zeylanicum, Peumus boldus	700 mg/kg (1-10 days) 500 mg/kg (11-21 days) 300 mg/kg (21-35 days)	•The pH values of jejunum contents were reduced. •The villus height and crypt depth were improved in birds fed the alternative from day 7th	(Fascina et al., 2017)
Phytogenic	Bioactive molecule/compound	Dosage used	Effect	Reference
Phytogenics exhibit physiological effects
Phytogenic commercial mixture (Digestarom®, Poultry Biomin Holding GmbH, Austria)	Premix of more than 30 essential oils and bioactive compounds	150 mg/kg diet	•Decreased the total load of anaerobic bacteria, Clostridium spp., and coliform, while supporting the Lactobacillus spp.	(Murugesan et al., 2015)
Essential oil	Thyme (4%), carvacrol (4%), hexanoic acid (0.5%), benzoic acid (3.5%), and butyric acid (0.5%)	500 mg/kg diet	•Suppressed the intestinal C. perfringens colonisation, liver C. perfringens formation, and gut lesion scores.	(Pham et al., 2020)
Essential oils	Thymol, carvacrol, cinnamaldehyde, and thyme oil	150 ppm, 300 ppm, 300 ppm, and 600 ppm, respectively	•Strong antimicrobial effects on Escherichia coli	(Axmann et al., 2021)
Oregano essential oil	Carvacrol, Thymol, Para-c-Cymene, γ-Terpinene and β-Caryophyllene	200 mg/kg diet	•Boosts chymotrypsin and lipase activities in a dose-dependent manner	(Feng et al., 2021)
Lemongrass and rosemary	Citral, terpenoids, carnosic acid, and carnosol, as well as rosmarinic acid,	1% in the diet	•Lowered Escherichia coli •Increased Lactobacillus	(Engida et al., 2023)
A blend of: Origanum vulgare Thyme, Oregano, and Caraway	Carvacrol, thymol, carvone, methyl salicylate, and menthol	150 mg/kg diet	•With reduced dietary protein and energy intake, the gut antioxidant capacity improved	(Griela & Paraskeuas, 2021)
Commercial phytogenics blend	Essential oils sourced from oregano, anise, and citrus, and fructooligosaccharides	125 mg/kg diet	•No effect on villus height or villus surface area, but reduced the villus/crypt ratio •Concluded that phytogenics are not directly involved with changes in gut barrier integrity, but are connected with other physiological mechanisms	(Perić et al., 2010)
A commercial blend of phytogenic compounds, such as aerial parts of Cynodon dactylon, Aerva lanata, black pepper (Piper nigrum), and Piper betle leaves	Phenolic acids, flavonoids, phytol, thymol, eugenol, and piperine were quantified in the mixture	1 and 2% in the diet	•Bifidobacterium concentration of the cecum content showed a slight increase	(Oso et al., 2012)
Blend of: Grape seed extract, Chinese cinnamon essential oil, and fenugreek seeds, Chilean boldo leaves, turmeric extract, citrus extract and Trigonella foenum-graecum	Curcuma longa, Cinnamomum zeylanicum, Peumus boldus	700 mg/kg (1-10 days) 500 mg/kg (11-21 days) 300 mg/kg (21-35 days)	•The pH values of jejunum contents were reduced	(Fascina et al., 2017)

8. The PFAs optimal dosage ranges

The dose-response curve of PFAs in poultry is generally non-linear, often showing an inverted-U or plateau pattern (illustrated in Table 2). Research indicates that the ideal dose varies with factors such as plant source, extraction method, formulation, bird age, and environmental stress (Nurzyńska-Wierdak, 2023). In general, moderate doses tend to improve growth, gut health, and immunity, whereas higher doses may impair nutrient absorption, cause liver toxicity, or disrupt beneficial microbiota. Encapsulated formulations typically require lower doses than convention formulations, underscoring the importance of delivery technique. However, despite the high variability, Table 3 presents the reported optimum PFAs doses for poultry production.

Table 3.

Recommended optimal dosage ranges for major phytogenic feed additive classes in poultry.

Phytogenic compound	Recommended optimal dose	Method of administration	References
Thymol + carvacrol (encapsulated essential oils)	100 mg/kg	Dietary	(Lee et al., 2020)
Carvacrol essential oil	300-400 μL/day	Orally at 18:00 hr	(Liu et al., 2018)
Carvacrol + thymol + cinnamaldehyde (blend)	0.5%	Dietary	(Reis et al., 2018)
Encapsulated cinnamon, thyme, clove oils	Dietary	(Madkour et al., 2025)
Oregano essential oil	300 ppm	Dietary	(Mohiti-Asli & Ghanaatparast-Rashti, 2017, 2018)
Moringa oleifera leaf extract	90-120 mL/L	Dietary	(Jan et al., 2025)
Cinnamaldehyde + quercetin + 7-hydroxycoumarin	Combined blend	Dietary	(Kurilkina et al., 2026)
Lavender + eucalyptus + pine oil blend	100 ppm	Drinking water	(Merdana et al., 2024)
Eucalyptus globulus oil	200 mg/kg	Dietary	(Ji et al., 2026)
Essential oil blend (eucalyptus, citrus, thymol, bromohexine)	0.30 mL/kg	Dietary	(Khan et al., 2024)
Thyme essential oil + postbiotic	0.2%-0.3%	Dietary	(Doski & Kareem, 2023)

9. Phytogenics implications in sustainable production

The global poultry sector faces mounting pressure to increase productivity while reducing environmental impacts and antimicrobial use, heightening interest in plant-derived feed additives as sustainable alternatives to antibiotics (Azizi et al., 2024a; Mnisi et al., 2024). Public health concerns about antimicrobial resistance linked to antibiotic use in poultry production have shifted research toward phytogenic feed additives, given their multifunctional biological effects and lower risk of promoting resistance (Zahir et al., 2026). Beyond their health benefits, phytogenic supplementation also enhances growth performance and overall productivity in poultry, supporting improved body weight gain at appropriate inclusion levels (Aminullah et al., 2026). Similarly, in another study, dietary supplementation with 0.25-1.25% brown or green seaweed improved broiler growth performance and nutrient digestibility, while 0.50-0.75% green seaweed enhanced hepatic GHR and IGF-1 gene expression, indicating improved nutrient utilisation (Azizi et al., 2024b).

Mechanistically, phytobiotics such as essential oils, tannins, saponins, and flavonoids modulate gut microbiota succession and strengthen mucosal integrity, thereby optimizing digestive enzyme activities (Obianwuna et al., 2024) and improving feed conversion ratios and daily weight gain in commercial farming systems. Phytogenic bioactive compounds enhance poultry meat quality by boosting volatile fatty acid profiles, oxidative stability, and shelf life, thereby reducing post-production losses and improving supply-chain efficiency (Michalczuk et al., 2024), thereby improving sustainability. They also support market sustainability, as consumers' perceptions increasingly favor plant-based additives and natural production systems, thereby enhancing acceptance and product value (Aminullah et al., 2025; Azizi et al., 2026). Furthermore, phytogenic additives support environmental sustainability in the poultry production cycle by improving nutrient utilization, reducing nitrogen and phosphorus excretion, and lowering ammonia emissions, thereby aligning poultry systems with broader climate-resilient livestock goals (Mnisi et al., 2024; Oni and Oke, 2025b; Wang et al., 2024), increasing safety and reducing antibiotic reliance, leading to the offer of organic products promising for public health (Nhara et al., 2025; El-sabrout et al., 2026). From a socio-economic perspective, phytogenic additives promote sustainability by using locally available plant resources, reducing reliance on imported pharmaceuticals, supporting regional agricultural economies, and enhancing resilience in low-income poultry systems (Mnisi et al., 2024; Obianwuna et al., 2024).

However, the practical sustainability of phytogenic feed additives extends beyond their environmental and health benefits and must also be evaluated for economic feasibility and commercial applicability. Although phytogenic additives can improve productivity and bird health, their large-scale adoption may be constrained by the costs associated with sourcing plant materials, extraction and purification technologies, product standardization, and formulation processes required to ensure consistent efficacy (McGurrin et al., 2025). Consequently, the economic return of phytogenic supplementation depends on whether improvements in feed efficiency, flock health, product quality, and production performance are sufficient to offset the additional costs incurred by producers.

Another important consideration is the transition from conventional antimicrobial growth promoters to phytogenic-based strategies. While phytogenic additives offer a promising alternative to antibiotic-dependent production systems, their performance is often influenced by multiple interacting factors, including bird genetics, health status, diet composition, environmental stressors, pathogen challenge, and farm management practices (Nantapo and Marume, 2025; Obianwuna et al., 2024). Consequently, the magnitude of performance improvements observed under controlled experimental conditions may not always be replicated under commercial field settings. This variability underscores the importance of precision-based nutritional approaches that optimize phytogenic formulations, inclusion levels, and delivery systems for specific production environments.

Integrating phytogenics into the production cycle through a science-driven, data-informed, precise nutritional strategy and formulation enables dose optimization and reduces greenhouse gas intensity per kilogram of live weight. The heterogeneity of bioactive compounds in phytogenics and inconsistent trial methodologies remain challenges (Rodriguero et al., 2026). Developing robust meta-analytic evidence, standardized quality criteria, and on-farm monitoring for responsive supplementation can position phytogenics as a key component of circular, low-antibiotic poultry production, balancing economic viability with environmental safety. The interconnected benefits, challenges, and enabling factors associated with phytogenic feed additives in sustainable poultry production are summarized in Fig. 2.

Fig. 2.

Phytogenics implications in sustainable poultry production. Source: Authors' illustration based on information synthesized from the literature cited in this section.

10. Phytogenic limitations in poultry production

The commercial implementation of phytogenic-based feeding programs also presents challenges related to scalability and product consistency. The effectiveness of phytogenic additives depends on the concentration and stability of their bioactive compounds, which can vary according to plant genotype, geographical origin, environmental conditions, harvesting stage, storage conditions, and extraction methods (Engida et al., 2023; Obianwuna et al., 2024), environmental and experimental challenges, and animal characteristics, etc. (Abdelli et al., 2021). Such variability may affect product quality and potentially contribute to inconsistent responses among studies and commercial production systems. Furthermore, successful large-scale applications require reliable raw material supply chains, standardized manufacturing protocols, and effective quality-control measures to maintain the stability and bioavailability of active compounds during feed processing and storage (Wang et al., 2024). Advances such as microencapsulation and controlled-release systems protect bioactive compounds and deliver them to the intestine for maximum effect (Mnisi et al., 2024; N. Wang et al., 2024). As a strategic approach, the standard formulation of phytogenic blends with defined active constituents is important. It should be supported by an optimal harvest stage, standardized processing methods, and appropriate dosing (Cojocariu et al., 2026). These factors should also be adjusted to the birds' physiological stage. Such optimization helps stabilize performance outcomes and reduce variation across flocks and feed matrices throughout the production period (Oketch and Heo, 2026). Therefore, future research should extend beyond efficacy assessments and place greater emphasis on commercial-scale validation, long-term field studies, and comprehensive cost-benefit analyses. Generating robust evidence under practical production conditions will strengthen producer confidence, improve adoption rates, and facilitate the integration of phytogenic feed additives as economically viable and sustainable alternatives to conventional antimicrobial growth promoters.

11. Study limitations

Insufficient availability of literature that meets our study's selection criteria may have led to selection bias. Likewise, commercial interests in PFAs may have led to the publication of favourable findings, while underreporting of negative or null results automatically leads to positive-result bias. To achieve a comprehensive perspective and the most valid study, the limited availability of recently published, in-depth studies was an additional important factor that hindered our study. In addition, the inconsistency in PFAs' effects across the literature in poultry production was a challenge for the critical conclusions of this study.

12. Conclusion

Phytogenic feed additives offer a promising, multifaceted nutritional strategy to improve poultry gut health and support sustainable production systems. The diverse bioactive compounds in phytogenics exert antioxidant, antimicrobial, and anti-inflammatory effects, collectively enhancing intestinal integrity, modulating the gut microbiota, and improving digestive efficiency. By regulating tight junction proteins, enhancing digestive enzyme activity, and stimulating the production of beneficial microbial metabolites, such as short-chain fatty acids, phytogenics improve nutrient utilization, immune competence, and overall growth performance in poultry. These properties make phytogenic compounds viable alternatives to antibiotic growth promoters in modern poultry production. Nevertheless, the efficacy of phytogenics can vary by plant origin, extraction methods, formulation, and dosage levels, highlighting the need for standardization and precise nutritional strategies. Future research integrating omics-based approaches, controlled feeding trials, and advanced delivery systems, such as microencapsulation, will further clarify mechanisms of action and optimize their practical applications. With continued scientific validation and standardization, PFAs have strong potential to play a central role in developing resilient, environmentally sustainable, and antibiotic-reduced poultry production systems.

Ethical statement

Veterinary and Animal Science

This review article does not involve any studies with human participants or animals performed by any of the authors.

Funding

The authors did not receive any financial support for this research, authorship, or publication.

CRediT authorship contribution statement

Noor Aminullah: Writing – review & editing, Writing – original draft, Visualization, Validation, Conceptualization. Faisal Danish: Writing – review & editing, Writing – original draft, Visualization, Validation. Ahmadullah Zahir: Writing – review & editing, Writing – original draft, Visualization. Mohammad Naeem Azizi: Writing – review & editing, Writing – original draft, Visualization, Validation.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data availability

This study did not involve the creation or analysis of any datasets.