Plant bioactive compounds as functional feed additives for improving livestock and poultry production: review

Article information

Anim Biosci. 2026;39.250961

Publication date (electronic) : 2026 June 24

doi : https://doi.org/10.5713/ab.250961

Do Thi Cat Tuong ¹^,^a

, Adhimoolam Karthikeyan ²^,^a

, Lin Lat La Min ¹

, Sureshbabu Anjana ¹

, Masayuki Funaba ³

, Sanggun Roh ⁴^,

, Taesun Min ¹^,

¹Department of Animal Biotechnology, Jeju International Animal Research Center, Sustainable Agriculture Research Institute, Jeju National University, Jeju, Korea

²Jeju International Animal Research Center, Jeju National University, Jeju, Korea

³Division of Applied Biosciences, Graduate School of Agriculture, Kyoto University, Kyoto, Japan

⁴Graduate School of Agricultural Science, Tohoku University, Sendai, Japan

^*Corresponding Author: Sanggun Roh, Tel: +81-22-757-4121, E-mail: sanggun.roh.a3@tohoku.ac.jp. Taesun Min, Tel: +82-64-754-3335, E-mail: tsmin@jejunu.ac.kr

aThese authors contributed equally to this work.

Received 2025 December 6; Revised 2026 January 18; Accepted 2026 June 17.

Abstract

The administration of antibiotics to enhance growth and prevent diseases in livestock and poultry has elicited concerns over antimicrobial resistance and its implications for public health. The escalating demands on the livestock and poultry sectors necessitate enhanced productivity, diminished economic losses, and the guarantee of food safety for human consumption. Plant bioactive compounds (PBCs) have developed as safe and sustainable alternatives to antibiotics that enhance growth, bolster animal health, and boost productivity without jeopardizing food safety. PBCs represent a diverse group of secondary metabolites—including phenolics, terpenoids, polysaccharides, and organosulfur compounds—that exhibit a wide range of biological activities relevant to livestock and poultry nutrition and health. Recent studies have shown that supplementing animals with PBCs as feed additives, either as crude extracts or individual compounds, improves growth performance, nutrient utilization and modulates gut microbiota, while exerting antioxidant, anti-inflammatory, antimicrobial, and immunoregulatory effects, and thereby enhancing overall resilience of animals. The multifunctional properties of PBCs, along with the reduced risk of resistance development, position them as promising candidates for next-generation feed additives for livestock and poultry production. However, challenges remain regarding optimal concentration, variability in bioavailability, stability during feed processing, and the standardization of active components. Here, we discuss the major PBCs and their potential as functional feed additives to improve livestock and poultry production. We further highlight research gaps and outline future prospects required to promote their integration into sustainable animal production.

Keywords: Antibiotics; Phytogenic Feed Additives; Ruminant and Monogastric Nutrition; Sustainable Livestock Production

INTRODUCTION

Antibiotics were initially introduced to treat infections in livestock and poultry, were later found to promote weight gain, which led to their widespread use as growth promoters in livestock and poultry farming over the past decades. However, the prolonged use of antibiotics in animals has raised significant concerns, including the emergence of antimicrobial resistance, the disruption of gut microbiota, and the potential transfer of resistant pathogens to humans through the food chain [1,2]. In recent years, growing awareness of the risks associated with antibiotic overuse has influenced consumer preferences. Modern consumers increasingly demand food products that are safe, natural, and free from antibiotic residues, driving the livestock and poultry industries to adopt more sustainable production practices [3]. In addition to consumer awareness, government regulations and policy interventions have played a pivotal role in promoting the reduction of antibiotic dependence in livestock and poultry production [4]. Many countries, particularly within the European Union, have already banned antibiotics as growth promoters, with similar restrictions being progressively implemented worldwide [5]. These challenges have driven a global search for safe and sustainable alternatives to antibiotics.

Plant-derived bioactive compounds (PBCs)—including phenolics, terpenoids, polysaccharides, and organosulfur compounds (OSCs)—have gained considerable attention as natural growth promoters and health modulators in livestock and poultry production. PBCs are naturally occurring secondary metabolites of plants that influence biological processes in living organisms, providing benefits beyond their basic nutritional functions [6,7]. Their multifaceted properties, including antioxidant, anti-inflammatory, antimicrobial, and immunomodulatory activities [8], make them promising candidates to replace or reduce the reliance on antibiotics and conventional feed additives in livestock and poultry farming. The beneficial effects of PBCs include the protection of dietary proteins from excessive degradation through the activity of tannins or polyphenol oxidase, which lowers soluble nitrogen levels and enhances nitrogen utilization efficiency in animals [9]. These compounds also contribute to reducing pollutant emissions, such as methane, while enhancing overall animal health and resilience. PBCs are increasingly recognized for their inherent benefits, characterized by reduced toxicity, low residue formation, a reduced risk of drug resistance development and enhanced safety [10]. However, some PBCs—even those considered beneficial at optimal levels—can exert anti-nutritional or toxic effects when present at inappropriate concentrations. Despite extensive research on PBCs in livestock and poultry nutrition, their efficacy and use remain inconclusive and limited. Addressing knowledge gaps requires interdisciplinary efforts to achieve economically viable, environmentally sustainable and eco-friendly animal production. In this review, we first discuss major PBCs, their sources, and mechanisms of action, followed by the potential of PBCs to improve animal performance, nutrition, health and product quality in livestock and poultry.

We further discuss existing research gaps and outline future perspectives necessary for their effective application in sustainable animal production. Relevant literature was collected from Web of Science, Scopus, and PubMed using keywords related to PBCs and livestock and poultry production. Priority was given to peer-reviewed, recent, and high-quality studies relevant to animal health and productivity.

PLANT-DERIVED BIOACTIVE COMPOUNDs: CLASSIFICATION AND SOURCES

PBCs are broadly categorized into phenolic compounds, terpenoids, polysaccharides, and OSCs. These compounds possess distinct structural characteristics and exhibit diverse biological activities, including antioxidant, anti-inflammatory, antimicrobial, immunomodulatory, and growth-promoting activities, positioning them as promising alternatives to conventional feed additives and antibiotics. In animal nutrition, they are supplied as feed additives either in the form of crude extracts or as individual compounds. Phenolic compounds represent a large and diverse group of plant-derived metabolites found abundantly in fruits, vegetables, cereals, legumes, and nuts [11]. The main phenolic compounds include phenolic acids, flavonoids, stilbenes, lignans, and tannins. Owing to their structural diversity, these compounds exhibit a wide-range of biological activities and contribute to improved animal health and performance [12]. Similarly, terpenoids represent the largest and most structurally diverse class of secondary metabolites. They are derivatives of terpenes, containing oxygen functional groups and are structurally composed of five-carbon (C5) entities called isoprene units [13]. These compounds are distinguished by their core carbon skeletons and associated functional groups. Accordingly, terpenoids are classified in to several types including monoterpenoids, sesquiterpenoids, diterpenoids, triterpenoids, and polyterpenoids. Medicinal and aromatic plants are major sources of these compounds, which are often found in essential oils (EOs) and contribute to improved nutrient absorption, as well as antimicrobial and antioxidant activities [14]. Alongside phenolics and terpenoids, polysaccharides are structurally diverse carbohydrates that perform various biological functions, serving as structural components, energy reserves, and dietary fibers.

Polysaccharides are recognized for their positive impact on animal health by modulating inflammation, metabolism, and oxidative stress [15]. Major plant-derived polysaccharides include starch (abundant in grains and roots), cellulose (the principal structural polymer in plant cell walls), and pectin (prevalent in fruits and vegetables). Owing to their biodegradability, biocompatibility, and modifiable functional properties, plant polysaccharides are widely used in the food, pharmaceutical, and livestock industries. In addition to these compounds, OSCs represent another important group of PBCs that are abundantly present in Allium species such as garlic, onions, and leeks, as well as in cruciferous vegetables including broccoli, cabbage, and cauliflower [16]. Representative OSCs, such as allicin and sulforaphane, contribute to the characteristic pungent aroma of these plants and exhibit potential therapeutic properties. These compounds possess various biological activities, including antioxidant and anti-inflammatory activities and have shown potential to improve the animal performance by modulating microbiota in pigs [17]. Similarly alkaloids and glycosides represent another important group of PBCs that exhibit diverse biological activities. However, their efficacy and safety as feed additives depend largely on their specific chemical structures and concentrations. Alkaloids are nitrogen-containing compounds biosynthesized from amino acid precursors, particularly lysine, phenylalanine, tyrosine, and tryptophan, and they typically contain one or more nitrogen atoms within a heterocyclic ring [18]. Glycosides are compounds in which a sugar moiety (glycone) is linked via a glycosidic bond to the anomeric carbon of a non-sugar moiety (aglycone) [19]. Certain alkaloids (i.e., sanguinarine, berberine, and capsaicin) and glycosides, (i.e, saponins) have been reported to improve growth performance and gut health by regulating the intestinal microbiota, reducing methane emissions and improving nutrient utilization in animals [20–23]. However, some alkaloids and glycosides may exert toxicological and anti-nutritional effects at elevated doses; therefore, their application must be carefully managed.

A BRIEF ACCOUNT ON MECHANISMS UNDERLYING THE EFFECTS OF PLANT-DERIVED BIOACTIVE COMPOUNDs

PBCs are administered via animal feed either as crude plant extracts or as isolated bioactive compounds, depending on formulation and intended function. They regulate the oxidative stress, inflammation, microbial, metabolic, and stress-response pathways to enhance health and performance in livestock and poultry animals (Figure 1). Phenolic compounds, including flavonoids, tannins, and phenolic acids, act as direct radical scavengers, induce endogenous antioxidant enzymes (i.e., superoxide dismutase [SOD] and glutathione peroxidase [GSH-Px]), reduce pro-inflammatory mediators (i.e., interleukin [IL]-6), and regulate oxidative stress- and inflammation-associated pathways, including activation of nuclear factor erythroid 2-related factor 2 (Nrf2) and inhibition of nuclear factor kappa B (NF-κB) signaling [24–26]. These activities assist to improve oxidative balance and decrease chronic inflammation, both of which are major causes of impaired metabolic efficiency and increased disease susceptibility in animals. Niu et al. [27] demonstrated that supplementation with plant essential oil (PEO) or coated plant essential oil (CEO) enhances growth performance in nursery piglets and mitigates LPS-induced hepatic oxidative stress via activation of the SIRT1–PGC-1α signaling axis. Notably, CEO exhibits a more pronounced antioxidant effect than PEO. Beyond their antioxidant and anti-inflammatory effects, PBCs also exert antimicrobial effects through multiple mechanisms, including disruption of bacterial membranes, damage to cell walls, inhibition of major enzymes (DNA gyrase and topoisomerase), suppression of biofilm formation, impairment of microbial metabolism, and prevention of pathogen colonization [28–31]. Alongside their established therapeutic effects, PBCs contribute to the maintenance of intestinal barrier integrity and support efficient nutrient transport within the gastrointestinal tract (GI). These effects are mediated through multiple mechanisms, including regulation of the mRNA expression of tight junction (TJ) proteins, cytokines, and chemokines, increased goblet cell numbers and mucin gene expression, and regulation of intestinal immune response [10]. Collectively, these processes reduce passive intestinal permeability and strengthen epithelial barrier function. Notably, the mechanisms underlying PBCs mediated enhancement of TJ integrity vary depending on the specific compound. In addition, PBCs exhibit prebiotic-like effects by reshaping the gut microbiota, promoting beneficial non-pathogenic bacteria while suppressing pathogenic species through complex microbial interactions, thereby contributing to overall gut health.

Figure 1

Mechanism underlying the beneficial effects of plant bioactive compounds. ROS, reactive oxygen species; SOD, superoxide dismutase; CAT, catalase; GSH-Px, glutathione peroxidase; TNF-α, tumor necrosis factor-alpha; IL-6, interleukin-6; IL-1β, interleukin-1 beta; NF-κB, nuclear factor kappa B; Nrf2, nuclear factor erythroid 2-related factor 2; CH₄, methane.

Mao et al. [32] reported that supplementation with quercetin alleviated weaning-associated diarrhea by regulating the NF-κB signaling pathway and controlling the balance between anti-inflammatory and pro-inflammatory factors. Additionally, quercetin reshaped the gut microbiota by reducing Proteobacteria and enhancing beneficial bacterial diversity, thereby improving intestinal homeostasis, nutrient absorption, feed efficiency, and overall growth performance in weaned piglets. Supplementation with PBCs and crude plant extracts has been shown to reduce methane emissions through multiple mechanisms. Methane production in ruminants is primarily driven by methanogenic archaea that use major fermentation end products as substrates. Dietary inclusion of PBCs has been reported to suppress members of the Methanobacteriaceae, a dominant methanogenic family thereby decreasing methane level. An important mechanism involves the inhibition of ruminal protozoa. Hydrogenosomes with in ruminal protozoa generate H₂, which serves as a primary substrate for methanogenesis through the hydrogenotrophic methanogenesis [33]. Consistently, a strong positive association among protozoa abundance and methane generation has been reported [34]. For instance, supplementation with mulberry leaf flavonoids (MLF) [35] reduced the number of protozoa population and consequently decreased methane production.

PLANT-DERIVED BIOACTIVE COMPOUND-DRIVEN EFFECTS IN FARM ANIMALS HEALTH AND PRODUCTION

Effects of plant-derived bioactive compound supplementation in poultry

Flavonoids have been associated with numerous biological benefits in poultry, including improved growth performance, anti-microbial activity, and enhanced antioxidant activity. Owing to their strong antioxidant properties, dietary flavonoids are widely explored as functional feed additives to promote poultry health and productivity. Supplementation with flavonoids such as genistein [36], hesperidin [36,37], quercetin [38], naringin [37], baicalin [24], and rutin [39] have enhanced total antioxidant capacity, thereby strengthening the endogenous defense system against oxidative damage. Among these compounds, genistein and hesperidin downregulate heat shock protein expression—a molecular marker of cellular stress [36]. In addition, hesperidin and naringin reduce malondialdehyde concentrations, a widely recognized indicator of lipid peroxidation [37]. Collectively, these effects contribute to the attenuation of oxidative stress, preservation of cellular integrity, and improved physiological performance in poultry. Quercetin act as a phytogenic feed additive in poultry, improving growth performance and meat quality through multiple mechanisms. These include inhibition of low-density lipoprotein oxidation, protection of erythrocytes from oxidative damage, and broad-spectrum antibacterial activity against Salmonella enterica serotype Typhimurium, Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa in broiler chickens [38,40].

Curcuminoids and lipophilic turmeric extracts, which contain bioactive constituents such as curcumin and turmerones, possess well-documented gastroprotective, antioxidant, and anti-inflammatory properties. These activities contribute to improved intestinal integrity and more efficient nutrient utilization in poultry. Dietary inclusion turmeric-derived compounds has therefore been associated with enhanced the growth performance in broiler chickens [41]. Consistently, Rajput et al. [42] reported that supplementation of broiler diets with curcumin for 42 days considerably increased body weight gain and feed efficiency during the finishing stage (22–42 days), although no considerable improvements were observed during the starting period (0–21 days). In addition to its growth-promoting effects, curcumin exhibits hepatoprotective properties by mitigating the toxic effects of aflatoxins, primarily through inhibition of cytochrome P450 isozymes in the liver [43]. Similarly, Sun et al. [44] demonstrated that dietary lycopene supplementation (0–80 mg kg⁻¹ feed) improved reproductive performance in laying hens by strengthening both hepatic and systemic antioxidant defenses. Lycopene increased the activities of SOD, T-AOC, glutathione peroxidase, and GSH/GSSG ratio, while simultaneously lowering serum cholesterol levels and increasing HDL-cholesterol and triiodothyroxine levels. These physiological changes, collectively improved oxidative stability and reproductive efficiency in hens. Dietary supplementation with Lycium barbarum flavonoids (500 mg/kg) has been shown to improve growth performance, intestinal barrier function, immune responses, and antioxidant capacity is ducks. These beneficial effects were associated with activation of the Nrf2 signaling pathway and inhibition of the of the NF-κB pathway, suggesting a regulatory role in oxidative stress and inflammatory responses [45]. Similarly, Hong et al. [46] reported that the inclusion of EO (125 ppm) derived from oregano, anise, and citrus peel in broiler diet improved overall performance. Birds receiving the supplemented diet exhibited approximately ~10% higher survival rates along with reduced serum cholesterol and very low density lipoprotein, indicating improved physiological status and metabolic health.

EO have also been reported to improve meat quality in poultry, producing more tender breast meat and juicier thigh muscles compared with unsupplemented controls. In addition, dietary inclusion of EO containing bioactive compounds in menthol, anethole, and eugenol has been associated with improved growth performance in broiler chickens [47]. Similar performance-enhancing effects have been documented for carvacrol administered either alone [48] or in combination with thymol [49]. Beneficial impacts on production traits have also been observed in laying hens supplemented with thymol and cinnamaldehyde [47] or with EO derived from Citrullus lunatus [50]. Beyond their growth promoting properties, EO and trans-cinnamaldehyde exhibit strong antimicrobial activity in poultry. Salmonella infection represents a major concern in the poultry industry; however, dietary cinnamaldehyde supplementation has been shown to effectively reduce bacterial colonization, limit horizontal transmission, and decrease egg contamination in both broiler and layer chickens [51].

Dietary supplementation with Astragalus polysaccharides (APSs) has been shown to enhance intestinal mucosal immunity in Newcastle disease–vaccinated chickens. APS administration increased the jejunal villus height-to-crypt depth ratio, elevated the IgA⁺ cell abundance, and enhanced secretory IgA levels, collectively indicating improved intestinal immune function. These findings suggest that APS can serve as an effective natural immunopotentiator and vaccine adjuvant in poultry [52]. Similarly, dietary inclusion of polysaccharides from Ginseng, APS, and Salvia miltiorrhiza reported to improve growth performance and immune competence in broiler chickens. These polysaccharides enhance serum immunoglobulin levels, regulate cytokine production, increase antioxidant enzyme activities, promote volatile fatty acids, and beneficially modulate the composition of the cecal microbiota [15]. Onion contains a range of bioactive compounds, particularly OSCs, which have been associated with several physiological benefits in poultry. Dietary supplementation with onion derived-OSCs has been reported to reduce blood glucose levels, potentially stimulating the central nervous system and increasing feed intake, thereby contributing to improved body-weight gain [53]. Inaddition, Jimoh et al. [54] observed that dietary garlic supplementation, across various inclusion levels, significantly decreased the caecal population of Clostridium perfringens compared with the control group, an effect attributed to its OSC content. Isoquinoline alkaloids have also demonstrated beneficial effects in broiler production systems. These compounds effectively alleviated stress induced by high stocking density, improving growth performance, immune responses, and intestinal health. Dietary supplementation with isoquinoline alkaloids derived from Macleaya cordata (0.6 mg/kg) alleviated lipopolysaccharide-induced liver injury by enhancing immune function and suppressing hepatic inflammation through modulation of the TLR4/MyD88/NF-κB signaling pathway [55]. Similary, supplementation with isoquinoline alkaloids and flavonoids, alone or in combination, alleviated heat and density stress in broilers by improving growth, gut morphology, and anti-inflammatory responses. Their combined application showed synergistic effects by improving microbiota diversity and metabolic pathways, demonstrating potential as effective feed additives under challenging rearing conditions [56]. The effects of the various PBCs in poultry are presented in Table 1.

Table 1

The major biological effects of plant bioactive compounds in poultry

Effects of plant-derived bioactive compound supplementation in livestock animals

Ruminants: Dietary supplementation with quercetin in beef cattle has shown limited effects on meat quality and antioxidant activity. Although inclusion of 42 ppm quercetin increased loin pH and cohesiveness, no significant improvements were observed in antioxidant capacity, lipid oxidation, or other physicochemical characteristics. These findings suggest that a low inclusion level of quercetin (10%) may be insufficient to produce measurable biochemical benefits in beef production systems [57]. In vitro investigations have demonstrated that flavonoids such as naringin and quercetin, when supplemented at 4.5% of substrate, dry matter, effectively suppressed methane production without negatively affecting rumen fermentation efficiency. While, other flavonoids, including flavone, myricetin, catechin, rutin, and kaempferol, were found to reduce dry matter degradability, enzyme activities, and microbial growth [58]. Supplementation with MLF and resveratrol has also been reported to improve nutrient digestibility and reduced methane emissions in sheep. Both polyphenols enhanced energy utilization and decreased CH₄ and CO₂ production, with resveratrol showing comparatively stronger mitigation effects. However, neither treatment improved nitrogen retention, indicating selective benefits related to methane mitigation and feed efficiency [59]. Consistent with these findings, Ma et al. [35] reported that supplementation improved nutrient digestibility and modulated rumen microbial population in sheep. Flavonoids increased nitrogen and fiber digestibility, elevated total volatile fatty acids, and reduced methane emissions by suppressing protozoa and methanogen while promoting the abundance of Fibrobacter succinogenes, thereby enhancing rumen efficiency and decreasing methanogenesis.

Dietary supplementation with flavonoids derived from Allium mongolicum Regel has been shown to improve growth performance and regulate neuroendocrine function in meat sheep. Inclusion levels ranging from 11–33 mg/kg increased average daily gain and feed intake, while reducing the feed conversion ratio. These responses were accompanied by elevated serum concentrations of GH and IGF-1 levels, along with decreased corticosterone, indicating improved growth efficiency and enhanced stress resilience through endocrine regulation [60]. Similarly, flavonoids extracted from Citrus aurantium have been reported to influence feeding behavior and rumen health in Holstein bulls. Although no significant changes in overall growth performance was observed, animals receiving flavonoid supplementation exhibited smaller meal sizes, reduced agonistic and sexual behaviors, and healthier rumen walls. These findings suggest that citrus-derived flavonoids may enhance animal welfare and gastrointestinal resilience in cattle [61]. Dietary supplementation with citrus flavonoids, particularly hesperidin and naringin, has been reported to enhance milk oxidative stability of milk in dairy ewes without affecting milk yield, composition, or fatty acid profile. These bio active compounds reduced milk malondialdehyde levels, indicating improved antioxidant protection and enhanced resistance to oxidative deterioration, while maintaing milk quality or coagulation properties [62]. Citrus flavonoids also exhibit synergistic potential in regulating rumen fermentation. In vitro studies have shown that naringin and hesperidin, either supplemented together or as part of a mixed citrus flavonoid extract (CFE), more effectively inhibited ruminal methanogenesis and ammoniagenesis. This effect was associated with suppression of methanogenic archaea (Methanobrevibacter) and rumen protozoa (Isotricha, Entodinium), thereby improving nitrogen utilization and reducing enteric methane (CH₄) emissions in dairy cows [63].

More recently, Hao et al. [64] reported that sea-buckthorn flavonoids improved growth performance, nutrient digestibility, and antioxidant status in finishing lambs. Moderate inclusion level enhanced rumen fermentation, stimulated microbial protein synthesis, and improved nitrogen utilization, while simultaneously reducing oxidative stress markers. These results suggest that sea-buckthorn flavonoids can enhance metabolic efficiency and oxidative resilience in ruminant production systems. Twelve Liuyang black goats were assigned to control or 2% tannic acid diets in a two-stage experiment for 20 days. Tannic acid significantly reduced methane emissions and fiber intake (p<0.05). Microbial shifts included increased Firmicutes and reduced Methanobrevibacter and Prevotella. Rumen fermentation was altered, with increased valerate and butyrate and a reduced acetate-to-propionate ratio. These findings suggest tannic acid mitigates methane production by modulating rumen microbial composition and fermentation [65]. Similarly, dietary inclusion of tea saponins in Dorper× Thin-tailed Han ewes improved rumen fermentation characteristics, nutrient utilization, and methane mitigation. Saponin supplementation enhanced the digestibility of organic matter, nitrogen, neutral detergent fiber, and acid detergent fiber, while increasing nitrogen retention and reducing methane emissions by 8.8%. Additionally, it elevated the proportion of propionate and the abundance of Fibrobacter succinogenes, while decreasing ruminal ammonia concentration’s and protozoa populations, indicating improved rumen efficiency and reduced methanogenesis [66]. Yang et al. [67] reported that dietary supplementation of garlic EO (5 g/day) in the diets of lactating cows tended to enhance milk fat content (p<0.10) without significantly affecting dry matter intake or ruminal fiber digestibility. Similarly, Hundal et al. [68] evaluated several EOs, including cinnamaldehyde, carvacrol, limonene, and carvone to determine their efficacy in mitigating enteric methane emissions while maintaining nutrient digestibility. Although supplementation levels exceeding 1% of carvacrol or limonene effectively reduced methane production, these higher inclusion rates were also associated with a decline in overall nutrient digestibility.

In another study, dietary supplementation with orange peel EO (up to 300 mg/kg concentrate) to lactating Chios ewes improved milk yield as well as fat and ash production, while reducing the proportion of milk unsaturated fatty acids and the atherogenic index in milk. However, increasing the supplementation level to 450 mg/kg did not further enhance milk yield, although it improved antioxidant status in both plasma and milk [69]. Rapeseed oil contain sterols and phenolic acids, and its dietary inclusion of rapeseed oil at 41 g/kg of dry matter in the lactating dairy cows diets has been shown to reduce daily methane emissions by approximately 22.5%. This reduction was associated with shifts in rumen microbial composition, including increased abundance of Methanosphaera and members of the Succinivibrionaceae family, along with a decrease in Bifidobacteriaceae populations [70]. Similarly, supplementation with Zanthoxylum bungeanum EO influenced the composition of the small-intestinal microbiota in sheep. The treatment altered the relative abundance of key bacterial genera, including Prevotella, Ruminococcus, and Christensenellaceae, which are closely associated with nutrient digestion and intestinal health [71]. In another study, administration of oregano essential oil (OEO) at a dosage of 300 mg/kg enhanced the growth rate of Sewa sheep. The enhancement in growth was associated with improved intestinal morphology and beneficial modulation of gut microbiota composition. Specifically, OEO supplementation significantly increased average daily gain, slaughter rate, small intestinal villus length, and the abundance of beneficial gut bacteria [72]. Similarly, supplementation with Lippia graveolens EO in lambs did not significantly influence growth performance, rumen fermentation traits, or carcass yield. However, it enhanced meat antioxidant activity, improved crude protein stability, and extended meat shelf life, indicating improved meat quality without negatively affecting productive performance [73]. Also, Ritt et al. [74] investigated the effects of OEO supplementation (60 mg kg⁻¹ body weight day⁻¹) in pre-weaned Holstein calves. The supplementation increased starter feed intake and enhanced microbial diversity in both the rumen and jejunum. In addition, OEO reduced the abundance of potentially pathogenic genera, including Streptococcus, Escherichia, and Clostridium, indicating improved microbial balance within the GI. However, no significant effects were observed on overall growth performance or rumen fermentation parameters, suggesting that OEO primarily modulates gut microbiota and feed intake without markedly altering physiological growth responses.

APS is a predominant water-soluble heteropolysaccharide derived from the roots of Astragalus membranaceus. It mainly consists of monosaccharides such as glucose, arabinose, and galactose interconnected through glycosidic linkages. Dietary supplementation with APS has been reported to improve rumen fermentation characteristics and antioxidant status in weaned lambs. Supplementation enhanced growth performance, propionate production, increased antioxidant enzyme activities, and stimulated immune responses, while reducing plasma cortisol levels [75]. Supplementation enhanced growth performance and immune responses while improving rumen microbial composition in yaks, with increased abundance of Methanobrevibacter and Butyrivibrio, microbes involved in fiber degradation and immune regulation [76]. Also, it improved growth performance, rumen function, metabolic efficiency, and serum antioxidant capacity in Angus bulls [77]. Alfalfa and sea weed polysaccharides supplementation significantly reduced diarrhea in calves, with reductions of 18.12% and 30.9%, respectively. These effects were linked to modulation of gut microbiota, characterized by increased beneficial bacteria and decreased pathogens, along with regulation of immune and inflammatory pathways. Sea weed polysaccharides exhibited greater efficacy than Alfalfa polysaccharides in alleviating intestinal inflammation [78]. Garlic powder rich in OSCs has been shown to reduce enteric methane emissions and enhanced milk yield in lactating Murrah buffaloes without affecting nutrient digestibility or milk composition. Supplementation at 2% DMI lowered methane output by up to 31%, indicating garlic derived OSCs as natural feed additives for improving rumen efficiency and promoting sustainable milk production [79]. A summary of the diverse effects of PBCs in ruminant animals is presented in Table 2.

Table 2

The major biological effects of plant bioactive compounds in ruminant animals

Pigs: Piglets fed diets enriched with polyphenol-rich extracts, such as grape or hop, exhibited reduced expression of inflammation-associated genes in the duodenum, ileum, and colon accompanied by a decreased abundance of Clostridium in the fecal microbiota [80]. Similarly, supplementation with polyphenol-rich seed and pomace extracts downregulated NF-κB signaling in the duodenal mucosa, indicating suppression of intestinal inflammatory responses [81]. In another study, piglets challenged with E. coli and fed commercial polyphenol-rich diets showed a reduced incidence of diarrhea, further confirming the intestinal anti-inflammatory potential of polyphenols [82]. In LPS-challenged piglets, dietary inclusion of soy isoflavones strengthen immune function while reducing diarrhea and circulating endotoxin levels [83]. Moreover, resveratrol supplementation effectively alleviated intestinal inflammation and oxidative stress induced by deoxynivalenol exposure, while improving microbial balance and intestinal barrier integrity in piglets [84]. Dietary supplementation with quercetin has been shown to enhance growth and immune function in growing pigs challenged with LPS. Specifically, quercetin improved average daily gain and nutrient digestibility, while modulating immune responses by decreasing the pro-inflammatory cytokine IL-6 and increasing immunological indicators such as IgG, white blood cell counts, and lymphocyte levels. These responses suggest that quercetin exerts immunomodulatory and growth-promoting effects under inflammatory conditions [25].

Seven days supplementation with puerarin markedly enhanced the intestinal antioxidant defense system in 18-day-old piglets challenged with porcine epidemic diarrhea virus. This improvement was evidenced by increased activities of antioxidant enzymes, including SOD and GSH-Px in the duodenum and colon. In addition, puerarin administration reduced the concentrations of oxidative stress indicators such as H₂O₂ and MDA levels in the ileum, indicating a protective effect against virus-induced oxidative damage in the intestinal tissues [26]. Recent studies have demonstrated that MFL enhanced growth performance, carcass traits, and antioxidant capacity in pigs. Dietary supplementation with MFL has been shown to improve the growth performance and meat quality, particularly by enhancing meat tenderness. Furthermore, MFL supplementation has been reported to reduce fat synthesis and favorably alter fatty acid profiles in adipose tissue, indicating its potential to improve lipid metabolism and overall meat quality in pigs [85,86]. Citrus flavonoids supplementation promoted piglet growth and intestinal health by regulating the TLR2/NF-κB signaling pathway. It improved gut microbial balance by increasing the relative abundance of Bacteroidetes and Prevotella, while reducing Tenericutes and Clostridiales, indicating a shift toward a more beneficial intestinal microbial community. An inclusion level of 80 mg/kg was identified as the most effective dose for improving piglet’s performance [87]. Gan et al. [88] demonstrated that dietary curcumin supplementation reduced the intestinal abundance of pathogenic E. coli in weaned piglets. This treatment also suppressed the TLR4 signaling pathway, modulated IL expression, and increased immunoglobulin levels, indicating improved intestinal immune responses. Similarly, Zhang et al. [89] reported that curcumin act as a natural antioxidant and can be incorporated into dietary strategies to alleviate oxidative stress in IUGR offspring, thereby improving redox status in leg muscle and meat quality. In addition, curcumin supplementation has been shown to attenuate oxidative damage and protect the structural integrity of jejunal cell organelles and membranes in piglets [90]. Brus et al. [91] reported that supplementation with a mixture of chestnut wood tannins and organic acids reduced harmful E. coli populations while increasing beneficial lactic acid bacteria in piglets during an 82–127 day feeding period. Similarly, dietary inclusion of EOs containing cinnamaldehyde (15%) and thymol (5%) combined with organic acids, improved growth performance, resulting in approximately 13.5% higher average daily gain and 5.6% greater final body weight in weaned piglets [92]. EO rich in thymol and cinnamaldehyde were also shown to reduce IL-6 production, enhance lymphocyte proliferation, and increase plasma IgA and IgM levels in weaning pigs. Moreover, EO containing cinnamaldehyde, thymol, and carvacrol reduced fecal nitrogen and ammonia emissions by suppressing microbial protease and urease activities [93,94]. Additionally, supplementation with 2,000 mg/kg EO coated with glycerol monolaurate in weanling piglets enhanced serum antioxidant capacity and immune status, modulates jejunal inflammatory cytokines and intestinal morphology, and thereby promotes improved growth performance [95].

Artuso-Ponte et al. [96] reported that supplementation with quaternary benzo[c]phenanthridine alkaloids derived from herbal extracts alleviated transportation stress in pigs and positively influenced pork safety. Achyranthes bidentata polysaccharide supplementation improved physiological functions in weaned piglets. A higher dose (1,600 mg/kg) increased serum phosphorus and supported hepatic health, whereas a lower dose (800 mg/kg) elevated iron and immunoglobulins. Both doses enhanced antioxidant capacity and improved lipid metabolism by reducing triglyceride and LDL cholesterol [97]. The combined supplementation of boric acid and plant polysaccharides synergistically enhanced growth performance and immune function in fattening pigs by increasing intestinal enzyme activity, antioxidant capacity, and nutrient absorption, while reducing emissions of harmful gas and heavy metals [98]. Moreover, Achyranthes bidentate polysaccharide, and glycyrrhiza polysaccharides have been shown to counteract porcine reproductive and respiratory syndrome virus infection [99,100]. Similarly, APS inhibits the proliferation of porcine circovirus type 2 and mitigates associated tissue damage [28]. A summary of the diverse biological effects of PBCs in non-ruminant animals is presented in Table 3.

Table 3

The major biological effects of plant bioactive compounds in pigs

CONCLUSION AND AREAS OF FUTURE RESEARCH

PBCs influence livestock health and performance through diverse physiological and metabolic processes. Their effects depend on factors including botanical origin, chemical composition, bioavailability, dosage, and host interactions, while variability in composition complicates evaluation of efficacy and delivery strategies. Antioxidant, anti-inflammatory, antimicrobial, immunomodulatory, and microbiota-regulatory activities have been widely reported for PBCs; however, the underlying molecular mechanisms governing these effects remain incompletely understood. Therefore, future studies should prioritize mechanistic characterization and integrated omics approaches to clarify the molecular mechanisms governing PBCs activities. Beyond evaluating biological activities of PBCs, research should also consider economic feasibility, environmental impacts, and practical implementation in livestock and poultry systems. Assessing production costs, resource efficiency, and scalability of PBC-based feed additives will be essential to ensure that these strategies contribute to environmentally responsible and economically sustainable animal production.

Although most studies report beneficial effects, certain PBCs may produce adverse effects under specific conditions. These adverse effects are often dose-dependent, as excessive inclusion levels can impair feed intake, reduce nutrient digestibility, and disrupt normal organ function, showing the importance of carefully determining optimal dosage levels for safe and effective application in livestock and poultry nutrition. For instance, compounds that confer antioxidant and antimicrobial may also exhibit antinutritional properties at high concentrations by binding dietary proteins and reducing feed palatability. In addition, elevated levels of some PBCs have been reported to impair sperm function in reproductive contexts. Therefore, careful evaluation of the safety, dosage, and conditions of use of PBC-based feed additives is essential when assessing their suitability for animal production. Furthermore, establishing comprehensive and standardized evaluation system is essential for the reliable assessment of PBCs in livestock production. Moreover, many PBCs exhibit limited stability and are rapidly degraded in the GI, restricting their bioavailability and functional efficacy. To address this limitation, advanced delivery systems—including micro- and nanoencapsulation and lipid-based carriers—have been developed to enhance stability and enable targeted release. However, their large-scale application in animal feed remains constrained by challenges related to cost, scalability, and regulatory approval. Overcoming these barriers will require standardized formulations and coordinated efforts among researchers, industry, and regulatory agencies.

Plant based feeds have long been used in traditional animal farming practices on various forms; however, only in recent years has research intensified to elucidate biosynthesis, distribution, chemistry, and mechanisms of action of PBCs in animals. The integration of PBCs into livestock production offers a promising opportunity to develop sustainable, cost-effective, and environmentally friendly alternatives to conventional antibiotics. However, recognizing PBCs potential requires further research to evaluate their safety, efficacy, and consistency prior to large-scale implementation in commercial production systems.

Notes

CONFLICT OF INTEREST

No potential conflict of interest relevant to this article was reported.

AUTHORS’ CONTRIBUTION

Conceptualization: Tuong DTC, Karthikeyan A.

Writing - original draft: Tuong DTC, Karthikeyan A.

Writing - review & editing: Tuong DTC, Karthikeyan A, Min LLL, Anjana S, Funaba M, Roh S, Min T.

FUNDING

This work was supported by the 2025 National University Development Project grant of Jeju National University funded by the Ministry of Education and the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (2022R1A2B5B02001711 and RS-2025-25459210).

ACKNOWLEDGMENTS

Not applicable.

SUPPLEMENTARY MATERIAL

Not applicable.

DATA AVAILABILITY

Upon reasonable request, the datasets of this study can be available from the corresponding author.

ETHICS APPROVAL

Not applicable.

DECLARATION OF GENERATIVE AI

During the preparation of this work the author(s) used Grammarly and ChatGpt to improve the language. After using this tool/service, the author(s) reviewed and edited the content as needed and take(s) full responsibility for the content of the publication.

References

1. Wang L, Li D. Current status, challenges and prospects for pig production in Asia. Anim Biosci 2024;37:742–54. https://doi.org/10.5713/ab.23.0303.

2. Senawin S, Bunchasak C, Rakangthong C, et al. Microbiota profiles and antimicrobial resistance genes in sow fecal samples from farms with and without antibiotic use. Anim Biosci 2025;38:2487–98. https://doi.org/10.5713/ab.25.0062.

3. Wongtangtintharn S, Chakkhambang S, Pootthachaya P, Cherdthong A, Wanapat M. Challenges and constraints to the sustainability of poultry farming in Thailand. Anim Biosci 2025;38:845–62. https://doi.org/10.5713/ab.24.0685.

4. Yoon I, Jung JH, Oh SH, Kim SW. Policy recommendations for sustainable livestock farming in South Korea. Anim Biosci 2025;38:2297–311. https://doi.org/10.5713/ab.25.0307.

5. European Union. Regulation (EC) No 470/2009 of the European Parliament and of the Council of 6 May 2009: laying down community procedures for the establishment of residue limits of pharmacologically active substances in foodstuffs of animal origin, repealing Council Regulation (EEC) No 2377/90 and amending Directive 2001/82/EC of the European Parliament and of the Council and Regulation (EC) No 726/2004 of the European Parliament and of the Council (text with EEA relevance) European Union; 2009.

6. Greathead H. Plants and plant extracts for improving animal productivity. Proc Nutr Soc 2003;62:279–90. https://doi.org/10.1079/PNS2002197.

7. Acamovic T, Brooker JD. Biochemistry of plant secondary metabolites and their effects in animals. Proc Nutr Soc 2005;64:403–12. https://doi.org/10.1079/pns2005449.

8. Mitropoulou G, Stavropoulou E, Vaou N, et al. Insights into antimicrobial and anti-inflammatory applications of plant bioactive compounds. Microorganisms 2023;11:1156. https://doi.org/10.3390/microorganisms11051156.

9. Singh AK, Ojha L, Kumari P, Choubey M, Chaudhary SK. Phytochemicals as natural feed additives for ruminants. In : Mahesh MS, Yata VK, eds. Feed additives and supplements for ruminants Springer Nature; 2024. p. 167–96.

10. Patra AK, Amasheh S, Aschenbach JR. Modulation of gastrointestinal barrier and nutrient transport function in farm animals by natural plant bioactive compounds: a comprehensive review. Crit Rev Food Sci Nutr 2019;59:3237–66. https://doi.org/10.1080/10408398.2018.1486284.

11. Bento C, Gonçalves AC, Jesus F, Simões M, Silva LR. Phenolic compounds: sources, properties and applications. In : Porter R, Parker N, eds. Bioactive compounds: sources, properties and applications Nova Science Publishers; 2017. p. 271–99.

12. Mahfuz S, Shang Q, Piao X. Phenolic compounds as natural feed additives in poultry and swine diets: a review. J Anim Sci Biotechnol 2021;12:48. https://doi.org/10.1186/s40104-021-00565-3.

13. Ashour M, Wink M, Gershenzon J. Biochemistry of terpenoids: monoterpenes, sesquiterpenes and diterpenes. In : Wink M, ed. Annual plant reviews 40: biochemistry of plant secondary metabolism Blackwell; 2010. p. 258–303.

14. Camara JS, Perestrelo R, Ferreira R, Berenguer CV, Pereira JAM, Castilho PC. Plant-derived terpenoids: a plethora of bioactive compounds with several health functions and industrial applications: a comprehensive overview. Molecules 2024;29:3861. https://doi.org/10.3390/molecules29163861.

15. Zhao G, Niu Y, Wang H, et al. Effects of three different plant-derived polysaccharides on growth performance, immunity, antioxidant function, and cecal microbiota of broilers. J Sci Food Agric 2024;104:1020–9. https://doi.org/10.1002/jsfa.12988.

16. Ramirez DA, Locatelli DA, González RE, Cavagnaro PF, Camargo AB. Analytical methods for bioactive sulfur compounds in allium: an integrated review and future directions. J Food Compos Anal 2017;61:4–19. https://doi.org/10.1016/j.jfca.2016.09.012.

17. Sánchez CJ, Martínez-Miró S, Ariza JJ, et al. Effect of Alliaceae extract supplementation on performance and intestinal microbiota of growing-finishing pig. Animals 2020;10:1557. https://doi.org/10.3390/ani10091557.

18. Bhambhani S, Kondhare KR, Giri AP. Diversity in chemical structures and biological properties of plant alkaloids. Molecules 2021;26:3374. https://doi.org/10.3390/molecules26113374.

19. Khan H, Amin S, Patel S. Targeting BDNF modulation by plant glycosides as a novel therapeutic strategy in the treatment of depression. Life Sci 2018;196:18–27. https://doi.org/10.1016/j.lfs.2018.01.013.

20. Kantas D, Papatsiros VG, Tassis PD, Athanasiou LV, Tzika ED. The effect of a natural feed additive (Macleaya cordata), containing sanguinarine, on the performance and health status of weaning pigs. Anim Sci J 2015;86:92–8. https://doi.org/10.1111/asj.12240.

21. Ridla M, Laconi EB, Nahrowi , Jayanegara A. Effects of saponin on enteric methane emission and nutrient digestibility of ruminants: an in vivo meta-analysis. IOP Conf Ser Earth Environ Sci 2021;788:012028. https://doi.org/10.1088/1755-1315/788/1/012028.

22. Namted S, Poungpong K, Bunchasak C. Effects of dietary capsaicin supplementation on growth performance, blood profile and carcass and meat quality of finishing pigs. Anim Biosci 2024;37:1953–61. https://doi.org/10.5713/ab.23.0541.

23. Radin T, Bashtani M, Afshin M, Vargas-Bello-Pérez E, Ghavipanje N. Dietary berberine supplementation improves growth performance, liver-related blood parameters, and antioxidative status of fattening lambs. Anim Feed Sci Technol 2025;328:116443. https://doi.org/10.1016/j.anifeedsci.2025.116443.

24. Ishfaq M, Chen C, Bao J, et al. Baicalin ameliorates oxidative stress and apoptosis by restoring mitochondrial dynamics in the spleen of chickens via the opposite modulation of NF-κB and Nrf2/HO-1 signaling pathway during Mycoplasma gallisepticum infection. Poult Sci 2019;98:6296–310. https://doi.org/10.3382/ps/pez406.

25. Park JH, Sureshkumar S, Kim IH. Influences of dietary flavonoid (quercetin) supplementation on growth performance and immune response of growing pigs challenged with Escherichia coli lipopolysaccharide. J Anim Sci Technol 2020;62:605–13. https://doi.org/10.5187/jast.2020.62.5.605.

26. Wu M, Yi D, Zhang Q, et al. Puerarin enhances intestinal function in piglets infected with porcine epidemic diarrhea virus. Sci Rep 2021;11:6552. https://doi.org/10.1038/s41598-021-85880-5.

27. Niu Y, Song X, Chen Y, et al. Plant essential oil supplementation promotes growth and attenuates lipopolysaccharide (LPS)-induced acute liver injury through SIRT1/PGC-1α signaling pathway in nursery pigs. Anim Biosci 2025;38:2464–74. https://doi.org/10.5713/ab.25.0066.

28. Xue H, Gan F, Qian G, et al. Astragalus polysaccharides attenuate PCV2 infection by inhibiting endoplasmic reticulum stress in vivo and in vitro. Sci Rep 2017;7:40440. https://doi.org/10.1038/srep40440.

29. Nguyen TLA, Bhattacharya D. Antimicrobial activity of quercetin: an approach to its mechanistic principle. Molecules 2022;27:2494. https://doi.org/10.3390/molecules27082494.

30. Pérez-Flores JG, García-Curiel L, Pérez-Escalante E, et al. Plant antimicrobial compounds and their mechanisms of action on spoilage and pathogenic bacteria: a bibliometric study and literature review. Appl Sci 2025;15:3516. https://doi.org/10.3390/app15073516.

31. Liu Y, Zhu J, Liu Z, Zhi Y, Mei C, Wang H. Flavonoids as promising natural compounds for combating bacterial infections. Int J Mol Sci 2025;26:2455. https://doi.org/10.3390/ijms26062455.

32. Mao Y, Yang Q, Liu J, et al. Quercetin increases growth performance and decreases incidence of diarrhea and mechanism of action in weaned piglets. Oxid Med Cell Longev 20242024;:5632260. https://doi.org/10.1155/2024/5632260.

33. Belanche A, de la Fuente G, Newbold CJ. Study of methanogen communities associated with different rumen protozoal populations. FEMS Microbiol Ecol 2014;90:663–77. https://doi.org/10.1111/1574-6941.12423.

34. Hassan F, Arshad MA, Ebeid HM, et al. Phytogenic additives can modulate rumen microbiome to mediate fermentation kinetics and methanogenesis through exploiting diet–microbe interaction. Front Vet Sci 2020;7:575801. https://doi.org/10.3389/fvets.2020.575801.

35. Ma T, Chen DD, Tu Y, Zhang NF, Si BW, Diao QY. Dietary supplementation with mulberry leaf flavonoids inhibits methanogenesis in sheep. Anim Sci J 2017;88:72–8. https://doi.org/10.1111/asj.12556.

36. Kamboh AA, Hang SQ, Bakhetgul M, Zhu WY. Effects of genistein and hesperidin on biomarkers of heat stress in broilers under persistent summer stress. Poult Sci 2013;92:2411–8. https://doi.org/10.3382/ps.2012-02960.

37. Goliomytis M, Kartsonas N, Charismiadou MA, Symeon GK, Simitzis PE, Deligeorgis SG. Influence of naringin or hesperidin dietary supplementation on broiler meat quality and oxidative stability. PLOS ONE 2015;10e0141652. https://doi.org/10.1371/journal.pone.0141652.

38. Goliomytis M, Tsoureki D, Simitzis PE, Charismiadou MA, Hager-Theodorides AL, Deligeorgis SG. Effects of quercetin dietary supplementation on broiler growth performance, meat quality, and oxidative stability. Poult Sci 2014;93:1957–62. https://doi.org/10.3382/ps.2013-03585.

39. Zhan J, Gu Z, Wang H, Liu Y, Wu Y, Huo J. Rutin alleviated lipopolysaccharide-induced damage in goat rumen epithelial cells. Anim Biosci 2024;37:303–14. https://doi.org/10.5713/ab.23.0028.

40. Iqbal Y, Cottrell JJ, Suleria HAR, Dunshea FR. Gut microbiota-polyphenol interactions in chicken: a review. Animals 2020;10:1391. https://doi.org/10.3390/ani10081391.

41. Johannah NM, Joseph A, Maliakel B, Krishnakumar IM. Dietary addition of a standardized extract of turmeric (TurmaFEEDTM) improves growth performance and carcass quality of broilers. J Anim Sci Technol 2018;60:8. https://doi.org/10.1186/s40781-018-0167-7.

42. Rajput N, Muhammad N, Yan R, Zhong X, Wang T. Effect of dietary supplementation of curcumin on growth performance, intestinal morphology and nutrients utilization of broiler chicks. J Poult Sci 2013;50:44–52. https://doi.org/10.2141/jpsa.0120065.

43. Zhang NY, Qi M, Zhao L, et al. Curcumin prevents aflatoxin B1 hepatoxicity by inhibition of cytochrome P450 isozymes in chick liver. Toxins 2016;8:327. https://doi.org/10.3390/toxins8110327.

44. Sun B, Ma J, Zhang J, Su L, Xie Q, Bi Y. Lycopene regulates production performance, antioxidant capacity, and biochemical parameters in breeding hens. Czech J Anim Sci 2014;59:471–9. https://doi.org/10.17221/7710-CJAS.

45. Tu M, Cai G, Ma L, et al. Effects of different levels of Lycium barbarum flavonoids on growth performance, immunity, intestinal barrier and antioxidant capacity of meat ducks. Antioxidants 2025;14:67. https://doi.org/10.3390/antiox14010067.

46. Hong JC, Steiner T, Aufy A, Lien TF. Effects of supplemental essential oil on growth performance, lipid metabolites and immunity, intestinal characteristics, microbiota and carcass traits in broilers. Livest Sci 2012;144:253–62. https://doi.org/10.1016/j.livsci.2011.12.008.

47. Paraskeuas V, Fegeros K, Palamidi I, Hunger C, Mountzouris KC. Growth performance, nutrient digestibility, antioxidant capacity, blood biochemical biomarkers and cytokines expression in broiler chickens fed different phytogenic levels. Anim Nutr 2017;3:114–20. https://doi.org/10.1016/j.aninu.2017.01.005.

48. Liu SD, Song MH, Yun W, et al. Effects of oral administration of different dosages of carvacrol essential oils on intestinal barrier function in broilers. J Anim Physiol Anim Nutr 2018;102:1257–65. https://doi.org/10.1111/jpn.12944.

49. Reis JH, Gebert RR, Barreta M, et al. Effects of phytogenic feed additive based on thymol, carvacrol and cinnamic aldehyde on body weight, blood parameters and environmental bacteria in broilers chickens. Microb Pathog 2018;125:168–76. https://doi.org/10.1016/j.micpath.2018.09.015.

50. Marume U, Mokagane JM, Shole CO, Hugo A. Citrullus lanatus essential oils inclusion in diets elicit nutraceutical effects on egg production, egg quality, and physiological characteristics in layer hens. Poult Sci 2020;99:3038–46. https://doi.org/10.1016/j.psj.2020.01.029.

51. Upadhyaya I, Upadhyay A, Kollanoor-Johny A, et al. In-feed supplementation of trans-cinnamaldehyde reduces layer-chicken egg-borne transmission of Salmonella enterica serovar enteritidis. Appl Environ Microbiol 2015;81:2985–94. https://doi.org/10.1128/AEM.03809-14.

52. Shan C, Sun B, Dalloul RA, et al. Effect of the oral administration of astragalus polysaccharides on jejunum mucosal immunity in chickens vaccinated against Newcastle disease. Microb Pathog 2019;135:103621. https://doi.org/10.1016/j.micpath.2019.103621.

53. Farahani M, Goodarzi M, Nanekarani S. The effects of aqueous extract of onion on performance and some blood biochemical parameters of the Cobb and Ross broilers. Int J Adv Biol Biomed Res 2015;3:370–7. https://doi.org/10.18869/IJABBR.2015.370.

54. Jimoh AA, Ibitoye EB, Dabai YU, Garba S. In vivo antimicrobial potentials of garlic against Clostridium perfringens and its promotant effects on performance of broiler chickens. Pak J Biol Sci 2013;16:1978–84. https://doi.org/10.3923/pjbs.2013.1978.1984.

55. Chen J, Yang W, Liu H, Niu J, Liu Y, Cheng Q. Protective effect of Macleaya cordata isoquinoline alkaloids on lipopolysaccharide-induced liver injury in broilers. Anim Biosci 2024;37:131–41. https://doi.org/10.5713/ab.23.0267.

56. Insawake K, Songserm T, Songserm O, et al. Flavonoids, isoquinoline alkaloids, and their combinations affect growth performance, inflammatory status, and gut microbiome of broilers under high stocking density and heat stress. Animals 2025;15:71. https://doi.org/10.3390/ani15010071.

57. Kang MG, Kim HJ, Jang AR, Gam DK, Yun GS, Jo CR. Effect of dietary supplementation of quercetin on antioxidant activity and meat quality of beef cattle. Korean J Agric Sci 2012;39:61–8. https://doi.org/10.7744/cnujas.2012.39.1.061.

58. Oskoueian E, Abdullah N, Oskoueian A. Effects of flavonoids on rumen fermentation activity, methane production, and microbial population. BioMed Res Int 20132013;:349129. https://doi.org/10.1155/2013/349129.

59. Chen D, Chen X, Tu Y, et al. Effects of mulberry leaf flavonoid and resveratrol on methane emission and nutrient digestion in sheep. Anim Nutr 2015;1:362–7. https://doi.org/10.1016/j.aninu.2015.12.008.

60. Muqier , Qi S, Wang T, Chen R, Wang C, Ao C. Effects of flavonoids from Allium mongolicum Regel on growth performance and growth-related hormones in meat sheep. Anim Nutr 2017;3:33–8. https://doi.org/10.1016/j.aninu.2017.01.003.

61. Paniagua M, Crespo J, Bach A, Devant M. Effects of flavonoids extracted from Citrus aurantium on performance, eating and animal behavior, rumen health, and carcass quality in Holstein bulls fed high-concentrate diets. Anim Feed Sci Technol 2018;246:114–26. https://doi.org/10.1016/j.anifeedsci.2018.08.010.

62. Simitzis P, Massouras T, Goliomytis M, et al. The effects of hesperidin or naringin dietary supplementation on the milk properties of dairy ewes. J Sci Food Agric 2019;99:6515–21. https://doi.org/10.1002/jsfa.9931.

63. Yu S, Zhao Y, Li L, Zhao H, Liu M, Jiang L. Flavonoids from citrus peel display potential synergistic effects on inhibiting rumen methanogenesis and ammoniagenesis: a microbiome perspective. Environ Sci Pollut Res 2024;31:21208–23. https://doi.org/10.1007/s11356-024-32509-5.

64. Hao X, Zhang X, Yang D, Xie Y, Mu C, Zhang J. Effects of sea-buckthorn flavonoids on growth performance, nutrient digestibility, microbial protein synthesis, and plasma antioxidant capacity of finishing lambs. Anim Feed Sci Technol 2023;305:115783. https://doi.org/10.1016/j.anifeedsci.2023.115783.

65. Yun Y, Liu T, Liu H, et al. The impact of dietary supplementation with tannic acid on the digestion of nutrients, rumen microflora, rumen fermentation, and methane production in Liuyang black goats. Anim Biosci 2026;39:250114. https://doi.org/10.5713/ab.25.0114.

66. Liu Y, Ma T, Chen D, et al. Effects of tea saponin supplementation on nutrient digestibility, methanogenesis, and ruminal microbial flora in Dorper crossbred ewe. Animals 2019;9:29. https://doi.org/10.3390/ani9010029.

67. Yang WZ, Benchaar C, Ametaj BN, Chaves AV, He ML, McAllister TA. Effects of garlic and juniper berry essential oils on ruminal fermentation and on the site and extent of digestion in lactating cows. J Dairy Sci 2007;90:5671–81. https://doi.org/10.3168/jds.2007-0369.

68. Hundal JS, Wadhwa M, Bakshi MPS. Effect of supplementing essential oils on the in vitro methane production and digestibility of wheat straw. J Anim Res Nutr 2016;1:14. https://doi.org/10.21767/2572-5459.100014.

69. Kotsampasi B, Tsiplakou E, Christodoulou C, et al. Effects of dietary orange peel essential oil supplementation on milk yield and composition, and blood and milk antioxidant status of dairy ewes. Anim Feed Sci Technol 2018;245:20–31. https://doi.org/10.1016/j.anifeedsci.2018.08.007.

70. Chagas JC, Ramin M, Exposito RG, Smidt H, Krizsan SJ. Effect of a low-methane diet on performance and microbiome in lactating dairy cows accounting for individual pre-trial methane emissions. Animals 2021;11:2597. https://doi.org/10.3390/ani11092597.

71. Zhang H, Lang X, Zhang Y, Wang C. Distribution of bacteria in different regions of the small intestine with Zanthoxylum bungeanum essential oil supplement in small-tailed Han sheep. Front Microbiol 2022;13:1062077. https://doi.org/10.3389/fmicb.2022.1062077.

72. Sun J, Cheng Z, Zhao Y, Wang Y, Wang H, Ren Z. Influence of increasing levels of oregano essential oil on intestinal morphology, intestinal flora and performance of Sewa sheep. Ital J Anim Sci 2022;21:463–72. https://doi.org/10.1080/1828051X.2022.2048208.

73. Muñoz-Cuautle A, Ortega-Cerrilla ME, Herrera-Haro JG, et al. Effect of oregano (Lippia graveolens) essential oil as a phytogenic feed additive on productive performance, ruminal fermentation, and antioxidant activity in lamb meat. Agriculture 2022;12:973. https://doi.org/10.3390/agriculture12070973.

74. Ritt LA, Orso C, Silveira AK, et al. Oregano extract fed to pre-weaned dairy calves. Part 1: effects on intake, digestibility, body weight, and rumen and intestinal bacteria microbiota. Livest Sci 2023;269:105165. https://doi.org/10.1016/j.livsci.2023.105165.

75. Zhong RZ, Yu M, Liu HW, Sun HX, Cao Y, Zhou DW. Effects of dietary Astragalus polysaccharide and Astragalus membranaceus root supplementation on growth performance, rumen fermentation, immune responses, and antioxidant status of lambs. Anim Feed Sci Technol 2012;174:60–7. https://doi.org/10.1016/j.anifeedsci.2012.02.013.

76. Yang G, He W, Ma B, et al. Effects of dietary supplementation with astragalus polysaccharides on growth performance, serum parameters, and rumen microbial function of yaks. BMC Microbiol 2026;26:64. https://doi.org/10.1186/s12866-025-04581-5.

77. Bao X, Chen L, Guo G, Huo W, Wang C, Liu Q. Dietary coated astragalus polysaccharide supplementation modulates growth performance, nutrient digestibility, rumen fermentation, and serum metabolites in Angus bulls. Anim Feed Sci Technol 2026;335:116680. https://doi.org/10.1016/j.anifeedsci.2026.116680.

78. Zhao J, Tian H, Kong X, et al. Microbiomic and metabolomic insights into the mechanisms of alfalfa polysaccharides and seaweed polysaccharides in alleviating diarrhea in pre-weaning Holstein calves. Animals 2025;15:485. https://doi.org/10.3390/ani15040485.

79. Zafarian R, Manafi M. Effect of garlic powder on methane production, rumen fermentation and milk production of buffaloes. Annu Rev Res Biol 2013;3:1013–9.

80. Fiesel A, Gessner DK, Most E, Eder K. Effects of dietary polyphenol-rich plant products from grape or hop on pro-inflammatory gene expression in the intestine, nutrient digestibility and faecal microbiota of weaned pigs. BMC Vet Res 2014;10:196. https://doi.org/10.1186/s12917-014-0196-5.

81. Gessner DK, Fiesel A, Most E, et al. Supplementation of a grape seed and grape marc meal extract decreases activities of the oxidative stress-responsive transcription factors NF-κB and Nrf2 in the duodenal mucosa of pigs. Acta Vet Scand 2013;55:18. https://doi.org/10.1186/1751-0147-55-18.

82. Verhelst R, Schroyen M, Buys N, Niewold T. Dietary polyphenols reduce diarrhea in enterotoxigenic Escherichia coli (ETEC) infected post-weaning piglets. Livest Sci 2014;160:138–40. https://doi.org/10.1016/j.livsci.2013.11.026.

83. Zhu C, Wu Y, Jiang Z, et al. Dietary soy isoflavone attenuated growth performance and intestinal barrier functions in weaned piglets challenged with lipopolysaccharide. Int Immunopharmacol 2015;28:288–94. https://doi.org/10.1016/j.intimp.2015.04.054.

84. Qiu Y, Nie X, Yang J, et al. Effect of resveratrol supplementation on intestinal oxidative stress, immunity and gut microbiota in weaned piglets challenged with deoxynivalenol. Antioxidants 2022;11:1775. https://doi.org/10.3390/antiox11091775.

85. Liu Y, Xiao Y, Xie J, et al. Dietary supplementation with flavonoids from mulberry leaves improves growth performance and meat quality, and alters lipid metabolism of skeletal muscle in a Chinese hybrid pig. Anim Feed Sci Technol 2022;285:115211. https://doi.org/10.1016/j.anifeedsci.2022.115211.

86. Liu Y, Peng Y, Chen C, et al. Flavonoids from mulberry leaves inhibit fat production and improve fatty acid distribution in adipose tissue in finishing pigs. Anim Nutr 2024;16:147–57. https://doi.org/10.1016/j.aninu.2023.11.003.

87. Chen C, Feng F, Qi M, et al. Dietary citrus flavonoids improved growth performance and intestinal microbiota of weaned piglets via immune function mediated by TLR2/NF-κB signaling pathway. J Agric Food Chem 2024;72:16761–76. https://doi.org/10.1021/acs.jafc.4c03401.

88. Gan Z, Wei W, Li Y, et al. Curcumin and resveratrol regulate intestinal bacteria and alleviate intestinal inflammation in weaned piglets. Molecules 2019;24:1220. https://doi.org/10.3390/molecules24071220.

89. Zhang L, Zhang J, Yan E, et al. Dietary supplemented curcumin improves meat quality and antioxidant status of intrauterine growth retardation growing pigs via Nrf2 signal pathway. Animals 2020;10:539. https://doi.org/10.3390/ani10030539.

90. Li X, Zhu J, Lin Q, et al. Effects of curcumin on mitochondrial function, endoplasmic reticulum stress, and mitochondria-associated endoplasmic reticulum membranes in the jejunum of oxidative stress piglets. J Agric Food Chem 2022;70:8974–85. https://doi.org/10.1021/acs.jafc.2c02824.

91. Brus M, Dolinšek J, Cencič A, Škorjanc D. Effect of chestnut (Castanea sativa Mill.) wood tannins and organic acids on growth performance and faecal microbiota of pigs from 23 to 127 days of age. Bulg J Agric Sci 2013;19:841–7.

92. Yang C, Zhang L, Cao G, et al. Effects of dietary supplementation with essential oils and organic acids on the growth performance, immune system, fecal volatile fatty acids, and microflora community in weaned piglets. J Anim Sci 2019;97:133–43. https://doi.org/10.1093/jas/sky426.

93. Li P, Piao X, Ru Y, Han X, Xue L, Zhang H. Effects of adding essential oil to the diet of weaned pigs on performance, nutrient utilization, immune response and intestinal health. Asian-Australas J Anim Sci 2012;25:1617–26. https://doi.org/10.5713/ajas.2012.12292.

94. Hsu JE, Lo SH, Lin YY, Wang HT, Chen CY. Effects of essential oil mixtures on nitrogen metabolism and odor emission via in vitro simulated digestion and in vivo growing pig experiments. J Sci Food Agric 2022;102:1939–47. https://doi.org/10.1002/jsfa.11531.

95. Wang Y, Li J, Wang H, et al. Effects of essential oil coated with glycerol monolaurate on growth performance, intestinal morphology, and serum profiles in weaned piglets. Anim Biosci 2023;36:753–60. https://doi.org/10.5713/ab.22.0261.

96. Artuso-Ponte V, Moeller S, Rajala-Schultz P, et al. Supplementation with quaternary benzo(c)phenanthridine alkaloids decreased salivary cortisol and Salmonella shedding in pigs after transportation to the slaughterhouse. Foodborne Pathog Dis 2015;12:891–7. https://doi.org/10.1089/fpd.2015.2009.

97. Li X, Li J, Zhang B, Yang B. Multidimensional impacts of Achyranthes bidentata polysaccharide supplementation on weaned piglets: from nutrient metabolism to systemic antioxidant enhancement. Res Vet Sci 2025;199:106020. https://doi.org/10.1016/j.rvsc.2025.106020.

98. Deng J, Zhang F, Fan H, et al. Effects of plant polysaccharides combined with boric acid on digestive function, immune function, harmful gas and heavy metal contents in faeces of fatteners. Animals 2024;14:1515. https://doi.org/10.3390/ani14111515.

99. Liu C, Chen H, Chen K, et al. Sulfated modification can enhance antiviral activities of Achyranthes bidentata polysaccharide against porcine reproductive and respiratory syndrome virus (PRRSV) in vitro. Int J Biol Macromol 2013;52:21–4. https://doi.org/10.1016/j.ijbiomac.2012.09.020.

100. Yang Y, Liu Y, Lou R, et al. Glycyrrhiza polysaccharides inhibits PRRSV replication. Virol J 2023;20:140. https://doi.org/10.1186/s12985-023-02052-9.

Article information Continued

This is an open-access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

S.No	Plant bioactive compounds	Species	Doses	Biological effects	References
1	Quercetin	Chicken	1 g/kg of basel diet for 42 d	Improved health condition, growth performance and meat quality, inhibited low-density lipoprotein oxidation, protected erythrocytes from oxidative damage	[38]
2	Lycium barbarum flavonoids	Ducks	500 mg/kg of basel diet for 42 d	Improved growth performance, intestinal barrier function, immune response, and antioxidant capacity in ducks	[45]
3	Turmeric extracts, containing curcumin and turmerones (TF-36)	Chicken	1% of basel diet for 42 d	Contributed to improved gut integrity and nutrient utilization, and enhanced the growth performance.	[41]
4	Curcumin	Chicken	200 mg/kg of basel diet for 42 d	Enhanced body weight gain and feed efficiency during the finishing stage, although no marked effects were observed during the starting period.	[42]
5	Curcumin	Chicken	150 mg/kg of basel diet for 28 d	Curcumin protected the AFB1-induced liver injury, through the synergistic actions of increased antioxidant capacities and inhibition of the CYP450 isozyme	[43]
6	Lycopene	Chicken	20–80 mg/kg of basel diet for 35 d	Improved reproductive efficiency in hens by elevating hepatic and systemic antioxidant defenses. Increased SOD, T-AOC, glutathione peroxidase, and GSH/GSSG ratios, reduced serum cholesterol and elevated HDL-cholesterol and triiodothyroxine.	[44]
7	Isoquinoline alkaloids	Chicken	0.6 mg/kg of basal diet	Supplementation enhanced immunity, suppressed LPS-induced hepatic inflammatory cytokines and caspase activity, and downregulated genes associated with the TLR4/MyD88/NF-κB signaling pathway.	[55]
8	Essential oil/trans-cinnamaldehyde	Chicken	1% and 1.5% of basel diet for 49 d	Salmonella infection effectively controlled by cinnamaldehyde supplementation, which reduced bacterial colonization, horizontal extent, and egg contamination	[51]
9	Astragalus polysaccharides	Chicken	1–4 mg/mL	Enhanced intestinal mucosal immunity in newcastle disease–vaccinated chickens. Increased jejunal villus height-to-crypt depth ratios, IgA⁺ cell abundance, and secretory IgA levels, and improved gut immune responses.	[52]
10	Polysaccharides from Ginseng, Astragalus polysaccharide, and Salvia miltiorrhiza	Chicken	1,000 mg/kg of basel diet for 42 d	Improved the growth performance, strengthened the immune responses by elevating serum immunoglobulins and regulating cytokines, and increased antioxidant enzyme activity and volatile fatty acids	[15]
11	Organo sulfur compounds from onion	Chicken	1 % onion extract in drink water+basal diet	Lowered blood glucose, stimulated the central nervous system, and increased feed intake, collectively enhanced metabolic activity and promoted significant body-weight gain	[53]

S.No	Plant bioactive compounds	Species	Doses	Biological effects	References
1	Quercetin	Beef cattle	42 ppm and 75 d	Slightly increased loin pH and cohesiveness but showed limited effects on antioxidant status and meat quality.	[57]
2	Hesperidin and naringin	Dairy ewes	6,000 mg/kg of feed for 28 d	Improved milk oxidative stability, reduced malondialdehyde levels, without altering milk yield, composition, fatty acid profile, or coagulation properties.	[62]
3	Citrus flavonoids	Holstein bulls	0.04% and 168 d	Improved rumen health, reduced stress behaviors, and modulated feeding without affecting overall growth performance.	[61]
4	Mulberry flavonoids and resveratrol	Sheep	2 g and 0.5 g and 8 d	Improved nutrient digestibility and energy use while reducing CH₄ and CO₂ emissions; resveratrol was more effective.	[59]
5	Tannic acid	Black goats	2% Tannic acid, g/kg diet and 20 d	Dietary tannic acid reduced methane emissions and improved feed efficiency by modulating rumen fermentation patterns and altering microbial community composition.	[65]
6	Tea saponin	Dorper cross bred ewe	2 g/d/head	Improved rumen fermentation and nutrient utilization, reducing methane by 8.8% and enhancing propionate and Fibrobacter succinogenes abundance and lowering ammonia and protozoa populations.	[66]
7	Oregano essential oil (OEO)	Lamb	0.02% and 0.04% of basel diet and 60 d	Did not affect growth, rumen traits, or carcass yield but enhanced meat antioxidant activity, crude protein stability, and shelf life, indicating improved meat quality without compromising performance.	[73]
8	Astragalus membranaceus polysaccharides	Lamb	15 g/kg of basel diet and 30 d	Enhanced rumen fermentation, antioxidant enzyme activity, and immunity, reducing cortisol without affecting growth or nutrient digestibility.	[75]
9	Astragalus polysaccharides	Yaks	1 g/kg of basel diet and 60 d	Enhanced growth performance and immune function and also optimized the rumen microbial composition. The relative abundance of Methanobrevibacter and Butyrivibrio, microbes associated with fiber degradation, anti-inflammatory activity, and immune regulation, was markedly increased.	[76]
10	Dietary coated Astragalus polysaccharide	Angus bulls	1.8 g/kg of dry matter and 60 d	Effectively improved growth performance, rumen functionality, metabolic efficiency, and serum antioxidant capacity in Angus bulls.	[77]
11	Alfalfa and sea weeds polysaccharides	Calves	4 g/calf/day with basal diet and 56 d	Alfalfa and sea weeds polysaccharides supplementation reduced diarrhea incidence in calves by modulating gut microbiota, increasing beneficial bacteria, and reducing pathogenic populations. They also regulated immune and inflammatory pathways, alleviating intestinal inflammation, with sea weeds showing greater effectiveness than alfalfa polysaccharides.	[78]
12	Organo sulfur compounds from garlic	Buffalo	2% of dry matter and 112 d	Reduced methane emissions and increased milk yield without altering digestibility or milk composition.	[79]

S.No	Plant bioactive compounds	Species	Doses	Biological effects	References
1	Quercetin	Growing pigs	0.1% of basal diet and 28 d	Improved growth, nutrient digestibility, and immune responses in LPS-challenged pigs, indicating immunomodulatory and growth-promoting effects.	[25]
2	Puerarin	Piglets	Dosage of 0.5 mg/kg body weight	Enhanced intestinal antioxidant defenses in PEDV-challenged piglets, increasing SOD and GSH-Px and reducing H₂O₂ and MDA.	[26]
3	Soy isoflavone	Weaned piglets	40 mg/kg of basal diet and 14 d	Enhanced immune function, reduced diarrhea incidence, and decreased circulating endotoxin levels in LPS-challenged piglets.	[83]
4	Citrus flavonoids	Weaned piglets	80 mg/kg of basal diet and 28 d	Flavonoid supplementation improved piglet growth and intestinal health potentially through modulation of the TLR2/NF-κB signaling pathway. This intervention was associated with a reshaping of the gut microbiota, characterized by increased relative abundances of Bacteroidetes and Prevotella, alongside reductions in Tenericutes and Clostridiales, collectively indicative of a more balanced intestinal microbial community.	[87]
5	Resveratrol	Weaned piglets	300 mg/kg of basal diet and 28 d	Reduced deoxynivalenol-induced intestinal inflammation and oxidative stress, enhancing microbial balance and intestinal barrier integrity in piglets.	[84]
6	Curcumin	Weaned piglets	300 mg/kg and 400 mg/kg or 300 mg/kg or 200 mg/kg of basel diet and 14–28 d	Increased IL-10 expression and secretory IgA, while reducing TLR4, TNF-α, IL-1β expression and intestinal damage markers. Also it alleviated oxidative stress and protected the structural integrity and reduced the intestinal copy number of pathogenic Escherichia coli, downregulated the TLR4 signaling pathway.	[88,90]
7	Curcumin	Growing pigs	200 mg/kg of basel diet and 26 to 115 d	Improved leg muscle redox status and meat quality in IUGR offspring by mitigating oxidative stress.	[89]
8	Mixture of chestnut wood tannins and organic acids	Piglets	0.35% additive containing (0.19% and 0.16% of organic acids) 23 to 127 d	The improvement in animal growth performance observed between d 82 and 127 may be associated with a reduction in pathogenic E. coli and a concomitant increase in beneficial lactic acid bacteria.	[91]
9	Essential oils containing thymol, cinnamaldehyde, and carvacrol	Weaning pigs and growing pigs	0.01% of basel diet and 35 d	The treatment improved overall animal performance and reduced the incidence of diarrhea, potentially through coordinated effects on immune function, intestinal microbial balance, and nutrient digestibility.	[93]
10	Achyranthes bidentata polysaccharides	Weaned piglets	800 mg/kg and 1,600 mg/kg of basel diet and 28 d	The intervention improved mineral homeostasis, hepatic function, lipid metabolism, immune responses, and resilience to oxidative stress in weaned piglets.	[97]