Oxidative stress is one of the most important factors affecting health and productive performance in poultry, primarily due to exposure to environmental stressors such as high temperatures, high stocking density, and pathogenic problems. Oxidative stress results in the production of reactive oxygen species (ROS), causing biomolecular damage such as lipid peroxidation, protein oxidation, and DNA damage (Han & Lee, 2022).

Phytobiotics provide beneficial effects in these situations through two main pathways: direct and indirect antioxidant actions. Directly, flavonoids and polyphenols serve as free radical scavengers by giving electrons to stabilize ROS, thus preventing free radical chain reactions (Bas, 2026). Phytobiotics also regulate the endogenous antioxidant defense system indirectly by activating molecular pathways, especially the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway. This pathway plays a crucial role in the regulation of redox balance, detoxification activities, and modulation of the immunological response of host cells. Under oxidative stress, the activation pathway is triggered by dissociation of Nrf2 from its cytoplasmic inhibitor, Kelch-like ECH-associated protein 1 (Keap1). Following release, Nrf2 translocates to the nucleus and upregulates the expression of antioxidant genes such as glutathione peroxidase (GPx), superoxide dismutase (SOD), and catalase (CAT) (Kikusato, 2021);(Ma et al., 2021).

Phytobiotic supplementation has been shown to increase the activity of antioxidant enzymes in several investigations. For instance, (Zhang et al., 2018) and (Zhang et al., 2015) observed that treatment of heat-stressed broilers with curcumin resulted in decreased malondialdehyde (MDA) levels and increased SOD and GPx activity via activation of the Nrf2 pathway. Similarly, (Shen et al., 2019) reported that the bamboo leaf extract rich in polyphenols in the diet enhanced the overall antioxidant capacity of breast meat via Nrf2 activation. Green tea extract is a catechins source, especially epigallocatechin gallate, which has similarly been shown to increase the activity of antioxidant enzymes and defend tissues against oxidative damage (Simoni et al., 2025). Essential oils from thyme and oregano are rich in carvacrol and thymol, which also play important roles in the antioxidant system. These compounds significantly increased total antioxidant capacity, superoxide dismutase, and glutathione peroxidase activities by up to approximately 141%, 24%, and 122%, respectively, and decreased malondialdehyde concentration by up to approximately 61% during the peak laying phase in laying hens (Johnson et al., 2025). Moreover, it has been reported that rosemary extract rich in rosmarinic acid and carnosic acid increases plasma antioxidant activity and improves redox status in poultry under oxidative stress (Sierżant et al., 2021). This demonstrates the close and reciprocal relationship between the antioxidant system and immune system. Increased oxidative stress leads to activation of inflammatory pathways and suppression of immune function, and increased antioxidant capacity may help to decrease inflammation and boost immune responses. Thus, phytobiotics with antioxidant and immunomodulatory activities have synergistic effects on the maintenance of physiological homeostasis of poultry. Additionally, several studies have demonstrated that phytogenic blends may exert stronger effects than single-compound supplementation due to synergistic interactions of bioactive compounds (Murwani et al., 2024)

Phytobiotics have significant immunomodulatory effects in addition to their antioxidant activity. The immune system of poultry consists of a cellular and a humoral immune system, which work synergistically to combat pathogens. Phytobiotics are known to improve humoral immune responses through enhanced production of antibodies such as immunoglobulins IgA and IgG (Obianwuna et al., 2024). Cinnamon, garlic, ginger, turmeric, green tea, and oregano are among the most widely known herbs for their immune-stimulating properties (Jimoh et al., 2024); (Simoni et al., 2025); (Johnson et al., 2025). The biological effect of phytobiotics largely depends on the chemical composition of the phytobiotics and their specific plant source. These compounds may be administered either as whole plant extracts or in powdered forms, both of which preserve the therapeutic potential of the plant’s active constituents. In poultry production systems, herbs have been shown to have biological impacts, including immune system modulation, which improves the birds’ defensive mechanisms against infections and environmental stresses, and ultimately contributes to enhanced production and egg quality of laying hens (Darmawan et al., 2022). Some phytobiotic plant sources, their main bioactive substances and their immunomodulatory effects in poultry are summarized in Table 1.

Supplementation of Curcuma longa extract has been reported to improve antibody production and immune organ development in broilers and enhance immune response against vaccination (Zhang et al., 2018). Similar effects were observed with the supplementation of sweet orange peel extract, which increased immunoglobulin levels and improved immune responses through anti-inflammatory effects (Pourhossein et al., 2019). Immune cell activity, such as B and T lymphocytes, macrophages, and natural killer (NK) cells, increases at the cellular level when exposed to phytobiotics. These mechanisms are largely mediated by regulating cytokine expression: inhibiting pro-inflammatory cytokines such as IL-1β, IL-6, and TNF-α and increasing anti-inflammatory cytokines such as IL-10, thereby maintaining immune balance (Evrendilek, 2026). This balanced cytokine response prevents excessive inflammation, inhibits tissue damage, and reduces the energy demands of the immune system. Consequently, more nutrients, including energy, are diverted to growth or egg production.

Phytobiotics can reduce chronic inflammation by suppressing these pro-inflammatory pathways and improving immune efficiency. Phytobiotics’ immunomodulatory effects are linked to their impact on inflammatory signaling pathways such as mitogen-activated protein kinase (MAPK) pathways and nuclear factor kappa B (NF-κB), which regulate immune response and cellular stress (Meng et al., 2021). The activation of NF-κB is one of the major mechanisms involved in inflammatory responses and induces pro-inflammatory gene expression. Phytobiotics such as thymol have been reported to inhibit NF-κB activation by preventing phosphorylation and degradation of IκBα, thereby preventing NF-κB translocation into the nucleus (Liu et al., 2022).

The intestinal microflora of poultry is a dynamic and complex microbial community dominated by bacteria from the phyla Firmicutes, Bacteroidetes, Proteobacteria, and Actinobacteria (Clavijo & Flórez, 2018); (Al Hakeem et al., 2023). Dominant microbial phyla, representative genera, and major functions in the poultry intestine are presented in Table 2. Under normal conditions, beneficial bacteria such as Lactobacillus and Faecalibacterium spp. predominate in the small intestine and are important for maintaining microbial balance and inhibiting pathogen colonization via competitive exclusion mechanisms (Naeem & Bourassa, 2025). Furthermore, bacteria such as Bifidobacterium and Enterococcus participate in fermentation and short-chain fatty acids (SCFAs) production, which are important for gut health (Wang et al., 2025). However, disruption of microbial balance may increase the population of pathogenic microbes, thereby highly influencing poultry health and performance.

Phytobiotics, as plant-derived bioactive compounds, are a viable alternative for gut microbiota modulation by inhibiting pathogenic bacteria without impacting beneficial microorganisms and improving intestinal mucosal integrity (Darmawan et al., 2022). They can improve gastrointestinal health and poultry performance through several mechanisms, such as inhibiting the growth of pathogenic bacteria, disrupting microbial cell membranes, and interfering with microbial enzymatic systems (Darmawan et al., 2022); (Rachwał & Gustaw, 2025).

Studies have reported that Moringa oleifera leaves, Carica papaya leaves, Anredera cordifolia leaves, and Centella asiatica leaves possess significant potential as natural phytobiotics (Song et al., 2024); (Rusli et al., 2025); (Akhter et al., 2021). Their bioactive compounds, including polyphenols, flavonoids, saponins, alkaloids, triterpenoids, and papain, are known to inhibit the growth of pathogenic bacteria and improve the health and immune system of poultry. These bioactive compounds inhibit bacteria through complex mechanisms at the cellular and molecular levels. Thymol and carvacrol impact the integrity of bacterial cell membranes through interactions with the phospholipid bilayer, increasing membrane permeability and leading to leakage of ions and other cytoplasmic components (Moghrovyan & Sahakyan, 2024). Flavonoids may affect bacterial gene expression by disrupting DNA/RNA replication and transcription, leading to bacterial death. Moreover, flavonoids inhibit protein synthesis or block the function of some enzymes to kill pathogenic bacteria, thus interfering with the processes of protein synthesis and modification, ultimately resulting in bacterial death (Zhang et al., 2025).

Bioactive compounds also interfere with biofilm formation and quorum sensing systems in pathogenic bacteria, which are key factors in microbial resistance against antibiotics and extreme environmental conditions (Samrot et al., 2021). Flavonoids, eugenol, and carvacrol can disrupt the generation of signaling molecules, thereby reducing virulence gene expression and bacterial colonization of host tissues. Naringin can induce oxidative stress by forming ROS, destroying microbial proteins, lipids, and DNA (Han & Lee, 2022). Additionally, saponins, capsaicin, flavonoids, catechins, and quercetin promote the growth of beneficial bacteria, such as Lactobacillus and Bifidobacterium, thereby enhancing short-chain fatty acid (SCFA) production, especially acetate, propionate, and butyrate. These metabolites serve as an energy source for intestinal epithelial cells and strengthen the integrity of the intestinal barrier, maintain immune homeostasis, and lower intestinal pH, creating an unfavorable environment for pathogenic bacteria (Singh et al., 2025); (Wang et al., 2025).

The relationship between intestinal barrier and intestinal morphology in poultry is important, as both are key factors in the maintenance of gastrointestinal health, nutrient absorption efficiency, and production performance. The intestinal barrier consists of the mucus layer, gut microbiota, intestinal epithelial cells, mucosal immune system, and tight junction proteins, which work together to protect the gastrointestinal tract from pathogenic bacterial infection, toxins, and harmful antigens, and to modulate intestinal permeability (Song et al., 2024); (Proszkowiec-Weglarz et al., 2020). Positive effects of phytobiotics on intestinal morphology in poultry are presented in Table 3. Proper intestinal barrier integrity maintains the structure of the intestinal mucosa and thus allows for optimal digestion and nutrient absorption. Generally, intestinal health in poultry is associated with positive intestinal morphology (optimal villus height, normal crypt depth, and a high villus height-to-crypt depth ratio (VH/CD ratio). Higher villi represent a larger absorptive surface area, leading to increased nutrient absorption capacity, while shallow crypts indicate less tissue damage and more efficient enterocyte regeneration (Belote et al., 2023). Conversely, destruction of the intestinal barrier may result in epithelial damage, villus atrophy, crypt hyperplasia, and damage to tight junction proteins, which can increase intestinal permeability and lead to the translocation of pathogenic bacteria and endotoxins into intestinal tissues. These conditions lead to mucosal inflammation, increased oxidative stress, decreased nutrient absorption efficiency, and ultimately impact growth performance in poultry (Sharma & Kim, 2024). Therefore, intestinal morphological parameters (villus height, villus surface area, crypt depth, and VH/CD ratio) are commonly used as primary indicators to assess intestinal barrier integrity and gastrointestinal physiological status in poultry.

In recent years, phytobiotics have been widely used as natural alternatives to AGPs for the enhancement of intestinal health in poultry. The action of phytobiotics is related to different bioactive compounds of plant origin with antimicrobial, anti-inflammatory, and antioxidant activities, which help maintain intestinal barrier integrity and improve intestinal morphology. Phytobiotics have been shown to inhibit the production of pro-inflammatory cytokines such as IL-6 and TNF-α, which are related to epithelial damage and increased intestinal permeability, thereby suppressing inflammatory responses (Evrendilek, 2026). The reduction of inflammation helps preserve mucosal integrity, maintain villus structure, and minimize enterocyte damage. Furthermore, phytobiotics have a potent antimicrobial effect on pathogenic bacteria and enhances intestinal microbial balance by increasing the number of beneficial bacteria (Darmawan et al., 2022); (Singh et al., 2025). A stable microbiota is important to maintain a healthier intestinal environment and proper epithelial regeneration. Recent studies suggest that allicin and curcumin can upregulate tight junction protein expression such as occludin and claudin, thus enhancing intestinal barrier integrity, decreasing intestinal permeability, and preventing mucosal damage (Gao et al., 2022). Curcumin has been shown to upregulate tight junction protein expression, including occludin and zonula occludens-1 (ZO-1), thereby strengthening the intercellular junctions of epithelial cells and reducing intestinal permeability. Moreover, curcumin prevents oxidative damage to intestinal epithelial cells by inhibiting the NF-κB inflammatory pathway and activating the Nrf2 antioxidant signaling pathway (Xu et al., 2024); (Wu et al., 2022). Nrf2 activation increases the production of endogenous antioxidant enzymes to protect enterocytes from damage due to free radicals. Inhibition of NF-κB suppresses inflammatory responses that may damage the intestinal mucosal tissues (Wu et al., 2022). Collectively, these antioxidant and anti-inflammatory mechanisms preserve epithelial integrity, promote enterocyte regeneration, and maintain villus architecture and height, thus improving intestinal morphology and absorptive function.

The supplementation of phytobiotics has been shown to increase the villus height of the duodenum, jejunum, and ileum and to improve the VH/CD ratio, which is an indication of an improvement in nutrient absorptive capacity and intestinal health in studies on broiler chickens (Galamatis et al., 2025); (Ozturk et al., 2026). Similar improvements in villus height and VH/CD ratio have also been reported in Pekin ducks (Hu et al., 2025), quails (Mahmoud et al., 2025), and laying hens (Xu et al., 2024). Meanwhile, flavonoids, quercetin, and catechins show beneficial effects by enhancing local antioxidant activity, alleviating mucosal inflammation, and modulating the gut microbiota composition, thereby increasing the production of beneficial metabolites such as SCFAs (Singh et al., 2025). SCFAs, especially butyrate, help maintain the integrity of the mucosa and the structure of the villi by tightening the tight junctions (Mathewson et al., 2016). These effects improve intestinal morphology as reflected by increased villus height, decreased crypt depth, and increased VH/CD ratio. This indicates lower mucosal damage and more energy allocated to growth and nutrient absorption instead of tissue repair (Sharma & Kim, 2024). Additionally, flavonoids have been reported to enhance mucus production by stimulating goblet cell activity and enhancing mucin genes such as MUC2 (Damiano et al., 2018). The increased thickness of the mucus layer protects the villus surface from pathogenic invasion and toxins, thus reducing epithelial injury and enhancing the efficiency of nutrient absorption (Proszkowiec-Weglarz et al., 2020).

Numerous studies have reported that plant extracts or powders such as ginger, turmeric, garlic, noni leaves, moringa leaves, and mangosteen peel serve as a source of phytobiotics and result in better poultry performance (Table 4). For instance, the use of 0.6% turmeric powder improved the health status of ducks, indicating an increase in the number of erythrocytes, hematocrit, hemoglobin concentration, and the percentage of total lymphocytes (Nova & Yellita, 2015). Meanwhile, the combined supplementation of 1% mangosteen peel meal and 1% turmeric meal in a duck diet has been proven to be more effective in increasing body weight and reducing mortality compared to single administration (Kusmayadi et al., 2019). The content of curcumin in turmeric and xanthones in mangosteen peel may synergize in improving digestive tract health by balancing the microflora population through their antimicrobial properties. Curcumin and xanthones are also antioxidant compounds that can protect enzymes from free radical damage, increasing their secretion and function in the poultry digestive system (Zhang et al., 2018); (Zhang et al., 2015); (Kusmayadi et al., 2019). Thus, it can maximize digestibility and nutrient absorption to increase body weight. Another study using 2.5% to 10% Moringa oleifera leaf meal in a laying hen diet accelerated follicle number and egg production (Shen et al., 2022). This positive effect is due to the main phenolic content in Moringa oleifera leaves, namely kaempferol, quercetin, myricetin, chlorogenic acid, gallic acid, luteolin, and rutin (Prabakaran et al., 2018); (Yulianto et al., 2024). The antioxidant properties of quercetin and kaempferol in Moringa oleifera leaf can inhibit ROS formation during follicle formation, prevent fatty peroxides, which are precursors of egg yolk formation, and protect egg yolk transport from the liver to the ovaries (Kusmayadi et al., 2019); Prabakaran et al., 2018). Additionally, the addition of a 11 mg/kg body weight fruit leaf (Morinda citrifolia L.) extract enhanced broiler performance, Lactobacillus bacteria, and villous height (Paredes-López et al., 2026). However, (Ismoyowati et al., 2019) reported that supplementation of garlic, turmeric, and ginger (3% each) in the diet of ducks did not affect body weight gain, feed intake, and feed efficiency but yielded a higher percentage of the carcass.

Although phytobiotics have shown potential effects on poultry health and production performance, the processing methods, storage conditions, and handling practices affecting the stability of bioactive compounds have a great influence on their biological efficiency. The common application of plant herbs is by drying and flouring the plant parts with optimal drying temperatures for preserving vitamin C, flavonoids, polyphenols, glycosides, volatile compounds, and antioxidant activity being 50-60 °C, 60-70 °C, 55-60 °C, 45-50 °C, 40-50 °C, and 50-70 °C, respectively (El Gamal et al., 2023). The decrease in total polyphenolic bioactive compounds in dry products can be caused by chemical decomposition due to oxidation during processing and storage, thus decreasing the antioxidant and antimicrobial activities of phytobiotics and reducing their biological effects in poultry. In fact, thermal treatment at the right temperature can result in the rupture of plant cell walls, which further increases the extraction process of phenolic compounds. Heating extracts of plant bioactive compounds at 50 °C increased phenolic compound content and antioxidant activity but decreased vitamin C content due to its thermolabile nature, which is easily oxidized by heating (Cunha et al., 2021). Meanwhile, (Sharmin et al., 2016) reported that extraction at temperatures above 40 °C for more than 40 minutes degraded polyphenolic compounds and flavonoids, thereby reducing their yield. Therefore, optimizing extraction temperature and processing time is an important step in herbal technology, as it aims to maximize the recovery of phytochemicals while minimizing thermal degradation. Storage for 50 days has a significant effect on decreasing bioactive compound yield and antioxidant activity (Tobal & Rodrigues, 2019). The decrease in anthocyanins, one of the flavonoid compounds, also fell to 44% after 21 days of storage at 30 °C (Alves et al., 2017). (Tummanichanont et al., 2018) also found that the total phenolic content of dried Andrographis paniculata leaves stored at 25 and 35 °C for 6 months decreased by 50.92% and 56.32%, respectively. Similarly, DPPH values decreased by 19.96% and 23.77%, respectively. Therefore, suitable drying and storage conditions, including temperature control, protection from light and oxygen, and airtight packaging, are important for minimizing the degradation of bioactive compounds. In addition, encapsulation is another effective approach to protect highly sensitive bioactive compounds from degradation and to enhance their stability during storage.

Additionally, the processing and storage stability and the practical efficacy of phytobiotics in chicken production are also closely associated with the implementation of proper farm biosecurity procedures. Good biosecurity management promotes poultry health, reduces pathogen exposure, and enhances the efficacy of phytobiotics in maintaining poultry performance and reducing disease cases. The strict application of biosecurity correlates negatively with bacterial resistance in animals, enhances animal health, and decreases the need for antimicrobial use (Raasch et al., 2018). According to Pinto et al. (Pinto et al., 2020), good biosecurity includes bio-containment, bio-exclusion, and bio-management. Bio-containment prevents the spread of pathogenic bacteria or diseases to other farms through cleaning and disinfecting the farm. Bio-exclusion prevents exposure to new pathogens by requiring showering and monitoring health status before entering the farm, controlling vehicles, and restricting the movement of people and animals within the farm. Meanwhile, bio-management controls and manages pathogens that already exist on the farm, such as using all-in-all-out systems.