Modern pig production faces multiple interconnected challenges, including the improvement of feed efficiency and animal health, the need to meet the growing demands of consumers, compliance with food safety regulations, and the achievement of environmental sustainability. In this context, feed additives play an important role in nutritional strategies by supporting the proper functioning of the pig gastrointestinal tract. Such support enhances digestive enzyme activity and positively influences intestinal fermentation, leading to higher production of short-chain fatty acids (SCFAs), especially butyrate. The use of feed additives further contributes to the reduction of protein fermentation metabolites, such as ammonia and branched-chain fatty acids, thereby supporting the maintenance of a stable and healthy intestinal environment. Feed additives also improve intestinal structure by increasing villus height, reducing crypt depth, and enhancing the villus-to-crypt ratio in the small intestine, which facilitates nutrient absorption. Furthermore, reinforcement of intestinal barrier integrity is achieved through stimulation of SCFA production, enhancement of nutrient digestibility, and support of beneficial microbiota development and immune system mechanisms (Valenzuela-Grijalva et al., 2017).
Contemporary functional feed additives not only enhance production efficiency and reduce costs, but also reduce the need for pharmacological interventions, which results in better animal welfare and aligns with growing societal demands for sustainable livestock production (Ángel-Isaza et al., 2024) (e.g., probiotics improving gut microbiota balance, enzymes increasing nutrient digestibility, prebiotics stimulating beneficial bacterial growth). Their use is particularly important during physiologically sensitive phases of production, such as pig weaning or the periparturient period in sows when animals are more vulnerable to metabolic disorders and infections (Jeon et al., 2024; Konieczka et al., 2023; Liu et al., 2025).
In light of increasing restrictions on the use of antibiotics in animal nutrition, driven by the rise of antimicrobial resistance and tightening legislation, probiotics have emerged as a scientifically validated and safe alternative to antibiotic growth promoters. Probiotics are live microorganisms that, when provided in adequate amounts, confer health benefits to the host by stabilizing the intestinal microbiota, competing with pathogens, stimulating the immune system, and strengthening the intestinal barrier (Narzary, 2025). A growing body of research has demonstrated that supplementation in swine diets is associated with improved growth performance and feed conversion efficiency, a reduced incidence of diarrhoea, and beneficial modulation of haematological and serum biochemical parameters (Czech et al., 2018 a, b). Probiotics (e.g. B. licheniformis + B. subtilis, 2 × 1010 CFU/kg feed, 28–83 d) also exert their effects by producing antimicrobial substances such as bacteriocins and organic acids, which inhibit pathogenic bacteria. Such activity contributes to disease prevention and supports herd-level biosecurity and reduces the need for therapeutic antibiotic use, which is crucial for herd health and food safety (Czech et al., 2018 a).
This review aims to summarize recent advances in the application of probiotics in swine nutrition, with particular focus on their efficacy and mechanisms of action across distinct physiological stages, from the weaning period in pigs, through the growing-finishing phase, to gestating and lactating sows, providing an integrated perspective on their contribution to sustainable pig production.
Mechanisms of probiotic action
The mechanisms by which probiotics exert their effects are multifaceted and remain only partially elucidated. One of the primary mechanisms is competitive exclusion, whereby probiotics compete with pathogenic bacteria for epithelial binding sites and receptors, thereby reducing pathogen colonization and limiting their ability to establish infections (Shin et al., 2019).
Adhesion of probiotic microorganisms to the gut epithelium represents the initial and essential step in colonization and host interaction (Plaza-Díaz et al., 2019). Probiotic strains such as Lactobacillus mucosae LM1 and Lactobacillus johnsonii PF01 strains utilize specific surface proteins, known as adhesins (e.g., fibrinogen-binding proteins, mucin-binding proteins), to interact with receptors located on the surface of enterocytes, including membrane glycoproteins and glycolipids (Valeriano et al., 2016).
The adhesion process involves hydrophobic, hydrogen, and electrostatic interactions between bacterial adhesin proteins and the oligosaccharide residues of host glycoproteins and glycolipids, thereby stabilizing bacterial contact with enterocytes (Nishiyama et al., 2016). In certain Lactobacillus strains, such as L. fermentum, the mucin-binding domains (MBDs) of their MucBP proteins recognize specific mucin-associated sugar residues (e.g., N-acetylgalactosamine, N-acetylglucosamine, galactose and sialic acid), enabling strong binding to the mucus layer, including MUC2/MUC3, and facilitating colonization (Chatterjee et al., 2018).
Additionally, selected probiotic bacteria, including Lactobacillus plantarum, have been shown to modulate the expression of elongation factor Tu (EF-Tu) in response to mucin, thereby enhancing adhesion to the intestinal mucus while simultaneously preventing the attachment of pathogenic microorganisms, such as Escherichia coli and Salmonella, to the same binding sites (Dhanani and Bagchi, 2013).
Following adhesion to the intestinal epithelium, probiotics are capable of activating host pattern recognition receptors (PRRs), including Toll-like receptors 2 and 4 (TLR2 and TLR4) as well as NOD1/NOD2. Structural components of probiotic cells, such as peptidoglycans and lipoteichoic acids, act as ligands for these receptors, thereby initiating intracellular signalling cascades involving adaptor proteins like MyD88 (Han et al., 2019). Subsequent activation of the NF-κB and MAPK pathways regulates the expression of genes encoding both pro-inflammatory (e.g., TNF-α, IL-6) and anti-inflammatory (e.g., IL-10) cytokines, contributing to the maintenance of mucosal immune homeostasis (Saxelin et al., 2005; Zagato et al., 2014).
It has been demonstrated that lipoteichoic acid (LTA) from Lactobacillus plantarum modulates NOD2 expression and inhibits NF-κB activation in human macrophages (Kim et al., 2008). Moreover, LTA suppresses NF-κB activation in human intestinal epithelial cells, resulting in the inhibition of IL-8 production (Noh et al., 2015). The anti-inflammatory action of LTA supports the regulation of barrier-related proteins, such as zonula occludens-1 (ZO-1) and occludin, in intestinal epithelial cells, thereby contributing to the improvement of barrier function. For instance, Lactobacillus acidophilus LA1 promotes the reinforcement of tight junction integrity in a TLR2-dependent manner (Al-Sadi et al., 2021). In addition, conditioned medium from L. acidophilus prevents the IL-1β-induced reduction of occludin in Caco-2 cells (Wang et al., 2018). In the longer term, these interactions increase mucin secretion by goblet cells, thereby reinforcing the mucus layer and enhancing protection against pathogens. Goblet cells produce rod-shaped, highly glycosylated mucins which adhere to the epithelial surface or are released into the intestinal lumen. These mucins form a glycoprotein matrix through disulphide bonds, protecting the epithelium from digestive enzymes and pathogens while also supporting intestinal motility (Lundin et al., 2008). In vitro studies have demonstrated that conditioned medium from Lactobacillus casei T21 regulates the expression of the mucin gene MUC2 in Caco-2 and HT29 cells exposed to Clostridioides difficile (Panpetch et al., 2021). Similar findings were reported for L. casei GG in Caco-2 cells (Mattar et al., 2002), suggesting that probiotics stimulate mucin secretion independently of lactic acid itself. Through these mechanisms, probiotics reinforce the mucus layer, enhance intestinal barrier integrity, and support immune homeostasis, in part via the stimulation of antimicrobial peptide production, such as defensins (Sang and Blecha, 2009). In the porcine gastrointestinal tract, α-defensins are produced primarily by Paneth cells in the small intestine, whereas β-defensins are synthesized by enterocytes and goblet cells throughout the whole intestine. The expression of β-defensins (e.g., pBD-1, pBD-2, pBD-4) is genetically regulated and reflects the complexity of the host defence system (Choi et al., 2012). The underlying mechanism of defensin activity involves electrostatic binding to bacterial membranes, insertion into the lipid bilayer, and pore formation, ultimately leading to the lysis of pathogenic cells (Veldhuizen et al., 2008). In addition, pBD-2 has been shown to modulate the immune response by inhibiting inflammation induced by E. coli through blockade of the TLR-NF-κB/MAPK signalling pathways (Shen et al., 2024).
Beyond their immunomodulatory effects, probiotics strengthen intestinal barrier integrity through the regulation of tight junction proteins such as claudins, occludin, and ZO-1. This results in reduced epithelial permeability and limited translocation of microorganisms into the systemic circulation (Plaza-Díaz et al., 2019). In pigs, these effects have been confirmed in in vivo studies. Dietary supplementation with Lactobacillus plantarum in weaned pigs mitigated the E. coli-induced reduction in both mRNA and protein expression of claudin-1, occludin, and ZO-1 (Yang et al., 2014). Administration of Bacillus licheniformis S6 increased both the transcription and protein levels of ZO-1 and occludin in the intestinal mucosa, as demonstrated by Western blot and mRNA analyses (Sun et al., 2023). Simultaneously, probiotics stimulate mucus secretion by goblet cells, increasing the density of the mucus layer and constituting a crucial first line of defence against pathogens. In weaned pigs supplemented with Lactobacillus plantarum 299v, probiotic administration improved intestinal barrier function, as evidenced by increased expression of tight junction proteins, including zonula occludens-1 and occludin. These changes were accompanied by enhanced intestinal morphology, reflected by increased villus height and reduced crypt depth, indicating improved absorptive capacity and a reinforced epithelial barrier (Wang et al., 2019 b).
In summary, probiotics exert complex, interrelated multifactorial effects that include activation of the innate immune response, reinforcement of structural and functional gut barrier integrity, and favourable modulation of the gut microbiota composition. Collectively, these mechanisms enhance intestinal resilience and metabolic efficiency and support the position of probiotics as a key component of strategies aimed at supporting gastrointestinal health in pigs and other monogastric species.
Probiotics used in swine nutrition
Among the most widely used probiotics in pig nutrition are representatives of the genera Lactobacillus, Bifidobacterium, Saccharomyces, and Enterococcus, all of which have well-documented immunomodulatory, antimicrobial, and metabolic properties (Duarte and Kim, 2024; Hu et al., 2019; Pang et al., 2022).
The best-characterized and most frequently applied strains belong to the genus Lactobacillus, including Lactobacillus acidophilus, L. casei, and L. reuteri. Lactobacillus strains exhibit the ability to colonize the intestinal mucosa, produce lactic acid, and compete with pathogens for adhesion sites and nutrients. According to Yi et al. (2018), supplementation with L. reuteri LR1 at a dose of 5 × 1010 CFU/day in suckling pigs improved intestinal barrier integrity and reduced the incidence of diarrhoea.
Dietary supplementation with Bifidobacterium animalis subsp. lactis (1 × 1010 CFU/kg) in weaned piglets has been shown to improve growth performance and reduce diarrhoea. The treatment increased villus height in the duodenum, elevated goblet cell numbers and amylase activity in the jejunum, and enhanced antioxidant capacity by increasing total antioxidant capacity and decreasing malondialdehyde content in jejunal mucosa. No effects on the mRNA expression of genes associated with intestinal barrier function and inflammatory cytokines were observed. Microbiota analysis indicated an increase in beneficial bacteria and a decrease in pathogenic bacteria such as Helicobacter and Escherichia-Shigella. These results indicate the potential of B. animalis as a probiotic feed additive for weaned piglets (Pang et al., 2022).
Yeast strains from the genus Saccharomyces, particularly Saccharomyces cerevisiae var. boulardii, are also widely applied as probiotic supplements. Documented effects include bacterial toxin binding, stabilization of intestinal pH, and stimulation of enzymatic activity. Duarte and Kim (2024) reported that supplementation with yeast-derived postbiotics (celluTEIN) at a dose of 175 g/ton of feed during the weaning period reduced diarrhoea incidence in the first week post-weaning and preserved villus integrity by enhancing immune responses, stimulating crypt cell proliferation, and downregulating genes associated with apoptosis without affecting inflammation, oxidative stress, or growth rate in pigs.
Another important group of probiotics used in swine diets includes bacteria from the genus Enterococcus, particularly Enterococcus faecium. Dietary supplementation with Enterococcus faecalis LAB31 at a dose of 2.5 × 109 CFU/kg improved growth performance in weaned pigs, increasing average daily gain (≈ 348 vs. 312 g/day in the control) and feed efficiency (FCR ≈ 1.69 vs. 1.77 in the control), while reducing the diarrhoea index (3% vs. 6.6% in the control) to a level comparable to neomycin-treated animals (3.6%). Additionally, this strain increased the relative abundance of Lactobacillus in faeces and modulated gut microbiota composition, supporting its potential as an effective alternative to antibiotic growth promoters (Hu et al., 2015).
Next-generation probiotics in swine nutrition
In recent years, increasing attention has been devoted to next-generation probiotics (NGPs) in pigs nutrition. These strains extend beyond classical species such as Lactobacillus and Bifidobacterium, offering targeted immunomodulatory, metabolic, and mucosal protective effects. Notable representatives include Akkermansia muciniphila, Faecalibacterium prausnitzii, functionally active strains of Clostridium butyricum, Limosilactobacillus reuteri with defined metabolic activity, and Bacteroides uniformis (Narzary, 2025).
One of the best-characterized NGPs is Akkermansia muciniphila, a mucin-degrading bacterium that contributes to the homeostasis of the intestinal mucus layer. Although its application in pig remains at an early experimental stage, current evidence suggests promising potential for enhancing gut barrier function and host metabolism. Lan et al. (2024) demonstrated that supplementation of weaned pigs with A. muciniphila at a dose of 5 × 108 CFU/5 mL (administered via oral gavage every other day for 28 days) improved small intestinal morphology, increased the proportion of circulating CD4+ lymphocyte counts, and upregulated genes associated with barrier integrity and antioxidant responses. Simultaneously, the treatment downregulated Escherichia coli (ETEC) virulence factor genes in the ileum and colon, indicating a dose- and form-dependent protective effect of A. muciniphila on gut health in weaned pigs.
Among the more extensively studied NGP candidates, selected strains of Clostridium butyricum, particularly MIYAIRI 588, have demonstrated precise and strain-specific functionality (Hirata et al., 2022). Casas et al. (2020) demonstrated that dietary supplementation with C. butyricum at doses of 1.25–3.5 × 108 CFU/kg increased ADG, G:F, and final body weight during phase 2 and across the overall experimental period, with no changes observed in immunological parameters. Additionally, C. butyricum supplementation did not affect microbial diversity in the ileum or colon, despite clear differences in microbiota composition between these intestinal segments. The results indicate its efficacy as a viable alternative to in-feed antibiotics.
Another well-documented NGP is Limosilactobacillus reuteri DSM 17938, a producer of reuterin, a naturally occurring antimicrobial compound (Lee et al., 2025 a). Wu et al. (2024) found that supplementation with L. reuteri SLZX19-12 (1.38 × 108 CFU/kg) in weaned pigs raised under low-hygiene conditions significantly reduced diarrhoea, improved growth performance, enhanced intestinal barrier integrity, and modulated the gut microbiota. These effects were attributed to inhibition of the NF-κB p65 inflammatory pathway in the ileum and colon, increased levels of short-chain fatty acids and bile acids, and improved small intestinal morphology, highlighting the strain's potential in alleviating post-weaning stress.
Recently, certain strains of Bacteroides uniformis have attracted increasing interest for their immunoregulatory properties (Tan et al., 2019). Yong et al. (2019) demonstrated that these factors (e.g., heat stress, weaning, transportation stress, and other environmental or management-related stressors) can influence immune function by modulating the balance between regulatory T cells (Treg) and Th17 cells, a mechanism crucial for controlling inflammatory responses in the gastrointestinal tract. Such immune-modulating activity is particularly relevant in the context of intestinal health in pigs, particularly during critical phases such as weaning, when animals are highly susceptible to immune dysregulation and enteric infections.
Application of probiotics in pig nutrition
The weaning period represents one of the most critical stages in a pig's life, due to abrupt changes in environment and diet, as well as exposure to multiple stressors that disrupt gut microbiota balance. Consequently, weaned pigs often experience reduced feed intake, growth retardation, impaired intestinal barrier function, and increased susceptibility to bacterial diarrhoea, primarily caused by Escherichia coli (Duarte and Kim, 2024). Given the restrictions on antibiotic growth promoters, probiotics have emerged as a promising nutritional strategy to support pig health and production efficiency. Numerous studies have demonstrated that dietary supplementation can improve growth performance and feed utilization in pigs (Table 1).
Table 1.
Effects of probiotic supplementation in different technological groups of pigs (% change relative to the control group)
| Technological group | Period | Probiotic/dose | Production indicators | Nutrient digestibility | Health parameters | Microbiology indicators | Meat quality | Emissions | References |
|---|---|---|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
| PIGS | 27–56 d of life | Bacillus licheniformis, Bacillus subtilis/2 × 109 CFU/kg feed |
|
|
| E. coli in faeces ↓~26% | Czech et al. (2018 a, b) | ||
| PIGS | ~23.3– ~109 kg body weight |
|
|
|
|
| NH3, H2S – T1, T2 – ns | Balasubramanian et al. (2016) | |
| PIGS | ~7– ~25 kg body weight |
|
|
|
|
|
| Cao et al. (2025) | |
| PIGS | ~8– ~14 kg body weight |
|
|
|
|
| Han et al. (2020) | ||
| PIGLETS | 6–18 d of life | Bacillus amylo liquefaciens/4 0x1.0 × 109 C FU/mL-1 mL/day by oral gavage | Average diarrhoea scores ↓ p ≤0.05 |
| Jiang et al. (2023) | ||||
| FINISHER PIGS | ~28– ~112 kg body weight | Bacillus licheniformis/1.6 × 109 CFU/g, and Bacillus subtilis/1.6 × 109 CFU/g – dose 0.04% |
|
| Meat quality and basic chemical composition – ns | Rybarczyk et al. (2021) | |||
| FINISHER PIGS | ~18– ~100 kg body weight |
|
| Dry matter T3 ↑~1% |
| Lactobacillus in faecal T3 ↑~1% | H2S ↓~5% | Jeon et al. (2024) | |
| FINISHER PIGS | ~7.5– ~100 kg body weight | 0.01% L. plantarum/1.0 × 109 CFU/g, S. thermophilus/1.0 × 107 CFU/g, Bacillus spp./3.0 × 109 CFU/g | Live body weight ↑~1% | Carcass traits – ns Protein in the longissimus dorsi muscle ↑~6% | Lee et al. (2025 a) | ||||
| SOWS | 90 d of gestation –end of lactation | 0.04% – 2.75 × 109 CFU/g viable spores of B. subtilis, B. amyloliquefaciens |
|
| Konieczka et al. (2023) | ||||
| PIGLETS | 7–28 d of life |
|
| ||||||
| SOWS | gestation and lactation | Lactobacillus fermentum/1 × 108 CFU/ml, Basidiomycetous yeast/8 × 107 CFU/mL – 200 ml/day |
|
| Wu et al. (2023) |
Cao et al. (2025) reported that weaned pigs receiving a Bacillus-based probiotic complex containing Bacillus subtilis (1.0 × 109 CFU/g) and Bacillus licheniformis (1.0 × 109 CFU/g), supplemented to the basal diet at graded inclusion levels (0.1%, 0.2% and 0.3%), exhibited a linear improvement in growth performance. In particular, the 0.3% inclusion level resulted in a significantly higher average daily gain (ADG) and an improved feed conversion ratio (FCR) over the 42-day experimental period compared with the control group. Additionally, pigs receiving 0.3% of the probiotic showed reduced faecal concentrations of ammonia (NH3) and hydrogen sulphide (H2S), indicating more efficient nutrient utilization and a concomitant reduction in noxious gas emissions.
Similar findings were reported by Liu et al. (2017), who demonstrated that oral administration of Lactobacillus casei and Enterococcus faecalis, either individually or in combination at a 3:1 ratio, with increasing doses from 1 to 4 mL on days 1, 7, 14, and 21 of age, significantly improved average daily gain (by approximately 20%) and reduced the incidence of diarrhoea (by approximately 54%) during the 21-day period. Furthermore, diarrhoea rates seven days post-weaning decreased by more than 60%, 50%, and 70%, respectively, while, mortality was reduced by approximately 60%, 43%, and 64%, compared to the control group.
Probiotics have also been shown to effectively reduce the incidence of diarrhoea through several complementary mechanisms, including competitive exclusion of pathogens at epithelial adhesion sites, the production of antimicrobial metabolites (such as organic acids, hydrogen peroxide and bacteriocins), and modulation of the host immune response, thereby contributing to the regulation of intestinal inflammation (Sun et al., 2021). For example, Lacto-bacillus plantarum (5 × 1010 CFU/kg of diet) administered to pigs during early life, improved growth performance and effectively prevented diarrhoea induced by enterotoxigenic Escherichia coli (ETEC) K88. These effects were associated with enhanced intestinal barrier function through the protection of intestinal morphology and permeability, as well as upregulated expression of tight junction protein genes, including zonula occludens-1 and occludin (Yang et al., 2014). Similarly, Bacillus subtilis exhibited significant probiotic effects, improving post-weaning performance by increasing body weight and average daily gain (especially in BS-B and BS-C groups), reducing the incidence of diarrhoea, and enhancing intestinal function. These benefits were linked to an increased villus height and villus height-to-crypt depth ratio in the ileum, modulation of the gut microbiota (↑Anaerovibrio, Bulleidia; ↓Clostridium, Coprococcus in BS-C) and elevated levels of interleukin-2 (IL-2), interleukin-10 (IL-10) and short-chain fatty acids (SCFAs). These effects were additionally reinforced by increased expression of genes associated with microbial maturation and metabolic pathways, indicating a multifaceted influence of Bacillus subtilis on gastrointestinal function (Tian et al., 2021 b).
Hu et al. (2019) reported that administration of Enterococcus faecium reduced mortality in weaned pigs from 8.79% to 2.20%, while diarrhoea rates remained similar across groups. Similarly, a study by Li et al. (2022) showed that a mixture of Lactobacillus plantarum and Bacillus licheniformis effectively reduced E. coli counts in the jejunum and improved mucosal barrier integrity.
The immunomodulatory effects of probiotics are reflected in a range of physiological and biochemical responses. Xie et al. (2025) reported that daily supplementation of pigs with Lactobacillus reuteri (10 mL, 2.0 × 1010 CFU/mL) significantly improved intestinal barrier function and enhanced immune activity. These effects were evidenced by an increased villus height-to-crypt depth ratio in the ileum and the upregulation of tight junction proteins, including zonula occludens-1 (ZO-1) and claudin-1, which are essential for maintaining epithelial integrity. In addition, probiotic treatment reduced the expression of pro-inflammatory cytokines such as interleukin-6 (IL-6) and tumour necrosis factor-α (TNF-α), while increasing levels of the anti-inflammatory cytokine interleukin-10 (IL-10), indicating a shift towards an anti-inflammatory intestinal environment. In sows, similar immunomodula-tory mechanisms have been proposed at the level of mucosal surfaces. Probiotic L. reuteri supplementation has been associated with attenuation of pathogen-induced inflammatory signalling and modulation of epithelial immune responses, contributing to mucosal immune homeostasis. In particular, studies using vaginal epithelial cell models demonstrate that L. reuteri suppresses NF-κB-dependent expression of pro-inflammatory cytokines in response to microbial challenge, supporting a local environment conducive to barrier integrity and immune regulation (Wagner and Johnson, 2012).
Likewise, Zhang et al. (2023) found that Lactobacillus supplementation led to increased serum concentrations of immunoglobulins G (IgG) and immunoglobulin M (IgM), interferon-γ, and interleukins IL-2, IL-4, and IL-10, while reducing tumour necrosis factor-α (TNF-α) levels compared with control group. Interestingly, animals receiving higher probiotic doses showed significantly greater levels of IL-2, IL-4, and IL-10 than those receiving lower doses. These immunological responses were accompanied by shifts in the gut microbiota, including higher Lachnospiraceae abundance and reduced Terrisporobacter, suggesting their involvement in host immune modulation.
An additional important mechanism underlying probiotic efficacy is the modulation of oxidative stress, which often accompanies intestinal disturbances after weaning. Li et al. (2021) reported that supplementation with the probiotic Clostridium butyricum in pigs significantly enhanced hydroxyl radical scavenging activity and glutathione peroxidase (GSH-Px) activity, while slightly reducing serum H2O2 levels, indicating an improved redox balance. These effects may be linked to strengthened intestinal barrier function and reduced translocation of bacterial endotoxins.
Application of probiotics in fattening pig nutrition – opportunities and limitations
Although probiotics are most extensively applied in pig nutrition where their efficacy in reducing diarrhoea incidence, improving health status, and promoting growth is well documented, interest in their potential application during the finishing phase has been increasing (Table 1). In this production stage, probiotic effectiveness tends to be less evident, partly due to the more stable colonization of the intestinal microbiota by commensal bacteria, the maturation of the immune system, and reduced exposure to environmental stressors associated with weaning. Nonetheless, research indicates that well-characterized probiotic strains, particularly those capable of modulating metabolic and immunological parameters, can significantly influence growth performance, feed efficiency, and carcass quality (Lee et al., 2025 b) (Table 1).
Potential benefits encompass improvements in intestinal barrier integrity and reductions in oxidative stress markers, although these effects depend on multiple factors, including the animals' age, basal diet composition, and environmental conditions.
Rybarczyk et al. (2021) reported that supplementation with a mixture of Bacillus subtilis and Bacillus licheniformis throughout the fattening period led to a significant improvement in feed conversion ratio (FCR) and a modest but statistically significant increase in average daily gain (ADG). Similarly, Cao et al. (2025) observed that a Bacillus-based probiotic improved growth rate, feed efficiency (F:G), and nutrient digestibility, particularly of fat and phosphorus. These positive effects were attributed to the suppression of putrefactive fermentation, stabilization of the intestinal environment, and enhanced nutrient absorption.
In fattening pigs, probiotics stabilize the intestinal microbiota by limiting the proliferation of potentially pathogenic bacteria such as Clostridium perfringens and Escherichia coli, while promoting the growth of lactic acid bacteria (Hirata et al., 2022). Although such effects are typically more pronounced in younger animals, Hirata et al. (2022) confirmed that even in older pigs, supplementation can increase the abundance of Lactobacillus spp. and improve the ratio of beneficial to opportunistic bacteria, thereby reducing the risk of diarrhoea and inflammatory disturbances.
Probiotics have the potential to influence lipid, carbohydrate, and protein metabolism in fattening pigs. In the study by Balasubramanian et al. (2016), dietary supplementation with a combination of Bacillus spp. for 16 weeks resulted in improved growth rates, feed efficiency, and nutrient digestibility. Enhanced digestibility of dry matter, along with a trend toward better nitrogen and energy utilization, suggests that probiotics may support the digestion and absorption of proteins and carbohydrates.
Additionally, probiotics may influence blood glucose levels, indicating a role in the regulation of energy metabolism. These microorganisms help modulate gut microbiota composition by promoting beneficial bacteria such as Lactobacillus spp. and reducing the abundance of pathogens like Escherichia coli, which indirectly enhances metabolic efficiency and overall health. Although some studies have not observed a consistent reduction in emissions of harmful gases (ammonia, hydrogen sulphide, thiol), probiotics can still contribute to reducing environmental pollution by improving nutrient digestibility and decreasing the amount of undigested fermentable residues in the large intestine (Cao et al., 2025).
Emerging evidence also suggests that long-term probiotic supplementation can positively influence meat quality. Tian et al. (2021 a) reported that Lactobacillus reuteri enhanced protein synthesis, possibly by modulating the expression of amino acid transporter genes and ribosomal protein S6 kinase 1 (S6K1). Moreover, the probiotic altered the fatty acid profile through regulation of metabolic pathways. Overall, supplementation with L. reuteri was found to improve pork quality by reducing drip loss and shear force, increasing levels of inosine acid and glutamic acid compounds known to enhance flavour and modifying muscle fibre characteristics.
Application of probiotics in sow nutrition
The use of probiotics in sow nutrition is becoming increasingly common, especially during the periparturient period, which is characterized by exceptionally high physiological and metabolic requirements within the reproductive cycle. Maintaining proper gastrointestinal function during this critical time is essential not only for the health of the sow but also for the condition of her offspring. Probiotic supplementation helps maintain intestinal microbiota balance, strengthens epithelial barrier integrity, and regulates immune responses, thereby reducing the risk of infections and chronic inflammation (Table 1). Scientific evidence indicates that supplementation with strains such as Lactobacillus plantarum is associated with a decreased incidence of diarrhoea in offspring of supplemented sows, improved growth performance, and enhanced physiological status. In addition, probiotic administration has been shown to modulate haematological parameters in piglets, suggesting beneficial effects on immune function and adaptation during the periparturient period (Betancur et al., 2021). Moreover, supplementation of sows with the probiotic Bacillus licheniformis DSMZ 28710 (10 g/day) from the pre-farrowing period until weaning significantly altered the microbial composition of colostrum and milk. In colostrum, an increased abundance of beneficial bacteria (Lactobacillus, Pediococcus, Bifidobacterium) and a concurrent reduction in potential pathogens (Staphylococcus aureus, Enterobacteriaceae) were observed. Similar shifts were detected in milk, including an increased relative abundance of Bacteroides, while maintaining high overall microbial diversity. Probiotic inclusion also enhanced metabolic functions related to membrane transport, suggesting potential benefits for pig immunity, health, and development (Wongsamart et al., 2025). Further evidence supporting the beneficial effects of Bacillus supplementation on immune function and intestinal development comes from studies evaluating immunological parameters in sows and their offspring. In one study, supplementation of sows throughout gestation and lactation with a mixture of Bacillus subtilis 541 and Bacillus amyloliquefaciens 516 (2.75 × 109 CFU/g) resulted in increased serum IgG concentrations in sows at parturition, as well as enhanced intestinal mucosal development in piglets, as evidenced by increased villus length and enlarged Peyer's patches. These findings suggest a sustained impact on intestinal maturation and immune competence in the offspring (Konieczka et al., 2023). Comparable effects were observed in studies evaluating the administration of a direct-fed microbial (DFM) based on Bacillus subtilis (3.75 × 105 CFU/g of feed) to sows for six weeks prior to farrowing and throughout the entire lactation period. This supplementation influenced the development of the gut microbiota in newborn piglets by increasing the abundance of beneficial strains, such as Lactobacillus gasseri/johnsonii, while simultaneously reducing the presence of potentially pathogenic E. coli and Clostridium perfringens. Litters from sows supplemented with a DFM were characterized by a higher weaning weight gain (61.32 vs. 57.91 kg), a tendency towards greater litter average daily gain (45.06 vs. 43.05 kg), a higher number of pigs weaned (9.86 vs. 9.56), and numerically lower pig mortality (10.41% vs. 12.76%), confirming the beneficial effects of supplementation on off-spring health and development (Baker et al., 2013). In a study by Liu et al. (2025), sows were orally administered a recombinant Bacillus subtilis (5 mL, 1 × 1010 CFU/mL) capable of producing 4,4′-diaponeurosporene (B.S-Dia) during the final 35 days of gestation. This intervention significantly increased pig body weight, intestinal villus height and crypt depth, and epithelial proliferative activity, as indicated by proliferating cell nuclear antigen (PCNA) and c-Myc gene expression. In addition, an increased number of goblet cells and elevated expression of antimicrobial peptides (Muc2, Lyz-1), as well as higher levels of IL-4 and IFN-γ and an increased number of CD3+ cells, were observed, indicating enhanced intestinal immune function in the offspring. Similarly, supplementation of sows with a multi-strain probiotic containing several Lactobacillus and Bacillus strains (5 g/sow/day) from 12th week of gestation until weaning significantly increased IgA concentrations in colostrum during the first hours after parturition. This supplementation was associated with a higher body weight of pigs at weaning (5.9 vs. 3.9 kg in the control group) and a lower pre-weaning mortality rate (24.9% vs. 53.6%), further confirming the beneficial effects of probiotics on offspring immunity and survival (Innamma and Kaeoket, 2025).
An increasing number of studies demonstrate that probiotics used in sow nutrition may exert a beneficial effect on oxidative status, particularly during the periparturient period, a phase characterized by intense physiological stress and redox imbalance (Table 1). Supplementation of sow diets with oregano essential oil (OEO) demonstrates potential in modulating oxidative stress parameters. Increased serum concentrations of reactive oxygen species (ROS) and thiobarbituric acid reactive substances (TBARS) were observed during late gestation and early lactation compared with early gestation. Serum 8-hydroxy-deoxyguanosine (8-OHdG) concentrations were higher during gestation and lactation than in early gestation. OEO supplementation reduced serum TBARS and 8-OHdG concentrations on day 1 of lactation. Tendencies for increased glutathione peroxidase (GSH-Px) activity (day 60 of gestation and day 1 of lactation) and decreased ROS (days 1 and 3 of lactation) and 8-OHdG (day 109 of gestation and day 3 of lactation) were also observed. These results indicate an effect of OEO supplementation on oxidative stress parameters during the periparturient period (Tan et al., 2015).
In addition to probiotics, modern functional feed additives such as prebiotics, nutraceuticals, phytobiotics, and other bioactive compounds are gaining increasing importance in swine nutrition and have become key components in improving production efficiency. These additives make it possible to simultaneously enhance productivity while reducing reliance on pharmaceutical interventions, thereby directly contributing to improved animal welfare (Ángel-Isaza et al., 2024). Research indicates that such compounds can have beneficial effects on the structure and function of the intestinal epithelium, including increased villus height and enhanced intestinal barrier integrity, ultimately resulting in more efficient nutrient absorption (Casas et al., 2020). It is worth noting that prebiotics can further enhance the activity of probiotics, forming synbiotic formulations that may surpass the efficacy of pro- or prebiotic additives when administered separately (Zhu et al., 2022). As demonstrated in previous studies, appropriately selected combinations, such as Bacillus, Lactobacillus or Bifidobacterium strains administered at doses ranging from 106 to 109 CFU per animal per day, together with prebiotics including inulin, fructooligosaccharides (FOS) or mannan-oligosaccharides (MOS), can effectively modulate the gut microbiota of pigs from the first weeks of life. For example, in studies comparing newly developed synbiotic formulations with commercial probiotics administered to piglets from day 7 of life through the post-weaning period (up to approximately 165 days of age) synbiotics more effectively supported the development of a beneficial gut micro-biota. Also, they increased lactic acid and short-chain fatty acid (SCFAs) production while simultaneously reducing the proportion of unfavourable metabolites, including branched-chain fatty acids (BCFAs). Notably, synbiotics also mitigated the adverse effects of weaning on intestinal bacterial populations, thereby reducing the risk of peri-weaning diarrhoea (Chlebicz-Wójcik and Śliżewska, 2020). The effects of synbiotics have also been confirmed in sow nutrition. In a study by Wang et al. (2021), the administration of probiotics (Lactobacillus plantarum B90 at ≥ 1 × 108 CFU/mL and Saccharomyces cerevisiae P11 at ≥ 0.2 × 108 CFU/mL) at a dose of 200 mL/day, as well as a synbiotic additionally containing 500 g/t XOS (≥ 35%), in the diet of sows during gestation and lactation significantly modulated the microbiota and metabolome of their offspring. Significant differences in the composition of the pigs' intestinal microbiota were already observed by day 65 of age. Moreover, synbiotic supplementation influenced carbohydrate and amino acid metabolism, as well as the production of indole, skatole and short-chain fatty acids (SCFAs) (Zhu et al., 2022).
Factors influencing the efficacy of probiotics in swine
The efficacy of probiotics in swine is determined by a combination of biological, environmental, technological, and nutritional factors, all of which collectively shape both health and productivity outcomes. One of the key determinants of response to pro-biotic intervention is the animal's age, as it reflects the maturity and stability of the gut microbiota, as well as the susceptibility to dietary modulation. The greatest probiotic effectiveness is typically observed in weaned pigs during the periweaning period, when the natural gut microbiota undergoes substantial disruption and the intestinal barrier remains functionally immature under conditions that favour pathogen colonization and impair nutrient digestion and absorption (Pang et al., 2022).
For instance, Wang et al. (2019 a) demonstrated that supplementation with Lactobacillus fermentum and Pediococcus acidilactici improved gut health and growth performance in weaned pigs. These effects were associated with reduced systemic inflammation, modulation of intestinal micro-biota composition, increased production of short-chain fatty acids, and inhibition of potentially pathogenic bacteria, collectively indicating an improvement in intestinal function and resilience. In contrast, the effects of probiotics in sows and finishing pigs tend to be more moderate, likely due to a more stabilized microbiome and less dynamic physiological changes. Nevertheless, even in these age groups, they have been shown to improve metabolic status and enhance immune function (Balasubramanian et al., 2016; Hirata et al., 2022; Konieczka et al., 2023; Liu et al., 2025).
Another crucial factor influencing the success of probiotic therapy is the appropriate strain.. Its performance depends largely on adhesion capacity to intestinal epithelial cells, resistance to gastric acidity and bile salts, and production of antimicrobial compounds such as bacteriocins and lactic acid. Zhao et al. (2019) revealed that the effectiveness of lactic acid bacteria probiotics in the swine gastrointestinal tract is highly influenced by the bacterial species and their natural lifestyle. Lactobacillus reuteri, a species typically associated with vertebrate hosts, survived the intestinal passage in pigs more effectively than species less adapted to the host environment, such as L. casei (a nomadic bacterium) or L. fermentum (a free-living species). These findings suggest that probiotic selection should consider the strain's adaptation to the digestive environment of livestock animals. Although the overall impact of administered probiotics on the native gut microbiota was limited, the presence of reutericyclin, a compound produced by L. reuteri, exerted a subtle but significant modulatory effect on the microbiome. Notably, bacteria delivered via fermented feed persisted in the pig intestines as well as, or even better than, freeze-dried cultures, indicating that feed fermentation may serve as an effective alternative to conventional probiotic delivery methods. Therefore, prior to practical application, thorough in vitro and in vivo evaluations under target conditions are recommended to confirm strain-specific efficacy.
The effectiveness of probiotic therapy in swine depends not only on the specific strain selected, but also on the mode of administration whether as individual strains or in multistrain formulations. Studies have shown that multistrain formulations often yield stronger effects by more effectively supporting gut microbiota, enhancing intestinal barrier function, and stimulating the immune system (Jeon et al., 2024; Cao et al., 2025). However, it should be noted that a greater number of strains does not always result in better outcomes, as inter-strain reactions within a mixture may lead to competition, potentially reducing overall efficacy. Consequently, further research is necessary to elucidate synergistic or antagonistic interactions in complex probiotic supplements.
Dose and duration of supplementation are equally critical parameters. Insufficient colony-forming units (CFU) may fail to elicit biological effects, whereas excessively high doses may lead to undesirable interactions with the endogenous microbiota or induce metabolic stress (Li et al., 2012). For instance, Sun et al. (2020) reported that supplementation with Lactobacillus salivarius at doses of 0.1–0.2% significantly improved intestinal barrier integrity, reduced inflammation and oxidative stress in pigs challenged with intraperitoneal lipopolysaccharide (LPS), leading to enhanced growth and reduced diarrhoea incidence. Thus, probiotic effectiveness depends not only on dose but also on the timing and duration of administration within the production cycle.
Another important determinant modulating probiotic success is their interaction with other dietary components, especially prebiotics and acidifying additives such as organic acids. Prebiotics, including fructooligosaccharides (FOS), mannan-oligosaccharides (MOS), and β-glucans, can synergistically support probiotic survival and metabolic activity in the intestinal lumen. This combined effect, known as synbiotic action, depends on the appropriate selection of both probiotics and prebiotics to achieve optimal results (Czech et al., 2018 a, b).
Giannenas et al. (2016) demonstrated that dietary supplementation of fattening pigs with a combination of Enterococcus faecium, a prebiotic containing mannanoligosaccharides (MOS), and benzoic acid significantly improved production parameters, including growth rate and feed efficiency. Additionally, beneficial changes in the composition of the intestinal microbiota were observed, including a notable increase in the abundance of Enterococcus spp. in both the jejunum and cecum. Importantly, supplementation influenced the immunological profile of the animals; serum analysis revealed a decreased CD8+ to CD4+ lymphocyte ratio in the treated group, which may indicate a potential immunomodulatory effect of the applied feed additive combination. The authors noted, however, that no clear immune-stimulatory responses were detected, likely due to the low immunological and environmental challenge conditions of the study. However, potential antagonistic interactions among additives should be considered, for instance, highly acidifying compounds may negatively affect the viability of certain sensitive probiotic strains, especially during extended storage of feed (Marchwińska and Gwiazdowska, 2021).
The efficacy of probiotic supplementation is also strongly modulated by the form of the preparation and its route, as these factors determine microbial survival, bioavailability, and colonization capacity within the gastrointestinal ecosystem (Kim et al., 2025). The most common method for pro-biotic application in swine production is incorporation into complete feed. In this form, probiotics are usually included as components of premixes or feed additives containing carefully selected bacterial or yeast strains. These preparations are often technologically protected, for instance through microencapsulation, to safeguard microbes from high temperatures during pelleting or extrusion processes (Wang et al., 2020 a). Aerobic spore-forming strains such as Bacillus subtilis and Bacillus licheniformis are preferred for their thermal stability and enzymes' contributions to nutrient digestibility. Conversely, Enterococcus faecium is a commonly used additive in diets for weaned pigs, supporting microbiota stabilization and controlling enterotoxigenic Escherichia coli F4 (K88) colonization. Probiotics coated with biofilms or encapsulated in protective matrices are also used, as they show dramatically improved survival through the harsh gastric environment and enhanced colonization in the intestines. For example, biofilm-coated Bacillus subtilis in pigs achieved 125-fold higher oral bio-availability and 17 times greater intestinal colonization compared to uncoated forms (Wang et al., 2020 a).
An alternative and highly responsive route of administration, particularly valuable during environmental, metabolic, or immunological stress (e.g., weaning, transport, infections), is delivery via drinking water. This approach allows for rapid intervention and ensures more uniform dosing, especially when feed intake is reduced (Walsh et al., 2012). For example, administration of Lactobacillus plantarum in drinking water can reduce the load of pathogenic entero-bacteria and improve gut barrier function. Likewise, Bifidobacterium animalis-based formulations demonstrate synergistic effects when combined with electrolytes and vitamins, stabilizing water-electrolyte balance and reducing diarrhoea incidence.
A particularly targeted approach involves oral formulations (e.g., pastes, suspensions, boluses) intended for individual administration in neonatal piglets or animals at increased risk of enteric infections. During the first hours of life, piglets undergo rapid gastrointestinal colonization, and early administration of probiotics can shape the developing gut microbiota and reduce the risk of pathogen establishment (Jiang et al., 2023). Oral administration of Lacto-bacillus reuteri D8 to newborn piglets resulted in modest weight gain, attributed to improved small intestinal morphology, specifically increased villus height and crypt depth favouring enhanced nutrient absorption. This strain stimulated intestinal epithelial cell proliferation and upregulated genes involved in epithelial development, such as c-Myc and Tcf. Additionally, L. reuteri D8 enhanced mucosal immunity by increasing the number of goblet and Paneth cells and inducing the expression of defensins, lysozyme, and Muc2. It also upregulated IL-22, potentially contributing to epithelial regeneration and mucosal defence. Furthermore, increased Peyer's patch surface area and more extensive development of gut-associated lymphoid tissue (GALT) were observed, along with elevated serum IgG levels and increased expression of IL-4 and IFN-γ, indicating activation of adaptive immunity (Wang et al., 2020 b).
Another, albeit less frequent, application of probiotics involves periparturient formulations for use in sows, including topical products (e.g., aerosols, creams applied to the udder region) and systemic supplements aimed at supporting the reproductive tract microbiota and reducing the risk of vertical transmission of infections to off-spring. Some formulations contain strains that modulate uterine and vaginal mucosal immunity, though further validation under field conditions remains necessary (Feng and Liu, 2022).
Accordingly, the selection of probiotic form and administration should align with the stage of production, physiological status of the animal, nature of environmental stressors, and the biological characteristics of the probiotic strain. Microbiological compatibility is also essential, strains must exhibit acid and bile tolerance, epithelial adhesion, and competitive exclusion of pathogens. In intensive swine production systems, successful probiotic application further depends on the product's storage stability, resistance to physicochemical factors, and compatibility with other dietary components.
Conclusion
Probiotics represent a promising, sustainable strategy in modern swine nutrition, supporting gut microbial homeostasis, modulating immune function, and contributing to improved metabolic efficiency and productive performance. Their effectiveness depends on factors such as the animal's development stage, diet composition, and strain-specific properties. Although the underlying molecular mechanisms are not yet fully elucidated, ongoing research continues to strengthen their position as integral components of precision-based and welfare-oriented pig production systems.