In recent years, the significance of intestinal microbiota in poultry nutrition, health, physiology, and immunity has emerged (24). The commensal microbiota, affixed to the intestinal epithelium, is crucial for preserving homeostasis and preventing pathogen colonization (25). In order to guarantee that commensal microorganisms are tolerated, pathogens are identified and controlled, and potentially harmful commensal microorganisms like Clostridium perfringens and Escherichia coli are kept in check, the microbiota works in tandem with the chicken immune system, aiding in the immune cells’ maturation and training (26). Additionally, it increases the epithelium absorptive surface by producing metabolites, including SCFAs, indoles, vitamins, and antimicrobial compounds, which aid in the formation of the lamina propria, mucus layer, and epithelial monolayer (27).

The gut microbiota is the first line of defence against infections and significantly affects chickens’ nutritional, physiological, and health conditions (28). The gut microbiota has been divided into pathogenic (E. coli, Campylobacter, and Salmonella) and beneficial (Lactobacilli and Bifidobacteria) bacteria based on their effects on the host (29). Competition for resources, the generation of harmful substances (such as volatile fatty acids and low pH), competition for binding sites on the gut epithelium, and immune system stimulation are some of the ways that the gut microbiota inhibits pathogens (169).

Poultry’s early gut health, gut microbiota, nutritional status, and immunological status have been reported to greatly impact their growth and development (30, 31). Dietary components can affect health and growth performance during post-hatch life by altering the gut microbiota and the intestinal production of metabolites (32). According to Bindari and Gerber (27), the gut-health interaction is the symbiotic equilibrium between the intestinal tract and the microbiota, which means that animal welfare and health are unaffected and are regarded as significant determinants. The immune system and general health are also impacted by the gut flora (33). Human antibiotic resistance and infection can also be determined by the microbiota of the chicken digestive tract (34). The digestive tract indicates the habitat of the microbiota that influences chickens’ digestive systems. Essential biological processes like human physiological ageing, dairy cow methane emission, pig nutrition digestion, absorption and metabolism, and chicken health and productivity are all significantly influenced by the gut microbiota (35, 36).

A key factor in regulating the activation and control of the immune system in broiler chickens is the microbiota in the digestive tract, which varies depending on the feed, location, and age of the bird (37). In the early stages of their development, newly hatched chicks depend on innate immune responses. Microbial administration is one method to increase and stimulate the immunological development of chickens both before and after hatching (38).

There are several ways in which the microbiota’s function in the host’s physiological, nutritional, developmental and immunological processes benefits the gut health, productivity, and general wellbeing of chickens (37). In addition to helping with digestion and nutrient absorption, the gut microbiota also supports the development and operation of the host immune system, the intestinal epithelial barrier, and the competition with pathogenic microorganisms to stop their detrimental spread (39). Intestinal health is largely determined by the symbiotic connection between the host and gut microbiota under normal circumstances. However, “dysbiosis,” or an unbalanced host-microbe connection, can result from a disruption in the gut microbiota (40).

Poultry welfare and gut health are closely related since poor gut health can result in lower feed intake, growth performance issues, and digestive diseases. The severity of intestinal damage linked to coccidiosis, necrotis enteritis, and general intestinal inflammatory and disease disorders including dysbiosis has been assessed using gut health score systems (15, 27).

The term “dysbiosis” describes an imbalance or disturbance in the gut microbiota in which harmful bacteria multiply and helpful microbes decline. Poor nutrition, stress, antibiotics, and other environmental variables can all lead to dysbiosis. Dysbiosis in chickens can have a number of detrimental effects. By harming the intestinal lining and decreasing the availability of enzymes that aid in food digestion, dysbiosis might hinder the gut’s capacity to absorb vital nutrients (41). This results in lower feed conversion efficiency (FCR) and subpar growth performance.

Dysbiosis can also result from factors that upset the balance of the gut microbiota, such as transportation, changes in the environment, or crowding. The gut’s capacity to maintain a healthy barrier function may be compromised by this imbalance, raising the possibility of inflammatory reactions and pathogen invasion. Additionally, gut motility and feed conversion efficiency can be impacted by chronic stress (42). The gut’s immune system is weakened by dysbiosis, which also lowers the generation of antimicrobial peptides. This increases the risk of gastrointestinal diseases such as coccidiosis and necrotic enteritis.

A number of risk-reduction techniques have been investigated in light of the dangers posed by gastrointestinal disorders, dysbiosis, and antibiotic resistance; one such strategy is using feed additives.

Understanding the microbial communities in the gut is important for creating safe feed additives and modifying diets to improve gut health and performance (15). Feed additives are natural, non-nutritive ingredients added to the basic diet in small amounts to enhance the quality of feed and animal-based foods and the health and performance of animals. They enhance animal development, intake, absorption, and nutritional assimilation by influencing physiological processes like stress resistance and immunological function (19, 43).

Poultry nutritionists became interested in natural feed additives replacing AGP products (3, 44, 45). Among the many natural feed additives for chicken feed, phytogenic feed additives (PFAs) are highly recommended and accepted by consumers (46–49).

PFAs are naturally occurring, are diverse groupings that are less harmful, leave no residue, and are perfect non-antibiotic growth promoters. They are made from plants, herbs, fruit, spices, and their essential oil, and they are utilized as feed additives in the production of meat animals (43, 45). PFAs are a diverse class of bioactive plant-derived compounds or plant-based products high in phenolics and flavonoids added to animal meals to increase productivity (20, 50). Phytogenic compounds are a wide range of active ingredients that can be obtained from different types of plants. Categories of phytogenic compounds include oleoresins, spices, botanicals, herbs, and essential oils.

Phytogenics contribute to better gut health through their capacity to enhance the gut microbiota, facilitate digestion, and increase immunity. They can have a favorable impact on the gut microbiota by encouraging the growth of beneficial bacteria and preventing the formation of pathogenic microbes. A more diversified and balanced microbiota results from this, which is crucial for preserving gut health and averting gastrointestinal disorders (51). Through the stimulation of digestive enzyme release, increased nutrient absorption, and enhanced enzyme activity, phytogenics can increase the efficiency of poultry digestion. Growth, feed consumption, and general productivity all improve as a result. The digestion of carbs, lipids, and proteins is facilitated by digestive enzymes, including amylase, lipase, and protease, which are secreted in response to phytogenic stimulation. This aids in the more effective digestion and absorption of nutrients by poultry, especially in young birds or stressed birds (52).

Through tight junction protein enhancement and intestinal epithelial integrity promotion, phytogenics can fortify the gut barrier and avert leaky gut syndrome. A stronger gut barrier lowers the risk of systemic infections and enhances general health by preventing toxic substances and dangerous microorganisms from entering the bloodstream. Liu et al. (29).

Given their beneficial impacts on animal health, phytogenics are becoming increasingly popular as affordable feed additives. PFAs can be added to the diet in dry form or as extracts, and the makeup of the bioactive biomolecules in them differs based on the plant components utilized, such as seeds, leaves, wood, or bark (53).

Phytogenic feed additives (PFAs) exert their beneficial impacts on the gastrointestinal tract via various physiological mechanisms. They improve nutrient absorption and digestion by inducing the release of digestive enzymes. They increase feed efficiency (FE) by modifying the expression of hypothalamic neuropeptides linked to feeding behavior. Peripheral intermediate metabolisms, such as lipid metabolism and signaling pathways associated with protein synthesis, also regulate FE and are influenced by PFA bioactivities (43). PFAs enhance feed palatability, digestibility, and nutrient absorption. They also modulate the structure of the animal’s intestinal microbiome and enhance performance by promoting the biological activity of plant secondary compounds with antioxidative features. Additionally, PFAs inhibit the growth of pathogenic microorganisms in poultry (18). Certain phytogenics also strengthen gut morphology, boost immunological responses, and lessen the effects of environmental stressors, thereby contributing to improved poultry health and growth performance (19, 20, 62, 63). They have been shown to enhance gut health by decreasing pathogenic bacterial colonies, reducing fermentation by-products like ammonia and biogenic amines, lowering gut-associated lymphatic tissue activity, and improving the digestion of pre-caecal nutrients (43).

Phytogenics influence poultry gut health via some interrelated cellular, microbial, and molecular processes. Its antibacterial activity is one of its main modes of action. According to Yang et al. (18) and Yammine (68), compounds including thymol, carvacrol, and cinnamaldehyde reduce the growth of harmful bacteria like Clostridium perfringens and Escherichia coli by disrupting bacterial cell membranes, changing membrane permeability, and inhibiting quorum sensing. By specifically encouraging beneficial bacterial populations like Lactobacillus and Bifidobacterium, phytogenics not only have antibacterial qualities but also help to modulate the gut microbiota, supporting microbial balance and enhancing gut resilience (69, 70).

Because phytogenics contain secondary metabolites from plants, such as flavonoids and phenolic acids, they also have strong antioxidant properties. These substances protect the integrity of tight junctions and reduce inflammation by scavenging free radicals and reducing oxidative stress in intestinal epithelial cells (19, 20). Another crucial mechanism is immune modulation, whereby specific phytogenics enhance mucosal immunity and control the activity of gut-associated lymphoid tissue by activating innate immune responses via Toll-like receptor signaling and modifying the production of cytokines, such as interleukins and interferons (23, 71).

By promoting mucin production and upregulating the expression of tight junction proteins like occludin and claudin-1, phytogenics also improve intestinal barrier function by lowering intestinal permeability and preventing pathogen invasion (72, 73). Additionally, they encourage the release of digestive enzymes such as amylase and protease, which enhance the gut’s ability to absorb and digest food (23, 74). When taken as a whole, these processes highlight the diverse ways phytogenics support and enhance poultry intestinal health.

Tables 1–4 categorize phytogenic compounds based on their primary bioactive components and physiological effects on poultry gut health. Table 1 highlights essential oil–based herbs such as oregano, cinnamon, thyme, and rosemary. Their active constituents, such as thymol, carvacrol, cinnamaldehyde, and linalool exert antimicrobial effects, stimulate beneficial gut microbiota (e.g., Lactobacillus, Bifidobacterium), and improve intestinal morphology by increasing villus height and enzyme secretion. These phytogenics are widely recognized for enhancing digestive efficiency and protecting gut health and integrity. The herbal extracts with anti-inflammatory or antioxidant properties, such as turmeric, black cumin, and bitter leaves, are shown in Table 2. Rich in bioactives like curcumin, thymoquinone, and flavonoids, these herbs reduce intestinal inflammation and oxidative stress, support mucosal healing, and enhance intestinal morphology. Their protective roles make them particularly valuable in poultry that is stressed or exposed to pathogens. Plants such as chicory and moringa are presented in Table 3 due to their high content of fermentable fibres and polyphenols. These compounds act as prebiotics, enhancing the growth of beneficial gut microbes and improving intestinal architecture. Their inclusion in diets has been linked to enhanced villus development and the inhibition of enteric pathogens, such as E. coli and Salmonella. This diverse group (Table 4) includes sweet wormwood, garlic, and ginger. These herbs enhance gut health through mechanisms such as boosting digestive enzyme secretion, improving motility, and strengthening the gut barrier. Their bioactive compounds (e.g., artemisinin, allicin, gingerol) also exhibit antimicrobial activity and aid in nutrient absorption.

Although the potential benefits of phytogenic feed additives, ranging from enhanced gut health and immunity to improved growth performance, are well documented. However, their widespread adoption remains limited due to several practical and scientific challenges. A significant constraint is the variability in the composition and effectiveness of phytogenic products. These inconsistencies stem from biological factors such as plant species, cultivation location, harvest timing, and processing techniques like extraction or distillation. Additionally, storage conditions (light, temperature, oxygen exposure, and duration) can influence the stability and bioactivity of phytogenic compounds (67, 134, 135). This variability undermines confidence among producers and complicates the standardization of phytogenic products (19–21).

Furthermore, phytochemicals exhibit dose-dependent effects, with research indicating that more pronounced benefits are observed when administered during early life stages in poultry (136). However, suboptimal or inconsistent dosing can lead to ineffective outcomes (137). Some phytogenic substances may also produce undesirable effects such as off-flavors, toxicity, or interactions with other feed ingredients (138, 139). The volatility of certain compounds further contributes to inconsistent concentrations in final products (18). Economic factors also present barriers. The relatively high cost of many commercial phytogenic additives, coupled with limited field-scale trials that validate their benefits in commercial settings, makes their adoption less attractive, especially in low-and middle-income countries (109). Moreover, a general lack of technical knowledge among farmers and feed manufacturers hinders proper application and potential impact.

Despite these limitations, several emerging trends and innovations offer promise for the broader adoption of phytogenic products. The global shift toward antibiotic-free (ABF) poultry production creates a conducive environment for the use of natural additives. Phytogenics, with their demonstrated roles in pathogen control, immune modulation, and gut health, are well suited for ABF systems (62, 63, 140, 141). Advances in formulation technology, such as microencapsulation and standardized extraction techniques, are enhancing product consistency and bioavailability (21, 142). Additionally, the increased availability of cost–benefit analyses linking phytogenic use to improved feed conversion, growth, and health outcomes will strengthen their economic justification. Supportive regulatory frameworks, along with livestock farmer training, extension services, and on-farm demonstrations, will also play an important role in integrating phytogenics into mainstream poultry nutrition.

The application of phytogenic feed additives in poultry production is a promising alternative to antibiotic growth promoters, yet several critical knowledge gaps hinder their optimal use. Future research should first focus on standardizing phytogenic formulations, particularly through quantitative profiling and identification of bioactive constituents using advanced analytical tools, such as LC–MS/MS and NMR spectroscopy. This will help to reduce variability in efficacy across batches and production systems. Secondly, precise dose–response studies are needed to establish minimum effective concentrations, identify potential toxicity thresholds, and evaluate their interactions with feed matrices under commercial pelleting and extrusion processes. Research into the stability of compounds during storage and feed manufacturing is also required to enhance product shelf life and ensure consistent performance.

Another priority is the investigation of synergistic or antagonistic interactions between phytogenics and other functional feed additives (like probiotics, prebiotics, enzymes, and organic acids). For example, studies should explore whether combinations enhance gut barrier integrity or modulate immune responses more effectively than when used alone, using factorial design experiments and host-microbiome readouts. The development and testing of advanced delivery technologies, such as microencapsulation, nanoemulsions, and pH-sensitive coatings, can enhance the stability, bioavailability, and site-specific release of phytogenic compounds in the gastrointestinal tract. These technologies should be evaluated through controlled-release assays and gut transit studies using markers or imaging. To unravel the precise mechanisms of action, integrating multi-omics platforms (such as transcriptomics, proteomics, metabolomics, and microbiomics) is crucial. These approaches can provide insights into host-gut microbiota interactions, immune modulation, and metabolic shifts induced by specific phytogenic compounds or their combinations. Moreover, longitudinal in vivo trials across diverse poultry genotypes, production systems (such as intensive versus free-range), and environmental conditions are necessary to assess the robustness, reproducibility, and long-term effects of phytogenic supplementation on productivity, welfare, and product quality.

Furthermore, the establishment of regulatory frameworks, safety thresholds, and validated quality control protocols is vital for the large-scale commercialization of phytogenics. Such frameworks should be based on sound scientific data and harmonized across regions to ensure the safe, sustainable, and economically viable integration of phytogenics into poultry nutrition programs, particularly in the context of antibiotic-free production and climate-resilient livestock systems.