The promise of pectic oligosaccharides as a novel sustainable additive in poultry production: A systematic review

Abstract

The prohibition of antibiotic growth promoters in animal feeds due to their well-known hazards has driven the accelerated research and development of novel practicable alternatives, among which functional oligosaccharides are characterized as one of the most promising candidates because of their stability, safety and excellent biological activities. Pectic oligosaccharides (POS) are an emerging class of functional oligosaccharides obtained through physicochemical or biological degradation (especially the enzymolysis) of pectins (a crucial kind of plant cell wall components). The preparation of POS is economically feasible, which not only overcomes the anti-nutritional impacts of native pectins in plant ingredients, but also obtains other benefits for poultry, because the prepared POS possess numerous functions, such as optimizing gut microbiome via both prebiotic and non-prebiotic actions, regulating lipid metabolism and immune responses, as well as exerting antioxidant and antitumor properties. Noticeably, the above functions of POS that depend largely on their structure have been primarily validated in laboratory animals or in vitro models, while the related researches in poultry or other farm animals are relatively few. The present review systematically discusses the preparation methods of POS, their biological activities and underlying mechanisms that may benefit poultry growth and health, as well as their structure-activity relationships. We also summarize the currently limited evidences on the positive roles (such as improvements of production performance along with intestinal and genital health) of POS in poultry nutrition, thus supporting the promise of POS as a novel sustainable additive in poultry diets. Since the application of POS in feeds is still underexplored, future studies deserve to be conducted to elucidate the definite mechanisms together with the structure-effect and dose-effect relationships of POS, as well as the synergy between POS and other additives (e.g. probiotics) in poultry nutrition. Such research efforts are anticipated to further extend the role of POS as a cost-efficient and sustainable additive in advancing poultry production.

Introduction

Antibiotics were broadly used in animal production to promote growth performance and prevent bacterial-related disorders for the past few decades. However, the abuse or long-term usage of antibiotics has caused a series of side effects such as increases in bacterial antibiotic resistance and antibiotic residues in animal products coupled with emergence of environmental pollution, thus seriously threatening sustainable animal production and public health. Against this background, plenty of countries and regions worldwide have restricted or prohibited the use of antibiotics in feeds. Thereby, there is an increasing demand for exploiting practicable feed additives as antibiotic substitutes in animal production. Among them, functional oligosaccharides have garnered much attention due to their safety, stability, and multiple biological functions.

Pectic oligosaccharides (POS) are viewed as an emerging class of functional oligosaccharides derived from degradation of pectins through physical, chemical or biological methods especially the enzymolysis approach. Pectins are a type of acidic heteropolysaccharides widely present in the cell walls of plant feeds, and represent one of the main components of by-products from the processing of agricultural crops (e.g. citrus, apples, and sugar beets) (de Alencar et al., 2025). Consequently, the raw materials for POS preparation are abundant and cost-effective, but the molecular structure of POS may vary depending on the sources of raw materials and manufacturing methods (Singh et al., 2020; Thikham et al., 2023). POS exhibit high water solubility and stable physicochemical properties, which can withstand high temperatures during feed pelleting and remain undegradable under the actions of digestive enzymes secreted by the gastrointestine itself (Thikham et al., 2023). However, POS can be selectively fermented by specific beneficial bacteria in the intestine, which allows them to function as an emerging prebiotic similar to other classical functional oligosaccharides, thereby improving the composition of gut microbiota and their metabolites such as short-chain fatty acids (SCFA) (Singh et al., 2020; Thikham et al., 2023; Wilkowska et al., 2025). With the deepening of research, it has been discovered that POS are capable of exerting other biological functions beyond the prebiotic effect, such as bacteriostasis (Long et al., 2022; Gao et al., 2023), lipid metabolism regulation (Hu et al., 2021), immunomodulation (Singh et al., 2020; Yeung et al., 2021), antioxidant property (Yeung et al., 2021; Amini-Rourani et al., 2025; Wilkowska et al., 2025), and antitumor action (Rajulapati et al., 2021; Amini-Rourani et al., 2025). Remarkably, the efficacy of the above actions of POS is closely related to their structure, such as the molecular weight (MW) or degree of polymerization (DP) (Long et al., 2022; de Alencar et al., 2025), along with the type of side-chain groups and degree of esterification (Singh et al., 2020; Pattarapisitporn et al., 2024; Zwolschen et al., 2024). Given the aforementioned multiple biological functions, POS application is deduced to positively impact animal production, despite that most of the previous researches regarding POS were implemented using laboratory animals or in vitro models. In fact, the currently limited investigations have revealed the benefits of POS in farm animal production. For instance, dietary POS supplementation was reported to fortify immune responses and antioxidant capacity of Rotavirus-infected piglets, thereby protecting their intestinal barrier and growth performance as well as lowering their diarrhea incidence (Chen et al., 2017; Mao et al., 2017b; Mao et al., 2019). It was also found to result in improvements in carcass traits and meat quality, such as increase in loin eye area, decreases in cooking loss and drip loss concurrent with increase in intramuscular fat content of the longissimus dorsi muscle in finishing pigs (Mao et al., 2017a). In poultry, supplemental POS was indicated to promote reproductive performance in broiler breeders potentially by enhancing antioxidant capacity along with intestinal and ovary health (Zhao et al., 2019; Mao et al., 2021; Wang et al., 2021b). Moreover, our previous study disclosed ameliorations in growth performance, organ indexes, and intestinal antioxidant capacity in aflatoxin B₁-exposed broiler chicks in response to POS supplementation (Ye et al., 2025), which also alleviated lipopolysaccharide (LPS)-caused intestinal inflammatory damages and poor growth performance in broiler chicks (Ling et al., 2026). Nevertheless, the application value of POS in animal production has not yet received sufficient attention. Consequently, the present review article concentrates on discussing the preparation methods, biological activities, and structure-activity relationships of POS, as well as summarizing their application effects in poultry production, thus providing comprehensive evidences for highlighting the promise of POS as a novel sustainable additive in poultry diets. This review also looks ahead to the future research trends and the development strategies for better sustaining the integration of POS into poultry production.

Generalization of pectins

Pectins are the complex heteropolysaccharide found in the cell walls of multifarious plants especially agricultural by-products such as fruit wastes and oil-seed meals. In general, pectins can be categorized into protopectin and soluble pectin, the former of which is highly methylesterified and water-insoluble, serving as the initial form of natural pectins in plant cell walls. During the maturation of plant tissues, protopectin is converted into soluble pectin under the action of protopectinase. Based on the distribution of side chains, the structure of pectins can be classified into four distinct structural domains: homogalacturonan (HG), xylogalacturonan (XG), rhamnogalacturonan (RG)-I, and RG-II (de Alencar et al., 2025). HG is the simplest and most abundant structural domain of pectin molecules, consisting of a linear chain of α-1,4-linked D-galacturonic acid (D-GalA) residues. The carboxyl group at the C6 position of D-GalA residues can undergo varying degrees of methyl esterification, and the hydroxyl group at C2 or C3 position may be acetylated (de Alencar et al., 2025). The backbone of XG is also composed of D-GalA connected through α-1,4-glycosidic bonds, with β-D-xylose side chains attached to the O-3 position of the D-GalA residues in the backbone. RG-I has a backbone composed of alternating L-rhamnose and D-GalA units, and the C-4 position of rhamnose residues is often substituted with certain side chains such as galactans and arabinans. RG-II is the least abundant but most structurally complex domain, whose backbone is composed by D-GalA units polymerized via α-1,4-glycosidic bonds and linked with various side chains formed by structurally complex oligosaccharides (de Alencar et al., 2025). Although pectins may exert some beneficial physiological functions (de Alencar et al., 2025), they represent a typical non-starch polysaccharide and act as an anti-nutritional factor for animals due to the high molecular weight and viscosity. It has been proved that dietary pectins can elevate intestinal chyme viscosity, reduce digestive enzyme activities, hinder the sufficient contact between digestive enzymes and chyme, as well as increase endogenous amino acid losses, subsequently compromising nutrient digestion and utilization of animals (Pluschke et al., 2018; Adedokun et al., 2020). Given these anti-nutritional effects of pectins, addition of pectinase to plant-based animal diets is often considered to degrade the contained pectins (Azzaz et al., 2021; Niu et al., 2022b; Niu et al., 2023). One of the main degradation products of pectins is represented by POS.

Definition and structure of POS

In the field of biochemistry, oligosaccharides are generally defined as oligomers formed by the polymerization of 2 to 10 monosaccharides (namely DP 2∼10) via glycosidic bonds. This definition is based merely on the molecular structure of oligosaccharides. With the advancement of research, it has been discovered that some oligosaccharides with DP greater than 10 have similar or even better efficacy compared to the same type of oligosaccharides with DP less than 10 (Li et al., 2016; Wilkowska et al., 2025). Accordingly, the current definition of oligosaccharides has been broadened beyond the previous DP limit of 2∼10. Regarding POS, their DP typically falls within the range of 2∼20 (Wang et al., 2022a) or even higher (Di et al., 2017; Wilkowska et al., 2025). In a narrow sense, POS specifically refer to the oligogalacturonic acid, which is originated from the degradation of HG (the dominant structural domain of pectins) and typically composed of a linear backbone polymerized from D-GalA units via α-1,4 glycosidic bonds (as illustrated in Fig. 1). In a broad sense, POS include a class of oligosaccharides obtained by the degradation of all structural domains of pectins. Because pectin molecules consist of various structural domains with complicated group composition, the types of POS in the broad sense are diverse and their structure may differ depending on the raw material sources and preparation methods, thus allowing the variations in the physiological functions and application properties of POS products (Thikham et al., 2023; Pattarapisitporn et al., 2024).

Fig. 1.

The structure of oligogalacturonic acid (a narrow-sense pectic oligosaccharide) with degree of polymerization of 2 to 20. This Fig. was created with the help of ChemDraw software.

Preparation of POS

POS are often prepared by subjecting natural pectins or HG-type pectin (a degradation product of natural pectins) to physical, chemical or biological degradation with a subsequent purification. Physical degradation methods involve the usage of techniques such as ultrasound, microwave, radiation, and high-pressure treatment to break glycosidic bonds in pectin molecules (de Alencar et al., 2025). Chemical degradation refers to using strong acids or oxidizing agents to cleave the glycosidic bonds within pectin molecules (de Alencar et al., 2025). Biological degradation primarily employs pectinase to catalyze the hydrolysis of glycosidic and other chemical bonds within pectin molecules. This method has been more widely utilized due to its environmental friendliness, high efficiency, and specificity (de Alencar et al., 2025). Strikingly, pectinase refers to a general term for all enzymes capable of hydrolyzing pectin molecules and is mainly produced by microorganisms such as Bacillus spp., Aspergillus spp., and Saccharomyces spp. (Azzaz et al., 2021; Zhao et al., 2025).

According to the substrate specificity and action mode, pectinase is usually divided into four major categories: protopectinase, pectin lyase, pectin esterase and polygalacturonase (Thikham et al., 2023; Zhao et al., 2025). Protopectinase mainly cleaves the chemical bonds between pectins and other components (e.g. cellulose and hemicellulose) in plant cell walls, thereby dissolving the insoluble protopectin from the cell wall and converting it into soluble pectins (Thikham et al., 2023). Pectin lyase cleaves the α-1,4-glycosidic bonds in the backbone of pectins or de-esterified pectins (e.g. pectic acid) via β-elimination reactions (Zhao et al., 2025). Pectin esterase does not directly break the backbone of pectin molecules, but mainly catalyzes the hydrolysis of methoxy group on D-GalA residues within the HG domain, generating low-ester pectins or even nonesterified pectins such as polygalacturonic acid (i.e. pectic acid) (Zhao et al., 2025). Polygalacturonase is divided into exo- and endo-types, the latter of which can randomly break the internal α-1,4-GalA-glycosidic bonds in low-ester pectins or pectic acid, thereby generating oligogalacturonic acid (the narrow-sense POS). By referring to the above enzymolysis principle combined with ultrafiltration and ethanol fractional precipitation methods, our research team has prepared POS products (> 90 % purity) with a weight average DP ranging from 2∼20 (Ling et al., 2026; Ye et al., 2025). The general procedures of POS mini-preparation using the enzymolysis approach are summarized in Fig. 2.

Fig. 2.

Summarization of the mini-preparation procedures of pectic oligosaccharides (POS) using the enzymolysis approach. Multi-enzymes, combination of rhamnogalacturonase, arabinoxylanase, and galactanase; HG, homogalacturonan; DP, degree of polymerization; GPC, gel permeation chromatography; MW, molecular weight; FTIR, fourier transform infrared spectroscopy. The materials in this Fig. derive from the BioGDP platform (https://biogdp.com/diagram?id=481232). Natural pectins are first hydrolyzed by multi-enzymes comprising rhamnogalacturonase, arabinoxylanase, and galactanase. The resulting hydrolysate undergoes ultrafiltration to obtain a HG-enriched fraction, which is subsequently deesterified by pectinesterase. The reaction mixture is precipitated using ethanol solution and freeze-dried using freeze dryer to obtain pectic acid (namely polygalacturonic acid), which is then cleaved by polygalacturonase. Following termination of reaction by boiling, the reaction mixture is centrifuged for collection of the hydrolysate in the supernatant. Thereafter, the hydrolysate is precipitated with 35 % ethanol solution and then centrifuged, the collected supernatant is precipitated with 70 % ethanol solution and then centrifuged. The resulting precipitate and supernatant are separately collected. The collected precipitate is freeze-dried and ground to produce the high degree of polymerization (DP) of POS, while the collected supernatant is concentrated via rotary evaporation and then freeze-dried to produce the low DP of POS. Finally, the high-DP and low-DP POS are characterized through GPC analysis of MW distribution and FTIR detection of chemical structure.

Biological activities and action mechanisms of POS

Optimization of gut microbiome

Gut microbiota have been established to influence the growth performance as well as intestinal and systemic health of animals (Kayal et al., 2025; Tardiolo et al., 2025). POS are able to shape gut microbiota and their metabolite composition of animals by elevating the number of beneficial bacteria and reducing the number of harmful bacteria in the intestine (Sori et al., 2022; Wang et al., 2022b; Yu et al., 2023), which may in turn improve growth and health of poultry (Kayal et al., 2025; Tardiolo et al., 2025). The optimization of gut microbiome by POS can be attributed to both prebiotic and non-prebiotic actions of them.

Prebiotic action

POS can be degraded by specific enzymes secreted by certain beneficial gut bacteria (Chung et al., 2017) instead of digestive enzymes secreted by the gastrointestine (Thikham et al., 2023), thus selectively promoting the growth of these beneficial bacteria and conferring them with a competitive advantage over harmful bacteria in the intestine (Thikham et al., 2023; de Alencar et al., 2025). POS also support the growth of beneficial gut bacteria through cross-feeding mechanism (Zwolschen et al., 2024). For example, lactic acid bacteria in the intestine ferment POS to produce lactate, which acts as a key intermediate substrate to drive the growth of other beneficial bacteria and the generation of beneficial metabolites such as SCFA (Chung et al., 2017; Zwolschen et al., 2024). Growing evidences have revealed the role of POS in boosting the proliferation of plentiful probiotic species (e.g. Bifidobacterium longum, Lactobacillus salivarius, and Pediococcus acidilactici) along with the production of lactate, acetate, and propionate (Thikham et al., 2023; Del Amo-Mateos et al., 2024; Pattarapisitporn et al., 2024), as well as stimulating the proliferation of butyrate-producing probiotics including Bacteroides thetaiotaomicron, Faecalibacterium prausnitzii, and Eubacterium eligens (Chung et al., 2017; Pattarapisitporn et al., 2024). In an in vitro fermentation experiment using human colonic microbiota, POS showed a capacity to increase the abundances of beneficial bacteria (such as Lactococcus and Clostridium butyricum) and butyrate production (Zwolschen et al., 2024). In another in vitro fermentation trial using human fecal microbiota, POS exhibited an advantage over galacto-oligosaccharide in elevating the abundances of multiple beneficial bacteria (e.g. Lactobacillus, Bifidobacterium, Bacteroides, Eubacterium, Roseburia, Faecalibacterium, and Prevotella) and the production of SCFA (particularly propionate), as well as in decreasing the abundances of harmful bacteria (such as Vibrio, Escherichia coli, and Bacteroides fragilis) (Bhaiyya et al., 2026). In an in vitro fermentation experiment with porcine fecal microbiota, POS were detected to be more efficient than other functional oligosaccharides (such as isomaltooligosaccharide, xylooligosaccharide, and cellobiose) to increase the abundance of Bacteroides (Tran et al., 2016). In this study, POS also displayed a superiority over xylooligosaccharide in increasing the content of total SCFA, together with a superiority over isomaltooligosaccharide and cellobiose in increasing acetate content (Tran et al., 2016). Similarly, another in vitro fermentation trial with porcine fecal microbiota revealed that POS elevated the contents of acetate, propionate and total SCFA while reducing lactate content, as compared to fructooligosaccharide (Leijdekkers et al., 2014). In in vivo studies, the prebiotic action of POS has also been confirmed. For example, incorporating POS to piglet diet was showed to increase the numbers of Lactobacillus, Bifidobacterium and total bacteria coupled with the contents of acetate and total SCFA in cecal digesta, while reducing Escherichia coli number in cecal digesta (Mao et al., 2017b). Similar findings were described in another study where POS addition tended to elevate total bacterial number and increased the contents of acetate, propionate, butyrate and total SCFA in colonic digesta of finishing pigs (Mao et al., 2017a).

Increased beneficial bacteria induced by POS occupy more adhesion sites on intestinal epithelial cells (IECs), forming a microbial barrier to competitively exclude the growth and colonization of intestinal harmful bacteria (Pahumunto et al., 2023). Besides, SCFA produced from POS fermentation by beneficial bacteria can inhibit intestinal harmful bacteria via both indirect and direct ways. On one hand, SCFA lower intestinal pH and create an acidic extracellular microenvironment, restraining the growth, motility, adhesion, invasion and virulence gene expression of harmful bacteria (Zhang et al., 2020; Ling et al., 2025). On the other hand, SCFA molecules can intactly entry into bacterial cells due to their partial dissociation and membrane penetration properties, which disturb intracellular H⁺ homeostasis of harmful bacteria (e.g. avain pathogenic E. coli), ultimately repressing their growth along with their expression of virulence genes related to adhesion, quorum sensing, two-component system, environmental sustainability and survival (Ling et al., 2025).

Direct antibacterial action

POS can directly inhibit harmful gut bacteria besides through their prebiotic action. Due to the unique physical properties, POS cause shrinkage or even rupture of bacterial cell membrane, which leads to a disruption of bacterial cell membrane integrity with a subsequent leakage of intracellular contents such as nucleic acids, thereby exerting antibacterial effects (Long et al., 2022; Gao et al., 2023). Moreover, POS react with hydroxyl radicals to generate carbon dioxide anion radicals, which can specifically damage bacterial proteins and then contribute to their antibacterial action (Martinov et al., 2017). Gao et al. (2023) reported that the minimum inhibitory concentration (MIC) of POS against E. coli and Staphylococcus aureus was 25 and 50 mg/mL, respectively. Li et al. (2016) reported that POS of different molecular weights exhibited MIC against the above two bacteria ranging from 25∼50 mg/mL and 12.5∼25 mg/mL, respectively. These findings suggest that the antibacterial effect of POS ia not particularly strong, which are contrasted to some other studies. For example, Long et al. (2022) found that the MIC of POS against E. coli, Salmonella typhimurium, and S. aureus was only 0.8, 0.8 and 0.6 mg/mL, respectively, with the inhibition zones of POS at a concentration of 2 mg/mL against these three bacteria being 16.8, 21.4, and 20.1 mm, respectively. Xue et al. (2021) detected that the MIC of POS against the above three bacteria was 0.8, 1.0, and 0.6 mg/mL, respectively, with the respective inhibition zone of 2 mg/mL POS being 18.2, 18.0, and 21.1 mm. In the study of Wang et al. (2022c), even low concentrations (0.2∼1 mg/mL) of POS obviously repressed the growth of E. coli, S. typhimurium, S. aureus and Micrococcus luteus in a dose-dependent manner, with the inhibition zone of 2 mg/mL POS against these bacteria being 14.3, 19.1, 18.4, and 42.3 mm, respectively. The discrepancies in the results among different studies are probably ascribed to the variations in the molecular structure of POS.

Competitive prevention of pathogens or their toxins from adhering to intestinal mucosa

By relying on the adhesins, gut bacteria can adhere to host intestinal mucosa to resist peristaltic clearance by intestinal tract, eventually establishing long-term colonization and growth in the intestine. Certain functional oligosaccharides have structures similar to bacterial adhesin (or toxin) receptors on IECs and then act as “decoy receptors” to bind to bacterial adhesins or toxins, by which they competitively inhibit intestinal adhesion or toxicity of harmful bacteria (Kong et al., 2022). There were evidences that POS could reduce intestinal toxicity of enterohemorrhagic E. coli O157 by inhibiting its adhesion to IECs and prevent its Shiga toxin from binding to the Gb3 receptor on IECs (Estibaliz et al., 2003; Di et al., 2017). Similarly, Wilkowska et al. (2020) indicated that POS present in beet pulp hydrolysate elevated the adhesion rate of L. brevis and reduced the adhesion rates of several pathogens (e.g. Candida albicans, Candida lusitanie, and Candida pelliculosa) to IECs. Wang et al. (2015) found that POS (2.5 mg/mL) inhibited the adhesion rate of E. coli, S. typhimurium, Vibrio cholerae, and Enterobacter cloacae to IECs by 16.1 %, 98.9 %, 80.6 %, and 95.9 %, respectively. Aside from inhibiting the adhesion of harmful bacteria, POS can directly promote the adhesion of beneficial bacteria such as Bifidobacterium to intestinal mucus layer (Wilkowska et al., 2025), which may also favor to competitively inhibit intestinal adhesion of harmful bacteria and impel gut microbiome becomes more healthy and stable.

Regulation of lipid metabolism

Lipid metabolism is critical for energy harvest, feed conversion efficiency, carcass trait, and meat quality, largely determining the economic profits of animal production. A previous study revealed a tendency of POS addition to increase intramuscular fat content in fattening pigs (Mao et al., 2017a). In laboratory animals, POS was also demonstrated to regulate lipid metabolism and prevent lipid accumulation (Li et al., 2010; Li et al., 2014). These effects are supposed to be achieved through both direct and indirect actions of POS.

Indirect action

Gut microbiome exerts a close connection with host lipid metabolism (Zhong et al., 2025). The metabolites such as SCFA and secondary bile acids produced by gut microbiota can be transported via the portal vein to the liver or other tissues, where they can activate specific receptors with downstream signaling pathways related to lipid metabolism, thus regulating host lipid metabolism (Zhong et al., 2025). An in vitro study showed that the products of gut microbial fermentation of POS promoted cholesterol efflux from macrophages by upregulating liver X receptor (LXR)/ATP-binding cassette transporter (ABC) A1/G1 pathway, as well as inhibited cholesterol synthesis by downregulating the expression of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) (Hu et al., 2021). A study in mice uncovered that dietary POS increased the abundances of beneficial bacteria (e.g. Lactobacillus, Bifidobacterium, and Bacteroides) and SCFA contents in the intestine, which contributed to reduce HMGR activity and elevate cholesterol 7α-hydroxylase activity in the liver, finally facilitating fecal bile acids excretion and lowering cholesterol content in the liver and serum (Hu et al., 2019). Furthermore, POS could alleviate high-fat diet-induced gut microbiota dysbiosis (characterized by reductions of beneficial bacteria like Bifidobacterium and Lactobacillus along with increases in several harmful bacteria) in mice, thereby improving glucose tolerance as well as attenuating hepatic lipid accumulation and steatosis (Yu et al., 2023). Besides the above gut-liver axis, POS may also regulate systemic lipid metabolism through the gut-adipose tissue axis. For example, Fan et al. (2022) reported that incorporating POS to a high-fat diet of mice activated adiponectin-mediated adiponectin receptor 1 (AdipoR1)/adenosine monophosphate-activated protein kinase (AMPK)/peroxisome proliferator-activated receptor α (PPARα) pathway in the adipose tissue. This resulted in elevated expression of enzymes related to lipolysis (e.g. adipose triglyceride lipase, and hormone-sensitive lipase) and fatty acid oxidation (e.g. carnitine palmitoyltransferase 1, and acyl-CoA oxidase), together with reduced expression of enzymes implicated in fatty acid synthesis (e.g. acetyl-CoA carboxylase, and fatty acid synthetase) and triglyceride synthesis (e.g. stearoyl-CoA desaturase 1, and diacylglycerol acyltransferase 1), ultimately diminishing fat deposition inside the body (Fan et al., 2022).

Direct action

Beyond the above indirect action, POS exhibit a potential to directly regulate host lipid metabolism. For example, Hu et al. (2021) found that POS directly accelerated cholesterol excretion from macrophages by elevating the expression of genes in the LXR-ABCA1/ABCG1 pathway, and simultaneously suppressed cholesterol synthesis in macrophages by decreasing HMGR expression.

Modulation of immune responses

Efficient immune responses can eliminate the invaded pathogens along with the aging, damaged or tumorous cells inside the body, thus acting as a prerequisite for the survival and normal growth of animals (Wlaźlak et al., 2023). However, overactive immune responses cause excess production of proinflammatory factors and perturbation of metabolism-related hormones secretion, which trigger inflammatory and oxidative damages concurrent with metabolic disorders and increased expenditure of energy/nutrients in animals (Niu et al., 2022a; Ling et al., 2026). Hence, immune homeostasis is extremely crucial for production performance and health condition of animals. With regard to POS, their effectiveness in regulating immune homeostasis has been established in animals. For example, supplementing POS to Rotavirus-infected piglets could elevate serum immunoglobulin (Ig) G level coupled with the contents of IgA, interferon-γ and Rotavirus antibody in intestinal mucosa (Mao et al., 2019). These effects reinforced intestinal immune defense against Rotavirus and then reduced either the positivity rate (from 100 % to 43 %) of Rotavirus′s non‑structural protein 4 or its content (from 170.13 pg/mg prot. to 119.63 pg/mg prot.) in intestinal mucosa, thus protecting growth performance and health status of piglets from Rotavirus infection (Mao et al., 2017b; Mao et al., 2019). Analogously, there was an evidence that POS ingestion strengthened mucosal immunity to boost the production of IgG, IgA and secretory IgA inside the body, thus protecting against virus-like (Poly I:C) infection in mice (Sori et al., 2022). On the other hand, POS was indicated to decrease the production of pro-inflammatory factors in vivo (Sori et al., 2022) and attenuate intestinal inflammation presumably by suppressing the activation of inflammatory signaling pathways (Tan et al., 2018). The above findings support the role of POS as an immunomodulator in promoting immune homeostasis, which is speculated to be responsible by their indirect and direct actions.

Indirect action

POS can stimulate intestinal cells to produce immune factors such as tumor necrosis factor alpha (TNF-α), interleukin (IL)-10 and Ig, as well as elevate blood Ig concentration through their prebiotic action (Chung et al., 2017), thus fortifying both intestinal and systemic immunity of animals (Zhang et al., 2019; Sori et al., 2022). These effects are favorable for clearing pathogens inside the body and subsequently reducing the production of pro-inflammatory factors (Sori et al., 2022). In addition, intestinal SCFA produced from POS fermentation drive the development of regulatory T (Treg) cells and inhibit the proliferation of T helper 17 cells (Th17, a pro-inflammatory T cell subset), subsequently reducing the production of intestinal inflammatory factors (Zhang et al., 2025). In previous animal trials, POS were corroborated to alleviate gut microbiota dysbiosis caused by high-fat diet and dextran sulfate sodium, which favored to increase SCFA production in the intestine (Wang et al., 2022b; Yu et al., 2023), thus sustaining intestinal Treg/Th17 balance and further mitigating intestinal inflammatory damages (Wang et al., 2022b).

Intestinal fermentation products such as SCFA generated from POS may be transported to other tissues/organs to exert anti-inflammatory effects. An in vitro study evidenced that the fermentation products of POS alleviated LPS-caused sharp upregulations of nuclear factor κB (NF-κB) and pro-inflammatory cytokines (such as IL-6 and TNF-α), which in turn facilitated macrophage polarization towards M2 phenotype (Hu et al., 2021). Furthermore, the fermentation products of POS was indicated to attenuate macrophages inflammation induced by palmitoylated 3-hydroxy-4-mercaptoserine-lysine-4 (a potent Toll-like recepror (TLR)-2 agonist mimicking the lipoproteins in bacterial cell wall) and simultaneously promote macrophages M2 polarization (Hu et al., 2021). A study in mice revealed that POS alleviated high-fat diet-induced increase in inflammatory cytokine (e.g. TNF-α) content in adipose tissue (Fan et al., 2022). Similarly, Li et al. (2019b) observed that supplementing POS to a high-fat diet of mice lowered the expression of hepatic NF-κB-inducing kinase, inhibitor of NF-κB (I-κB) kinase (IKK) and TNF-α, as well as increased hepatic expression of anti-inflammatory signaling molecules, such as adenosine monophosphate-activated protein kinase (AMPK) and silent information regulator 1 (SIRT1). These actions could further repress inflammatory pathway activation and inflammatory cytokines production as well as prompt the production of anti-inflammatory cytokines (e.g. IL-10) in the liver, ultimately alleviating liver inflammation (Li et al., 2019b).

Direct action

The immunomodulatory effects of POS are not entirely dependent on shaping gut microbiome, POS themselves can directly regulate immune responses. For instance, POS treatment was found to mildly stimulate the production of nitric oxide (NO) without lowering the viability of macrophages (Singh et al., 2020; Yeung et al., 2021), as well as moderately elevate the expression of pro-inflammatory cytokines (IL-6 and TNF-α) and anti-inflammatory cytokine IL-10 in macrophages (Hu et al., 2021). By using an inhibitor (TAK-242) of TLR4, Wang et al. (2022a) confirmed that POS stimulated NO, IL-6 and TNF-α production in macrophages by activating the TLR4 on cell surface, however, this action did not reduce but rather increased cell viability. The above findings imply that POS confer a mild stimulation to TLR4 pathway. Intriguingly, POS were also found to block LPS-induced phosphorylation of IKK and degradation of IκBα in macrophages, which in turn lowered the phosphorylation level of NF-κB p65 and alleviated the overproduction of inflammatory mediators including NO, inducible nitric oxide synthase (iNOS), and pro-inflammatory cytokines (such as IL-1β, IL-6 and TNF-α) (Singh et al., 2020; Yeung et al., 2021). Likewise, other study also verified an ability of POS to restore the sharp upregulations of NF-κB and the aforementioned pro-inflammatory mediators caused by LPS in macrophages, while weakening the inhibitory effect of LPS on M2 polarization of macrophages (Hu et al., 2021). Based on the above findings, it can be speculated that POS bind to cell surface TLR4 or its accessory proteins (e.g. myeloid differentiation protein 2, MD-2) in a gentle manner (Ling et al., 2026), which mildly activate cellular immune responses without triggering inflammation, thus reinforcing immune defences of host cells (as illustrated in Fig. 3). Due to the interaction of POS with TLR4 or its accessory proteins, POS seem to competitively inhibit LPS-caused overactivation of TLR4 pathway and subsequently attenuate cellular inflammation (as illustrated in Fig. 3). Analogously, our previous study indicated a potential of D-GalA (the basic unit of POS) to bind to the cluster of differentiation antigen 14 (CD14), an another accessory protein assisting in presenting LPS to TLR4, causing a moderate activation of immune response (manifested as a mild increase in the expression of TLR4, CD14 and some inflammatory factors) in macrophages (Li et al., 2025). By using the inhibitors of TLR4 and NF-κB p65, D-GalA was further substantiated to reverse the intense activation of TLR4/NF-κB pathway by LPS, consequently mitigating the excess expression of inflammatory factors and apoptosis in macrophages (Li et al., 2025).

Fig. 3.

Immunomodulatory and anti-inflammatory effects of pectic oligosaccharides (POS). LPS, lipopolysaccharide; CD14, cluster of differentiation antigen 14; MD-2, myeloid differentiation protein 2; TLR4, Toll-like receptor 4; MyD88, myeloid differentiation antigen 88; TIRF, Toll/interleukin-1 receptor-domain-containing adapter-inducing interferon-β; TAK1, transforming growth factor-β-activated kinase 1; IKKs, inhibitor of NF-κB kinases; IκB, inhibitor of nuclear factor kappa B. LPS binds to the TLR4/MD2 receptor complex on the cell membrane with the assistance of the CD14. This binding triggers downstream signaling activation via the MyD88-dependent and TRIF-dependent pathways, which converge at the activation of the TAK1. The activated TAK1 further activates the IKK complex that can phosphorylate the inhibitory protein IkBα, leading to its ubiquitination and degradation. This process releases the NF-κB heterodimer (p50-p65), allowing the phosphorylated p65 subunit to translocate into the nucleus, subsequently initiating the transcription of inflammatory factors. POS may competitively inhibit the recognition of LPS by TLR4/MD2 receptor complex through binding to the accessory protein (such as MD2) of TLR4, thereby suppressing the activation of the downstream signalings and alleviating LPS-induced overproduction of inflammatory factors. POS alone may also mildly activate the TLR4/NF-κB pathway and promote the production of inflammatory factors, through moderately stimulating the accessory protein (such as MD2) of TLR4.

In addition to anti-inflammation, POS also exhibit direct anti-allergic property. Ma et al. (2022) discovered that POS inhibited IL-4 production and in turn reduced IgE (a core inducing factor of allergic reactions) secretion with its induction of extracellular calcium ion influx in RBL-2H3 cells (a rat basophilic leukemia cell line capable of simulating the functions of mast cells and basophilic granulocytes). These actions finally limited cell degranulation and the subsequent release of allergic mediators such as β-hexosaminidase and histamine (Ma et al., 2022). Likewise, the ability of POS to inhibit IgE production in U266 cells (a human myeloma cell line) was also described elsewhere (Pattarapisitporn et al., 2024). The above findings reveal the potential of POS to directly elicit anti-allergic action that may benefit poultry production, because the allergic responses caused by certain dietary antigens (e.g. soybean glycinin and β-conglycinin) lead to impairments in growth performance, carcass composition and meat quality, concurrent with intestinal discomforts such as poor nutrient utilization and barrier dysfunction in poultry (Osman et al., 2020; Du et al., 2025).

Antioxidant activity

Modern poultry species such as the fast-growing broiler chickens and laying hens with high egg production have robust metabolism with high demand for energy supply via mitochondrial respiration and oxidative phosphorylation, during which considerable free radicals are naturally produced. Moreover, dietary factors (e.g. oxidized oils, high-energy and high-fat diets), environmental stresses (e.g. high-density rearing, heat stress and ammonia exposure) and immunological challenges (e.g. vaccination, antigen exposure and pathogen invasion) aggravate the overgeneration of free radicals, which perturb redox balance and cause oxidative stress inside the body, thus impairing production performance and health status of poultry (Oke et al., 2024; Barbarestani et al., 2025). Regarding POS, their ability to enhance antioxidant activity and alleviate oxidative stress in animals has been verified. For example, it was reported that POS addition increased serum total antioxidant capacity (T-AOC) as well as decreased malondialdehyde (MDA) content in serum and intestinal mucosa, thus mitigating intestinal oxidative stress in Rotavirus-infected piglets (Chen et al., 2017; Mao et al., 2017b; Mao et al., 2019). These benefits achieved by POS contributed to lower the expression of autophagy-related proteins (e.g. endoplasmic reticulum stress-induced transcription factor (CHOP) and Beclin-1) and pro-apoptotic protein (Bcl2-associated X protein, Bax) as well as promote the phosphorylation of autophagy-inhibitory protein such as mammalian target of rapamycin (mTOR) in the intestine, which ultimately weakened intestinal cell autophagy and apoptosis of piglets (Mao et al., 2017b). Through alleviating oxidative stress, POS addition was further found to mitigate Rotavirus-induced decreases in intestinal digestive enzymes (e.g. amylase, lipase, and trypsin) activities (Chen et al., 2017), destruction of intestinal villus-crypt architecture, along with reduction of intestinal tight junction proteins (e.g. claudin-1, claudin-3, occludin and ZO-1) and mucins (e.g. mucin-1 and mucin-2) expression (Mao et al., 2017b; Mao et al., 2019). The above findings collectively suggest that POS exert antioxidant effect against intestinal oxidative damages, which can be associated with their indirect and direct actions.

Indirect action

POS-originated SCFA especially butyrate can facilitate histone acetylation and activate Kelch-like ECH-associated protein 1(Keap1)/ nuclear factor erythroid 2-related factor 2 (Nrf2) pathway or AMPK/Nrf2 pathway, by binding to G-protein-coupled receptors (GPR) on host cell surface (Guo et al., 2020; Li et al., 2021b). These actions lead to upregulated expression of multiple antioxidases (e.g. catalase, and glutathione peroxidase) and then potentiate antioxidant capacity to alleviate intestinal oxidative stress (Ferrer et al., 2024). Besides, SCFA may entry into extraintestinal tissues via portal vein, probably fortifying systemic antioxidant capacity. In support of this view, certain studies have indicated the ability of POS to repress high-fat diet-induced oxidative stress by increasing superoxide dismutase (SOD) activity and decreasing MDA production in both serum and liver of mice (Li et al., 2010; Li et al., 2014). Similarly, Liu et al. (2020) described a role of dietary POS in elevating serum T-AOC and placental SOD activity as well as in reducing MDA content in both serum and placenta in rats.

Direct action

The hydroxyl and other functional groups in POS molecules may undergo chelation reactions with certain metal ions (e.g. iron and copper ions) and then form relatively stable complexes, thereby blocking the Fenton reaction caused by metal ions and reducing the conversion of hydrogen peroxide into more toxic hydroxyl radical (OH·) (Yeung et al., 2021). Additionally, the reactive groups like hydroxyl and aldehyde groups in POS molecules can capture free radicals and convert them into stable molecules, thus inhibiting the resultant chain reactions (Yeung et al., 2021). By employing the 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging assays as well as the ferric reducing/antioxidant power assay, growing studies have confirmed the free radical-scavenging capacity of POS that was stronger than that of fructo-oligosaccharide and inulin (Del Amo-Mateos et al., 2024; Wilkowska et al., 2025). Likewise, Yeung et al. (2021) reported that POS (5 mg/mL) with different MW had clearance rates of 54.09 %, 61.85 % and 91.01 % for DPPH. Amini-Rourani (2025) reported that POS at various concentrations (1.25∼10 mg/mL) had DPPH-clearance rates ranging from 18 % to 90 %. Our previous investigation also revealed the clearance effects of POS on DPPH, OH·, and superoxide anions (O₂·^-) (Ye et al., 2025). Although the clearance effect of POS on O₂·^- was relatively weak, their clearance effects on DPPH and OH· intensified markedly at a concentration higher than 0.8 mg/mL, with the clearance rates of DPPH and OH· by 6.4 mg/mL POS exceeding 90 % and 70 %, respectively (Ye et al., 2025). In the study of Wang et al. (2021a), POS was observed to reduce the acid value and peroxide value of an oxidized diet by approximately 50 %. Further research disclosed that supplementing POS to the oxidized diet of rats increased SOD activity and T-AOC as well as reduced MDA content in the intestine, which subsequently alleviated intestinal oxidative stress and conduced to attenuate the resultant structural destruction and pathological injuries of the intestine (Wang et al., 2021a).

Anti-tumor activity

The infection by specific viruses such as Marek's disease virus and avian leukosis virus often triggers malignant proliferation and transformation of host cells especially in susceptible chickens, resulting in the formation of various tumors (such as leiomyoma, adenocarcinoma and lymphomas) that can occur in multiple organs including the intestine (Tomásek et al., 2005; Cheng et al., 2010; Stamilla et al., 2020). These adverse outcomes bring about abnormities in intestinal physiology and immune responses accompanied by increased mortality in poultry (Cheng et al., 2010; Stamilla et al., 2020). Previously, POS were reported to exert no impact on the viability of normal cells such as mouse fibroblasts (L-929 cells) and human umbilical vein endothelial cells (HUVEC cells) (Amini-Rourani et al., 2025). However, POS could decrease the expression of anti-apoptotic protein galectin-3 and its downstream key protein (survivin) in mouse melanoma cells (B16F10 cells), thus inhibiting the proliferation and accelerating the apoptosis of these tumor cells (Mallikarjuna et al., 2018). In human breast cancer cells (MCF-7 cells), POS were also detected to inhibit cell proliferation and promote cell apoptosis by decreasing galectin-3 expression and increasing pro-apoptotic factor Bax expression (Li et al., 2019a; Amini-Rourani et al., 2025). Likewise, other studies depicted the role of POS in suppressing the proliferation of colorectal adenocarcinoma cells (HT29 and Caco-2 cells) (Rajulapati et al., 2021; Amini-Rourani et al., 2025), as well as activating caspase-3 activity and DNA laddering degradation (a mark of apoptosis) of HT-29 cells (Olano-Martin et al., 2003). Interestingly, POS may also exert in vivo anti-tumor effect by modulating oxidative stress- and inflammation-related signalling pathways (Tan et al., 2018). The above findings imply a contribution of POS to the therapy against tumors in the intestine or other organs, probably favoring to improve poultry welfare and reduce economic losses in production.

Relationships between raw material sources and biological activities of POS

POS prepared from different raw material sources have discrepancies in their bioactivities (Singh et al., 2020; Zwolschen et al., 2024). For example, Wang et al. (2022c) prepared POS from orange peel pectin and apple pulp pectin, and found that the inhibition zone of the former POS against bacteria (E. coli, S. typhimurium, S. aureus, and M. luteus) was larger than that of the latter POS. Compared with orange peel-sourced POS, orange fruit-sourced POS (containing higher proportion of D-GalA) exhibited greater ability to facilitate the growth of Lactobacillus spp. (L. reuteri and L. acidophilus) and their production of lactate, concomitant with the production of propionate by Lactobacillus spp. (L. bulgaricus, L. reuteri, L. acidophilus, and L. lactis) (Thikham et al., 2023). Relative to beet pulp-sourced POS, waste red beetroot-sourced POS displayed higher efficacy to boost the growth of L. rhamnosus and B. longum as well as shorten their generation time, together with stronger antioxidant property including free radicals (DPPH and ABTS)-scavenging and ferric ion-reducing capacities (Del Amo-Mateos et al., 2024). The influences of raw material sources on the bioactivities of POS may be realized by associating with the corresponding variation of the molecular structure of POS.

Structure-activity relationships of POS

Influences of the MW or DP on biological activities of POS

Because of the varying capacities to secrete carbohydrases and the related transporters, different beneficial bacteria possess distinct preferences for degrading POS with different MW or DP (de Alencar et al., 2025). Generally, POS with lower MW are more easily fermented and thus more readily exert the prebiotic effects (Singh et al., 2020). Yeung et al. (2021) prepared POS with different MW (6.09, 4.89, and 1.79 kDa) and found that POS with smaller MW caused faster growth of L. rhamnosus with higher production of SCFA (particularly acetate), while also stimulating Bifidobacterium to produce more propionate. Vásquez et al. (2024) prepared POS with different MW (<3 kDa, 3–10 kDa, >10 kDa) and detected that POS with the smallest MW had the highest efficacy in promoting the growth of L. casei and inhibiting E. coli growth. However, the prebiotic efficacy of POS is not linearly related to their MW. This can be supported by the study of Li et al. (2016), who prepared POS with different MW (<1 kDa, 1–3 kDa, >3 kDa) and observed that POS with a MW of 1–3 kDa exhibited the strongest prebiotic action (namely the ability to promote the growth of Lactobacillus and Bifidobacterium).

Beyond influencing the prebiotic effects, MW or DP also affect other activities of POS. For example, Li et al. (2016) reported that POS with a MW >3 kDa showed weaker antibacterial activity against E. coli, S. aureus and Bacillus than POS with a MW < 3 kDa. Li et al. (2019a) discovered that the efficacy of POS in inhibiting the proliferation of MCF-7 cells increased as the MW decreased. Wilkowska et al. (2025) found that the ability of POS to scavenge DPPH and ABTS radicals increased as the MW decreased from over 10 kDa to under 1 kDa). Yeung et al. (2021) observed that POS with smaller MW in the range of 1.79–6.09 kDa exhibited higher scavenging rates for DPPH and ABTS radicals together with greater inhibitory effect on LPS-induced stimulation of NF-κB pathway and inflammatory mediators (e.g. iNOS and IL-6) expression in macrophages. In the research of Pattarapisitporn et al. (2024), POS with a DP of 2 (i.e. trigalacturonic acid) showed higher efficacy in alleviating IgE-mediated allergic responses in RBL-2H3 cells compared to POS with a DP of 3 (i.e. digalacturonic acid).

Influences of backbone modification on biological activities of POS

The hydroxyl groups at the C-2 or C-3 of the D-GalA residues on the backbone of POS are prone to acetylation, while the carboxyl group at C-6 can be methyl-esterified. These modifying groups may create spatial hindrance and then hamper the cleavage of glycosidic bonds of POS by certain enzymes. There was an evidence that acetylation reduced the fermentation rate of POS by fecal microbiota (Leijdekkers et al., 2014), whilst methyl-esterification could delay the fermentation process of POS by gut commensals (e.g. C. butyricum) probably via slowing the uptake and cellular transport of POS (Zwolschen et al., 2024). However, the total production of SCFA from gut microbial fermentation of methyl-esterified POS was detected to be higher than that of non-esterified POS (Zwolschen et al., 2024), which might be ascribed to the cross-feeding of methyl-esterified POS within gut microbiota. During the fermentation of methyl-esterified POS, the methanol released from the methoxycarbonyl might be oxidized to formaldehyde by specific gut microbes (Ishaq et al., 2016). The resulting formaldehyde could be further transformed into acetate by certain commensal bacteria such as the Blautia (Dorokhov et al., 2015; Pietzke et al., 2020). Similarly, Singh et al. (2020) revealed that highly methyl-esterified POS seemed to be more efficient in promoting the growth of beneficial bacteria (e.g. Bifidobacterium, Ruminococcus, and Roseburia) as compared to low methyl-esterified POS.

The methyl-esterification neutralizes the negative charge carried by the carboxyl group of D-GalA residues in the backbone of POS, which may diminish the intermolecular electrostatic repulsion and alter the chain conformation of POS molecules. This alteration is assumed to shift the interactions of POS with bacterial cell surface components or their toxins (Liu et al., 2023), probably impacting the efficacy of POS. Indeed, Wang et al. (2022c) revealed stronger antibacterial activities of methyl-esterified POS against E. coli, S. typhimurium, S. aureus and M. luteus than non-esterified POS. On the contrary, Estibaliz et al. (2003) found that POS with a higher degree of methyl-esterification were less effective in blocking the binding of Shiga toxin of E. coli O157:H7 to IECs.

Influences of backbone saturation on biological activities of POS

Pectin lyase cleaves glycosidic bonds on the backbone of pectins through β-reduction reactions, forming an unsaturated uronic acid residue at the non-reducing end of the generated POS. An in vitro fermentation experiment indicated that saturated POS were fermented rapidly by gut microbiota to produce SCFA, with a preference towards the production of propionate (Zwolschen et al., 2024). In contrast, it was reported that the fermentation of unsaturated POS by gut microbiota was relatively slow but more favorable for promoting the growth of C. butyricum with the production of butyrate (Zwolschen et al., 2024).

Influences of side chain groups on biological activities of POS

It appears that side chain groups of POS mainly influence their prebiotic and immunoregulatory activities. Compared with RG-I-derived POS that possess abundant side chain groups, HG-derived POS containing few side chain group was revealed to be more easily fermented by gut microbiota (Leijdekkers et al., 2014), as well as being more efficiently in promoting the growth of beneficial gut bacteria (e.g. Bifidobacterium, Ruminococcus, and Roseburia) and mitigating the overproduction of inflammatory cytokines (IL-6 and TNF-α) in macrophages stimulated by LPS (Singh et al., 2020). Conversely, compared with POS derived from natural pectins possessing abundant side chain groups, POS derived from pectic acid that lacks side chain groups showed an disadvantage in moderately activating TLR4 pathway with the resultant production of immune factors (e.g. IL-6, TNF-α, and NO) in macrophages free of stimulation (Wang et al., 2022a).

Current application of POS in poultry production

At present, there are relatively more researches on the application of POS in broilers (including broiler breeders and broiler chickens) instead of other poultry species.

Application in broiler breeder production

POS demonstrates promising application effects in broiler breeders. Several previous studies indicated that dietary supplementation with 200 mg/kg POS (30 % purity) increasesd egg production (Mao et al., 2021) and egg weight (Zhao et al., 2019; Mao et al., 2021; Wang et al., 2021b) of broiler breeders, while reducing their feed-to-egg ratio (Wang et al., 2021b). It also improved egg quality parameters, including albumen height and Haugh unit of the hatching eggs (Zhao et al., 2019; Wang et al., 2021b). In addition to production performance, POS are also effective in ameliorating the health status of broiler breeders. For example, Mao et al. (2021) reported that supplementing POS (200 mg/kg, 30 % purity) to broiler breeders with low egg production elevated jejunal SOD activity and zonula occluden 1 (ZO-1) expression, as well as alleviated the increases in jejunal MDA content coupled with IL-6 and TNF-α expression. Wang et al. (2021b) observed reductions in serum inflammatory cytokines (IL-1β and IL-8) and ovarian MDA contents in broiler breeders supplemented with POS (200 mg/kg, 30 % purity), which simultaneously increased SOD activity in the ovary and oviduct magnum along with ovarian T-AOC. Further investigation manifested that feeding POS elevated the expression of anti-apoptotic protein Bcl-2 and proliferating cell nuclear antigen as well as attenuated the increased expression of pro-apoptotic proteins (caspase-9 and Bax) in the ovary of broiler breeders with low egg production (Wang et al., 2021b). Comprehensively, the above findings support the roles of dietary POS in fortifying intestinal and ovarian antioxidant property coupled with intestinal barrier function, as well as in inhibiting ovarian cell apoptosis. These benefits may contribute to improve intestinal and ovarian health of broiler breeders especially those with low egg production, ultimately ameliorating their reproductive performance and albumen quality.

The beneficial effects of POS on intestinal and ovarian health of broiler breeders may be partially explained by their prebiotic action. This is supported by the finding by Mao et al. (2021) who detected a capacity of POS addition (200 mg/kg, 30 % purity) to optimize gut microbial composition of broiler breeders and increase the abundance of certain beneficial bacteria (e.g. Phascolarctobacterium) in gut. Phascolarctobacterium can inhibit the succinate receptor/NF-κB signaling pathway by consuming succinate, consequently lowering the expression of inflammatory factors and relieving intestinal inflammatory damages (Huo et al., 2025). Moreover, due to the ability to produce SCFA in intestinal lumen (Zhou et al., 2023), Phascolarctobacterium may increase the transportation of SCFA from the intestine to the ovary, presumably conducing to improve ovary functions and reproductive performance of broiler breeders (Yu et al., 2025). Thus, the enrichment of intestinal beneficial bacteria by POS may contribute to improve the health of broiler breeders.

Application in broiler chicken or other poultry species production

POS elicit positive effects on growth performance and intestinal health of broiler chickens potentially through their antioxidant and anti-inflammatory actions. Our recent research indicated that supplementing 400 mg/kg POS (92 % purity) to the diet of broiler chickens tended to increase average daily gain (ADG) and average daily feed intake (ADFI), as well as alleviated aflatoxin B₁ (AFB₁)-induced increases in spleen index and serum alanine aminotransferase activity concomitant with a decline in bursa of Fabricius index (Ye et al., 2025). Moreover, an increasing trend of ileal T-AOC together with elevations in ileal glutathione content and claudin-1 expression in AFB₁-exposed broiler chickens were observed in response to POS supplementation, which also decreased the levels of ileal reactive oxygen species and serum diamine oxidase (a biomarker of intestinal barrier damage) (Ye et al., 2025). The above findings suggest that POS have ameliorative effects on growth performance, organ indexes coupled with intestinal redox status and barrier function of broiler chickens exposed to AFB₁. In a later research, we found that supplementing 600 mg/kg POS (92 % purity) to the diet of broiler chickens reversed LPS-induced declines in growth performance (average body weight, ADG), abnormities in organ indexes (e.g. thymic atrophy, hepatomegaly), concurrent with increased levels of inflammatory cytokines (e.g. IL-1β, IL-6) and serum biomarkers (such as diamine oxidase and endotoxin) of intestinal barrier disruption (Ling et al., 2026). Further examination disclosed that POS addition (600 mg/kg, 92 % purity) relieved LPS-caused intestinal villus atrophy, reductions in intestinal goblet cell count and tight junction proteins (e.g. claudin-1, ZO-1) expression, together with increases in the expression levels of pro-apoptotic proteins (e.g. caspase-3, Bax) and inflammatory factors (e.g. IL-1β, IL-6, TLR4, and NF-κB p65) in broiler chickens (Ling et al., 2026). Intriguingly, integration of molecular docking simulation and microscale thermophoresis evidenced an ability of POS to bind to MD-2 (which forms a complex with TLR4 to recognize and bind to LPS) on intestinal cell surface (unpublished findings). Through the above action, POS might competitively repress the overactivation of intestinal TLR4/NF-κB pathway triggered by LPS, subsequently alleviating intestinal inflammation and barrier damage in broiler chickens (Li et al., 2025; Ling et al., 2026).

Besides antioxidant and anti-inflammatory actions, POS have the potential to enhance absorption and utilization of nutrients particularly the minerals that may conduce to improve growth performance and health status of broiler chickens. In support of this viewpoint, Wang et al. (2019a) indicated that supplementation of 482 mg/kg POS (30 % purity) increased pancreatic zinc (Zn) and metallothionein (a Zn-containing antioxidant protein) levels together with serum T-AOC, duodenal villus height, cecal isobutyrate content and growth performance (ADG and final body weight) of broiler chickens, while reducing their mortality. The reasons why POS promote Zn utilization in broiler chickens may be as follows. On one hand, POS facilitate SCFA production by beneficial gut bacteria, which lowers intestinal pH and increases the solubility of Zn ions. On the other hand, the carboxyl groups on POS molecules may form chelates with trace elements through ionic bonds, which likely diminish the antagonism from other metal ions on Zn ions. In support of this viewpoint, Wang et al. (2019b) supplemented different doses (0, 200, 400 and 800 mg/kg) of POS chelated Zn (POS-Zn, containing 7 % Zn) to the diet of broiler chickens, with total dietary Zn level equalized across different groups by supplementing Zn sulfate (ZnSO₄). The results showed that increasing POS-Zn in diet linearly or quadratically upregulated the expression of pancreatic Zn transporters, including Zn transporter (ZnT)-1, ZnT-2, metallothionein, and metal-responsive transcription factor 1. It also linearly or quadratically increased serum zinc-containing enzymes (such as alkaline phosphatase and Cu/Zn-SOD) activities along with hepatic and pancreatic metallothionein content, as well as linearly improved growth performance (ADG, ADFI and feed conversion efficiency) and linearly reduced leg disorder incidence in broiler chickens (Wang et al., 2019b). The superiorities of POS-Zn over ZnSO₄ were also described elsewhere. For example, compared with an equivalent dose of ZnSO₄ (based on dietary Zn level), supplementation of 300 mg/kg POS-Zn enhanced serum SOD and catalase activities in broiler chickens (Wang et al., 2016a), while supplemental 600 mg/kg POS-Zn elevated hepatic Zn deposition and dietary nutrients (dry matter and crude protein) digestibility (Wang et al., 2016b), together with ADG and ADFI of broiler chickens (Wang et al., 2016a; Wang et al., 2016b). Likewise, compared to an equivalent dose of ZnSO₄ (based on dietary Zn level), supplemental 800 mg/kg POS-Zn increased egg production, average egg weight, egg yolk color as well as Zn and iron accretion in eggs to a certain extent (Wang et al., 2017). The above findings demonstrate that POS-Zn propel Zn absorption and its enrichment in metabolic organs, thus enabling the improvements of production performance and antioxidant functions in chickens.

Limitations and future directions

Despite the progress on POS research in animal nutrition, there are still several limitations or challenges regarding the wide acceptance of POS as a sustainable additive applied in poultry diets.

Challenge in the standardized production of POS

The structure of POS is highly dependent on raw material sources (Wang et al., 2022a; Thikham et al., 2023; Del Amo-Mateos et al., 2024) and preparation methods (Pattarapisitporn et al., 2024). Despite the extensive studies in in vitro models, there is a lack of information about the structure-function relationships of POS in poultry production, which remains to be established in future research. Moreover, since structural modifications represent a crucial approach to increase the bioactivities of oligosaccharides (Li et al., 2021a), the potential increase in the application efficacy of POS by chemical modifications such as the phosphorylation (as depicted in Fig. 4) is worthy to be verified in poultry production. Such research efforts are anticipated to drive the standardized production of targeted POS products with high efficacy.

Fig. 4.

Phosphorylation modification of oligogalacturonic acid (a narrow-sense pectic oligosaccharide) with degree of polymerization of 2 to 20. This Fig. was created with the help of ChemDraw software.

Inadequate understanding about the bioefficacy and specific mechanisms of POS in poultry

Poultry possess distinct anatomical and physiological features of the gastrointestine compared to mammals, which may cause differences in gut microbial composition and fermentation patterns between poultry and mammals (Stanley et al., 2014). Moreover, lipid metabolism (Wang et al., 2023) and immune responses (Kogut et al., 2020) of poultry exhibit species-specific features. Consequently, the prebiotic effects of POS and the systemic effects of POS-fermented metabolites in mammals may not be identical in poultry (Markowiak and Śliżewska, 2018; Atuahene et al, 2025). Therefore, although mammalian and in vitro studies have provided evidences for multiple bioactivities of POS, these benefits and their specific mechanisms need to be validated in poultry. In future studies, metagenomics and culturomics are warranted to be adopted to identify which specific strains of beneficial bacteria in poultry gut are enriched by dietary POS. Meanwhile, it deserves to integrate intestinal organoids with multi-omics analysis to systematically elucidate the molecular mechanisms by which POS improve the cross-talks between gut microbiota and intestinal tissues of poultry at the transcript, protein, and metabolite levels. Furthermore, intermolecular interaction detecting techniques (such as microscale thermophoresis, surface plasmon resonance) combined with circular dichroism spectroscopy are suggested to be employed, in order to clarify how POS interact with the pattern recognition receptor on cell surface to trigger cellular immune signal transduction inside the body of poultry. The above investigations will strengthen the mechanistic basis for long-term application of POS in poultry production.

Limited knowledge concerning the precise application schemes of POS in poultry production

Different studies display an obvious difference in the addition amount of POS in poultry diet, and the dose-responses of dietary POS are not yet fully expounded. In future studies, it is necessary to investigate the appropriate, cost-optimal and maximum addition amount of POS in the diets of different poultry species under different production stages and physiological status. On the other hand, the structure-activity relationships of POS in poultry production remain unclear, although they have been established in mammals or in vitro models. Future studies need to explore the structure-activity relationships of POS for promotion of growth and health of poultry. Moreover, current researches on POS mainly focus on their individual functions, with almost no studies concerning the combined usage of POS with other additives (especially the probiotics). Future studies should place an emphasis on detecting the beneficial effects of synbiotics formed by POS and specific probiotic strains capable of eliciting synergy with POS in poultry nutrition. These strategies are believed to provide solid foundations for precisely applying POS in poultry production and maximizing its economic profits.

Conclusions

As an emerging class of functional oligosaccharides prepared from diverse natural sources, POS can improve gut microbiota via both prebiotic and non-prebiotic actions, as well as display many other bioactivities, including improvements of lipid metabolism and immune defenses along with anti-inflammation and antioxidation. In animal production, the application of POS exhibites substantial benefits, such as improving production performance, product quality, intestinal and genital health. Given these remarkable effects together with the advantages (extensive source, low cost and safety), POS hold great promise as a novel sustainable additive in poultry diets. Future researches ought to prioritize the elucidation of specific mechanisms for the beneficial effects of POS on poultry growth and health. In order to corroborate the practicality and maximize the benefits of POS, it deserves to explore the dose-responses of POS across various poultry species under different growth/production stages or physiological status, as well as their structure-function relationships and collaboration application with certain other additives in poultry diets. Such strategies will facilitate to fully exploit the potential of POS as a practicable and cost-efficient additive to propel poultry production with antibiotic-free diets.

CRediT authorship contribution statement

Weiwei Wang: Writing – original draft, Funding acquisition, Conceptualization. Songtao Liu: Visualization, Software. Shitang Zhang: Methodology. Yan Li: Visualization. Jianjun Zuo: Writing – review & editing, Supervision.

Disclosures

We declare that we have no financial and personal relationships with other people or organizations that can have appeared to impact the work presented in this paper.