Early weaning is a critical management strategy in modern intensive pig production, employed to enhance operational efficiency through all-in/all-out systems, improve sow reproductive performance, increase farrowing room turnover, and facilitate disease control (1). However, this practice increases piglets’ susceptibility to environmental, psychological, and nutritional stressors, potentially disrupting intestinal microbiota homeostasis and impairing mucosal barrier development (2). Consequently, piglets often exhibit reduced feed intake, compromised digestibility, diarrheal disease, and in severe cases, increased mortality. In order to mitigate weaning stress in piglets, antibiotics such as colistin sulfate and chlortetracycline have been widely used as feed additives in China due to their efficacy in promoting growth and antibacterial activity (3, 4). The indiscriminate use of these antibiotics has led to drug resistance and antibiotic residues in animal products, posing risks to human health and the environment (5). In response, China implemented a comprehensive ban on antibiotic growth promoters (AGP) in animal feed in 2020 (6). This regulatory shift marks the entry of the animal production industry into a new stage and highlights an urgent need for safe, effective, and environmentally sustainable alternative strategies.

Organic acids (OA) have been widely employed in animal nutrition for decades as alternative or supplementary strategy to AGP, primarily owing to their high efficacy, environmental friendliness, and notable antibacterial activity (7, 8). Our previous studies have also demonstrated that OA can effectively reduce the intestinal pathogenic bacterial load in weaned piglets, improve gut barrier function and microbial balance, thereby alleviating diarrhea and growth retardation caused by weaning stress (9, 10). Among various OA, medium-chain fatty acids (MCFA) demonstrate distinct advantages due to their broader antimicrobial spectrum, stronger antibacterial properties, and ability to provide rapid energy (11–13). Moreover, MCFA contribute to intestinal mucosal development, enhancement of barrier function, and immune regulation (13, 14), making them particularly suitable for application during the weaning phase. However, the practical application of MCFA is often limited by their strong odor and rapid absorption in the foregut, which impair feed palatability and reduce their effectiveness. A previous study reported that dietary inclusion of blended MCFA decreased feed intake and average daily gain (ADG) in weaned pigs compared with a control group (15). Microencapsulation technology offers a solution by effectively masking the undesirable odor of MCFAs and enabling their targeted release in the distal intestine, thereby allowing more precise modulation of the hindgut microbiota and improved gut health (16). Supporting this approach, a prior study demonstrated that a microencapsulated eucalyptus MCFA product, used as an alternative to zinc oxide and antibiotics in weaned pigs, enhanced growth performance and gut health (17).

With new microencapsulation technologies for MCFA now being scaled for production, this study therefore aims to investigate the effects of microencapsulated MCFA including caprylic acid (C8:0) and capric acid (C10:0) on the gut microbiota across various intestinal segments, and its subsequent impacts on growth performance, gut microbiota community, and immune response in weaned piglets.

The experimental protocol for this study was reviewed and approved by the Institutional Animal Care and Use Committee of China Agricultural University (CAU AW51015202-1-02, Beijing, China). The experiment was performed at the Fengning Swine Research Unit of China Agricultural University (Hebei, China). The microencapsulated organic acids (MOA) used in the trial were supplied by Palmco Biotechnology Co., Ltd. (Tianjin, China), with caprylic acid (C8:0) and capric acid (C10:0) as the active constituents, together comprising 50% of the product. Briefly, a method for preparing a MOA microcapsule powder: (1) add MOA to a carbohydrate-emulsified aqueous solution and perform high-speed emulsification and shearing at a shear rate of 1,500 r/min-3,500 r/min, with the solution temperature in the tank maintained at 45 °C–70 °C; (2) homogenize the emulsified solution using a high-pressure homogenizer at a pressure of 10 MPa–40 MPa; (3) spray dry under conditions of inlet air temperature of 180 °C–220 °C and outlet air temperature of 70 °C–150 °C; (4) finally, dehumidify and dry, then collect the powder after sieving with a vibrating screen to obtain the MOA microcapsule powder.

Weaning is a critical phase in pig production, characterized by multiple stressors such as abrupt dietary change, physiologically and immunologically immature systems, and environmental transitions (2). A common consequence is a pronounced post-weaning reduction in feed intake, often leading to malnutrition and impaired growth rates. Dietary supplementation with MCFA, either individually or as blends, has been demonstrated to effectively mitigate these adverse effects (21). Existing research indicates that the growth-promoting efficacy of MCFA is influenced by their specific composition and inclusion level. For instance, Gebhardt et al. (22) observed that increasing the inclusion of an MCFA blend to 1.5% linearly enhanced both ADG and ADFI, while 0.5% caprylic acid alone also significantly increased ADG. Similarly, positive effects on ADG and ADFI have been reported with supplementation of a caprylic and capric acid mixture up to 2%, or a blend of caproic, caprylic and capric acid at 1.0% (23). A dose-dependent effect was further highlighted in a study where 0.55% of a combination of caproic and caprylic acids increased ADG in the first 2 weeks post-weaning, while a lower dose of 0.32% showed no significant effect (24). Research by Zentek et al. (25) showed that a 0.15% inclusion of non-encapsulated caprylic and capric acids did not improve growth performance. Notably, the present study demonstrated that microencapsulation of the same acid mixture at an identical inclusion level (0.15%) significantly increased both ADG and ADFI. These results suggest that the microencapsulation technology may enhance the bioavailability and biological efficacy of MCFA. In this study, although the overall ADFI increased, the ADG did not show a corresponding improvement. This suggests that the additional energy intake may have been preferentially utilized for enhancing intestinal development and immune function. Consequently, under the current experimental conditions, dietary supplementation with MOA could lead to an elevated feed cost per unit of weight gain.

Beyond growth performance, another major challenge during the weaning phase is the high incidence of diarrhea, and the application of MCFA also demonstrates significant potential in this regard. Our findings indicate that the microencapsulated MCFA blend exerts potent anti-diarrheal effects. This result is consistent with previous research reporting that dietary supplementation with 0.5% caproic acid or caprylic acid significantly reduced fecal scores in weaned piglets (26). Furthermore, in piglets challenged with Escherichia coli k88, the inclusion of 0.2% OA mixtures containing caprylic and capric acids has been demonstrated to effectively reduce the diarrhea incidence (27). Dietary supplementation with MCFA lowers the gastrointestinal pH, which enhances proteolytic enzyme activity and protein digestibility, while reducing protein fermentation in the hindgut. The resultant acidic milieu also helps inhibit the proliferation of pathogenic bacteria and optimizes the structure of the gut microbiota (7, 8). Through these mechanisms that collectively contribute to superior digestive efficiency and gut health, MCFA are effective in improving growth performance and reducing diarrhea incidence in weaned piglets. Additionally, as piglets gain body weight, intestinal maturation and microbial development progress, strengthening their resilience to environmental and pathogenic challenges (28). This largely explains the virtual absence of diarrhea observed in phase 3.

The integrity of the intestinal mucosal barrier is pivotal for preventing diarrhea, as its impairment and the consequent increase in permeability can result in substantial fluid and electrolyte efflux into the intestinal lumen, thereby inducing or exacerbating diarrhea (29). Serum DAO activity and D-lactate concentration serve as reliable biomarkers for evaluating intestinal permeability and mucosal barrier function (30). In this study, dietary supplementation with the microencapsulated MCFA blend significantly reduced serum DAO activity, whereas AGP supplementation resulted in intermediate or similar responses, with DAO values comparable to the MCFA group but not significantly different from the control group. This result aligns with the improved intestinal morphology observed in the MOA group compared to the AGP group, suggesting a stronger protective effect of MCFA on intestinal mucosal barrier function. This advantage is further supported by previous findings showing that a blend of caproic and caprylic acid glycerides more effectively improved intestinal morphology in lipopolysaccharide-challenged piglets than AGP (31). MCFA can help maintain the intestinal morphological integrity by directly supplying energy to enterocytes (14, 32). They also stimulate goblet cell proliferation and mucus secretion, which blocks the translocation of bacterial endotoxins and toxic macromolecules, preventing the reduction of tight junction protein expression, and maintaining mucosal barrier health (19, 30, 31). The lower serum IL-2 level observed in the MCFA group reflects a reduced state of systemic T-cell activation (33). This is likely attributable to the enhanced intestinal mucosal barrier, which limited the translocation of gut-derived antigens into circulation and thus diminished the persistent antigenic drive for IL-2 production.

Dietary MCFA supplementation also protected intestinal barrier integrity by suppressing pro-inflammatory factors, as evidenced by markedly reduced levels of TNF-α and IL-6 in both the jejunum and colon. This finding aligns with previous studies reporting that dietary medium-chain glycerides markedly reduced ileal IL-6 and serum TNF-α levels in weaned pigs (19, 30). Similar suppressive effects of MCFA and monoglycerides on pro-inflammatory cytokines have also been documented in sow, mice and broilers (34–36). The anti-inflammatory properties of MCFA are primarily mediated through the modulation of key signaling pathways. Specifically, MCFA and their monoglycerides downregulated the expression of toll-like receptor 4 (TLR4) and nucleotide-binding oligomerization domain protein 1, thereby inhibiting the activation of nuclear factor-κB (NF-κB) and subsequently reducing the production of TNF-α and IL-6 (36, 37). Certain MCFA, such as capric acid, have been shown to alleviate inflammatory responses and oxidative stress by directly suppressing mitogen-activated protein kinases phosphorylation and blocking NF-κB nuclear translocation (38, 39). Additionally, the higher T-AOC observed in the MCFA-supplemented group compared to the AGP group may also contribute to the anti-inflammatory effects, as excessive free radicals are known to activate the NF-κB signaling pathway (40). In line with this, Kong et al. (41) demonstrated that medium-chain glycerides increased T-AOC and SOD activity in serum and jejunum, accompanied by attenuated inflammatory responses and downregulation of the TLR4/NF-κB pathway.

The intestinal microbiota plays a vital role in nutrient digestion and absorption, intestinal epithelial development, and immune function in piglets (42, 43). A stable and diverse microbial community is fundamental to intestinal health and contributes to improved growth performance (44, 45). In the present study, dietary supplementation with microencapsulated MCFA did not affect the α-diversity of the jejunal microbiota and only led to significant enrichment of a limited number of bacterial taxa, including Prevotellaceae_NK3B31_group, Family_XIII_UCG-001, Parabacteroides, and Microvirga. These findings suggest that MCFA exert minimal influence on the overall microbial structure in the proximal gut. In contrast, more pronounced microbial shifts were observed in the hindgut following MCFA supplementation. Specifically, the colon of the MOA group exhibited numerically higher microbial richness (Ace and Sobs indices) and a greater number of differentially abundant taxa compared to the jejunum. Among these were several beneficial bacteria, such as Alloprevotella, Roseburia, Shuttleworthia, and Monoglobus, as well as certain members of Rikenellaceae and Muribaculaceae. This intestinal segment-specific response supports the hypothesis that microencapsulated MCFA function as a targeted, slow-release system, primarily regulating the distal gut where microbial density and fermentation activity are higher (13).

Consistent with our results, Li et al. (46) reported that piglets fed OA blends containing MCFA exhibited higher microbial diversity and richness in the colon compared to the AGP group. Similarly, research in sows has shown that AGP disrupted gut microbiota and decreased diversity, while MCFA supplementation promoted microbial diversity (34). The differential effects observed between the MOA and AGP groups likely stem from their distinct modes of action: AGP generally simplify the microbial community through broad spectrum inhibition, whereas MCFA help maintain a more complex and stable microbial ecosystem. This difference was clearly reflected in our study. The AGP group exhibited a microbial profile that was distinct, yet less diverse and composed of fewer dominant taxa including enrichment of Erysipelotrichales, a taxon associated with inflammation-related disorders in the gut (47). Conversely, the MOA group not only promoted greater microbial diversity but also enriched a broader range of beneficial bacteria in the colon, such as Rikenellaceae_RC9_gut_group, Alloprevotella, Monoglobus, Roseburia, Shuttleworthia and Muribaculaceae. These genera are known for their ability to degrade complex polysaccharides and produce SCFA (48–53), which correlated with the elevated colonic SCFA levels observed in our study. In the jejunum, lactate concentration was significantly higher in the MOA group and constituted the majority of total SCFA. This is noteworthy as it suggests a fermentative shift in the small intestine, which may carry important physiological and microbial implications. The increased jejunal lactate and butyrate concentrations may be associated with the elevated abundance of norank_f__Erysipelotrichaceae, as members of this family have been reported to produce both lactate and butyrate (54). The enrichment of Prevotellaceae_NK3B31_group may support butyrate production by providing succinate as a metabolic substrate for butyrate-producing bacteria (55). As the primary energy substrate for colonocytes, butyrate enhances intestinal barrier function and exerts anti-inflammatory effects (56). Collectively, the enrichment of SCFA producing bacteria in the MOA group indicates an enhanced fermentative capacity and suggests a potentially improved gut health status compared to the AGP group.

Dietary supplementation with 0.15% microencapsulated MCFA promoted feed intake, optimized intestinal microbiota composition and metabolism, and alleviated intestinal inflammation in weaned piglets. As a potential antibiotic alternative, microencapsulated MCFA demonstrate distinct advantages in modulating microbial ecology and providing long-term anti-inflammatory benefits.