Sodium Butyrate in Pig Nutrition: Applications and Benefits

Abstract

Efficient, cost-effective and sustainable pork production remains a primary objective in modern pig farming. However, the extensive use of antibiotics in animal nutrition has raised significant concerns regarding food safety and the emergence of antibiotic-resistant bacteria. These challenges have prompted the search for safe and effective alternatives to antibiotic growth promoters. Sodium butyrate (SB), the sodium salt of butyric acid, has gained considerable attention as a functional feed additive in swine production. Its supplementation has been shown to improve intestinal morphology, regulate gut microbiota composition and enhance immune competence, resulting in better nutrient utilization and growth performance. Moreover, SB supplementation may support environmental sustainability in livestock production by mitigating the emission of harmful gases in swine housing facilities. Although current evidence is limited, in vitro studies have reported promising reductions in NH₃, H₂S and total gas production by 17.96%, 12.26% and 30.30%, respectively. Comparable effects have also been observed in laying hens, where NH₃ emissions were reduced by 26.22%. This review summarizes current knowledge on the application of SB in pig nutrition, focusing on its mechanisms of action, effects on health and productivity, and potential environmental benefits. The findings indicate that SB represents a promising and safe alternative to antibiotics, supporting both animal welfare and sustainable pork production within modern livestock systems.

1. Introduction

The growing human population and the consequent increase in nutritional demand are placing substantial pressure on food production systems, with these challenges closely intertwined with climate change [1]. As natural resources are limited, increasing agricultural output relies primarily on achieving higher yields per unit of arable land or per animal. In livestock production, improving productivity is strongly influenced by genetic selection, reproduction management, feeding strategies, and overall health status, which are hallmarks of intensive farming systems [2]. In highly concentrated production systems such as pig farming, there is rising attention to animal welfare [3], biosecurity, food safety [4] and the environmental impacts of production [5].

Conventional pig production often relies on antibiotics to manage health issues and optimize growth. Antibiotic use across all growth phases improves weight gain, reduces morbidity and mortality and offers economic benefits exceeding the cost of administration [6,7]. However, concerns have emerged regarding the widespread use of sub-therapeutic antibiotics, including antibiotic resistance [8] and the presence of residues in food products [9,10]. These risks underscore the necessity for alternative strategies, including biostimulants and feed additives that support pig health and growth without antibiotics [11]. Widely explored alternatives include probiotics, prebiotics, phytobiotics, enzymes, and acidifiers, which can also positively influence the rearing environment [12,13].

Among environmental challenges, the emission of harmful gases such as ammonia (NH₃) from intensive livestock operations poses threats to animal welfare and the environment [14]. Nutritional strategies aimed at reducing NH₃ emissions include lowering crude protein content with balanced amino acids [15], supplementation with enzymes [16,17,18], herbal products [19], probiotics [20,21] and organic acids [22,23]. Organic acids, naturally occurring in animal, plant and microbial sources, serve as energy substrates during gastrointestinal metabolism, lower gastric pH, stimulate digestive enzyme secretion, inhibit pathogens and enhance nutrient digestibility, positioning them as promising antibiotic alternatives [24,25].

The efficacy of organic acids in swine nutrition depends on multiple interacting factors, including their chemical and physical properties (e.g., consistency, odor, water solubility and corrosiveness), dosage, diet composition, animal age, health status and the intended site of action within the gastrointestinal tract (GIT) [25]. In practical feeding systems, organic acid salts are generally preferred over free acids due to their lower corrosiveness and improved handling properties, while encapsulation technologies reduce unpleasant odor and enhance feed palatability [26].

Encapsulation and microencapsulation technologies designed to protect the active compound allow for optimized inclusion rates and more consistent biological responses, thereby improving the efficiency of organic acid use in livestock diets [27,28]. Coating or microencapsulation is particularly important for achieving targeted delivery and functional activity in the distal regions of the GIT, where organic acids exert their most pronounced effects on gut health and microbial modulation [29]. These technologies involve one or multiple protective layers composed of materials such as starch or starch analogues, proteins, gums, lipids or their combinations, which release the active substance following metabolic degradation [30].

The effectiveness and durability of the coating are strongly influenced by structural characteristics, including the number and size of surface microcracks, which are critical for maintaining coating integrity during feed manufacturing processes such as thermal treatment and pelleting. Consequently, key parameters determining the performance of the final product include particle structure, processing method (e.g., spraying, spray-cooling) and the type of coating material used to protect the active component [30].

Encapsulation enables controlled release and improved bioavailability of organic acids in the distal GIT, thereby enhancing their functional efficacy. However, commercially available products vary substantially in coating quality, which can markedly influence release kinetics and animal performance outcomes. Ensuring intestinal availability of organic acids is essential as premature dissociation or absorption in the stomach may limit their effectiveness [25]. Therefore, resistance to gastric conditions combined with stability during feed processing represents a critical determinant of successful organic acid application in sustainable pig production systems.

Commonly applied organic acids in pig and poultry nutrition include lactic, formic, acetic, propionic, fumaric, citric and butyric acids, either individually as mixtures or in combination with other feed supplements [24,31]. Organic acids, when considered as a nutritional strategy, have the potential to improve health status and productive performance in pigs, depending on their individual properties or synergistic combinations [11]. They can be applied in various forms, including mixtures of different fatty acids [23,32], combinations of fatty acids with other nutritional additives [33,34], single compounds [35,36] or selected product formulations applied in targeted combinations [37].

Among organic acids, the group receiving the greatest attention as feed additives comprises the SCFA, also known as volatile fatty acids, which contain fewer than six carbon atoms [35]. SCFA exert multiple beneficial effects by improving the intestinal environment, modulating the gut microbiome, and stimulating host metabolism [38]. Their modes of action as well as those of their salts, are associated with the inhibition of pathogen growth and colonization, enhancement of digestion and nutrient absorption and positive trophic effects on the intestinal mucosa [26]. SCFA are naturally produced in the GIT as metabolic products of microbial fermentation of carbohydrates and endogenous substrates, occurring in the forestomach of polygastric animals and in the intestines of monogastric animals [39]. The principal fermentation products, accounting for up to 83%, are butyric (butyrate), acetic (acetate), and propionic (propionate) acids [40].

Butyric acid is a colorless to pale yellow, volatile and corrosive liquid with a strong, pungent odor [41], reminiscent of rancid butter, where it was first identified [40]. It represents a terminal metabolite of intestinal bacterial fermentation of complex carbohydrates by obligate anaerobic bacteria and occurs naturally at high concentrations in the lumen of the large intestine. Neutralization of butyric acid with bases or carbonates results in the formation of salts known as butyrates (e.g., sodium butyrate, calcium butyrate, magnesium butyrate), which are widely used as feed additives in pig production. The biological efficacy of these compounds is attributed to the presence of the active butyrate ion [42,43,44,45]. These characteristics make butyrates highly effective nutritional tools for supporting intestinal health and productivity in pigs.

Sodium butyrate a derivative of short-chain butyric acid, and its mechanisms of action position it as a potential alternative to antibiotic growth promoters. The literature reports diverse effects of SB related to energy metabolism, acidification and microbiome modulation, metabolic regulation, gastrointestinal histostructure, intestinal health, and growth performance in pigs. These effects have been investigated under a wide range of experimental conditions, prompting interest in SB as a biostimulant capable of enhancing animal health and productivity. The objective of the present review is to synthesize available research findings from comprehensive studies conducted by multiple research groups on organic acids, with a particular focus on SB in pigs, as reported in major scientific databases. By doing so, this article aims to highlight the efficacy of SB supplementation, its mechanisms of action and the context-specific factors determining its practical application in sustainable pig production systems.

2. Materials and Methods

2.1. Literature Search Strategy

This review was conducted using a combined systematic and narrative approach, following the PRISMA 2020 guidelines [46] to ensure transparency and reproducibility and adapted to the scope of a qualitative synthesis appropriate for agricultural sciences.

A structured literature search was performed in PubMed, Scopus and Web of Science, covering approximately the last 10–20 years prior to manuscript preparation. The search focused on studies addressing the use of SB and related organic acids in swine nutrition. Reference lists of relevant publications were additionally screened to identify further eligible studies.

Search queries were developed using Boolean operators (AND/OR) and included keywords related to SB, organic acids, swine nutrition, gut health, microbiota, growth performance, pathogen control, environmental emissions, encapsulation technologies and reproductive performance.

2.2. Eligibility Criteria and Study Selection

Studies were included if they investigated pigs at any production stage and evaluated free or protected SB, alone or in combination with other feed additives, reporting outcomes related to growth performance, gastrointestinal health, microbiota, immune responses, pathogen control, reproduction, or environmental emissions. Eligible study types included peer-reviewed experimental studies, systematic and narrative reviews and selected conference or institutional reports with sufficient methodological detail.

Studies focusing on non-porcine species, unrelated applications of organic acids or lacking relevant biological or nutritional outcomes were excluded.

Titles and abstracts were screened for relevance, followed by full-text assessment against the predefined criteria.

2.3. Data Extraction and Synthesis

From each included study, information was extracted on study design, animal category, SB formulation, dosage, intervention duration and principal outcomes. Due to heterogeneity in study designs and endpoints, meta-analysis was not performed. Instead, results were synthesized using thematic analysis and narrative integration.

Study quality was evaluated qualitatively based on peer-review status, methodological transparency and source credibility, in line with PRISMA-informed narrative review practices.

3. Sodium Butyrate as a Feed Additive in Pig Production

Sodium butyrate is the sodium salt of butyric acid, with the molecular formula C₄H₇NaO₂, molecular weight 110.09, density 1.324 g/cm³ (30 °C) and melting point 250–253 °C. It is a white crystalline substance or amorphous powder, highly soluble in water (>330 g/L) [47]. SB is widely utilized in human medicine, dietetics, and animal husbandry. In humans, research has focused on its role in intestinal homeostasis and as a potential therapeutic agent for gastrointestinal disorders [48]. Butyrate, produced by the gut microbiota through the fermentation of dietary fiber, serves as a primary energy source for colonocytes and plays a critical role in gastrointestinal health by supporting cell function, maintaining the intestinal barrier, modulating the microenvironment and reducing inflammation [49,50,51,52].

The beneficial effects of butyrate are largely attributed to its trophic function in the intestinal epithelium, where it promotes the renewal of damaged cells, regulates luminal pH, inhibits pathogenic microbes, modulates the microbiota, and improves nutrient absorption [53]. These properties, whether via endogenous microbial production or oral supplementation, support intestinal metabolism and overall health, thereby enhancing productivity.

In animal husbandry, SB is primarily used as a feed additive in intensive systems such as pig and poultry production. It represents a feasible nutritional strategy to improve feed efficiency and growth performance [54]. In pigs, butyrate promotes the proliferation and renewal of intestinal cells, improves mucosal morphology, and maintains the integrity of the intestinal wall, thereby enhancing nutrient digestion and absorption [45,55,56]. In addition, SB strengthens the intestinal barrier by suppressing inflammation and enhancing protective mechanisms [57,58]. It modulates the gut microbial balance by promoting beneficial bacteria over pathogenic species, as demonstrated under both in vitro [59] and in vivo [60] conditions and contributes to a reduction in post-weaning diarrhea and other gastrointestinal disorders [57,61].

The dual benefits of SB include improvements in animal health and productivity [62,63,64], mediated through its effects on microbial fermentation throughout the gastrointestinal tract [65], while simultaneously mitigating environmental impacts, such as the reduction in NH₃ emissions from manure as demonstrated in vitro studies [60,66].

Given its diverse product formulations and multifaceted effects on the gut microbiome, intestinal health, animal productivity, and environmental sustainability, SB offers substantial potential for application in modern pig production systems (Figure 1).

Their presentation should be aligned with current knowledge and emerging trends regarding the use of SB as a feed additive in swine nutrition, highlighting its mechanisms of action, benefits and practical applications within sustainable pig production systems.

4. Effect of Sodium Butyrate on the Intestinal Microbiome

The GIT is a complex ecosystem that critically influences animal health and productivity. The gut microbiome plays a central role in nutrient absorption, immune function, and the maintenance of intestinal homeostasis, all of which directly impact pig performance [67]. A healthy porcine gut harbors a diverse microbial population, with beneficial bacteria predominantly belonging to the Firmicutes and Bacteroidetes phyla, which together account for 85–90% of the microbial population in the GIT [68,69].

The composition and activity of the gut microbiome are dynamic and influenced by multiple factors, including diet, physiological status, substrate availability, pH, SCFA, bile acids and oxygen gradients. This spatial and temporal heterogeneity complicates direct comparisons between studies but underscores the importance of microbiome modulation as a strategy to improve pig health and growth efficiency [67,70]. Weaning represents a particularly critical period: the abrupt transition from milk to solid feed induces drastic changes in microbiota structure and it typically takes 2–3 weeks for the large intestine to restore fermentation capacity [71,72,73].

Sodium butyrate administered as a feed additive, provides an opportunity to stabilize the gut microbiome during these vulnerable periods. It can be delivered directly or indirectly by promoting butyrate-producing microbes through prebiotic or probiotic supplementation [53]. Although additional SB does not always lead to higher luminal concentrations. In an in vivo study by Biagi et al. [74] conducted in weaned piglets over a six-week period, dietary supplementation with SB at inclusion levels of 1000, 2000, or 4000 ppm did not result in significant differences among treatments with respect to gastric, jejunal, and ileal pH; NH₃ concentrations in jejunal and ileal digesta; SCFA concentrations in the jejunum and ileum; counts of lactic acid bacteria in the jejunum; or morphological parameters of intestinal mucosa samples from the jejunum, ileum, and cecum. Accordingly, SB concentrations along the intestinal tract were not increased at any of the tested doses, which led the authors to suggest a rapid metabolism of SB prior to reaching the jejunum. Similarly, Chiofalo et al. [75] reported lower butyric acid concentrations in weaned piglets receiving either spray-dried or fat-protected SB compared with control animals. However, these treatments were associated with improvements in final body weight, intestinal morphology, and lactic acid bacteria populations. These findings suggest that the observed benefits were likely mediated by synergistic interactions between dietary butyrate and lactic acid bacteria, rather than by increased luminal butyrate concentrations alone.

It can favorably modulate microbiota composition, increasing the abundance of SCFA-producing anaerobes such as Clostridium spp. and Prevotella [59,60,69]. Supplementation with probiotic strains, including Clostridium butyricum, can further enhance endogenous butyrate production and support intestinal homeostasis [21,76]. Endogenous butyrate is produced by microbial fermentation of undigested polysaccharides, oligosaccharides and disaccharides in the large intestine [43]. Fermentation yields pyruvate, acetyl-CoA and butyryl-CoA, which is converted to butyrate via two major bacterial pathways: (i) the butyryl-CoA:acetate transferase pathway, utilized by species such as Faecalibacterium prausnitzii and Roseburia and (ii) the butyrate kinase pathway, predominant in Clostridium butyricum and Coprococcus spp. [49]. Some bacteria also use fermentation end-products like acetate, lactate or succinate to produce butyrate. The rate and quantity of butyrate production depend on microbiota composition, substrate type and availability and feed composition [43].

Additional and intraluminally generated SCFA can play a pivotal role as natural selective bacteriostatic agents, bioregulators of intestinal mucosal growth and modulators of systemic energy metabolism through both direct and indirect mechanisms [26]. Key factors determining their bacteriostatic and bactericidal properties include SCFA type, inclusion level, exposure time and other contextual variables. SCFA exert direct effects on the metabolism of certain pathogenic microorganisms. In their undissociated form, they freely penetrate the semipermeable bacterial cell membrane. Once inside the bacterial cytoplasm, dissociation of the acid lowers the intracellular pH and leads to denaturation of essential enzymes [11]. The resulting protons (H⁺) and anions (RCOO⁻) are cytotoxic, disrupting bacterial membranes and selectively reducing the intestinal pathogen load [25], thereby lowering the risk of gastrointestinal disorders [77].

In parallel with its direct antimicrobial effects, butyrate exerts a pronounced influence on microbial fermentation and is capable of modulating different bacterial populations in the large intestine [65]. Butyrate shapes the intestinal microbiome depending on bacterial adaptation to variations in luminal acidity in the porcine cecum [60]. The extracellular dissociation of butyric acid into butyrate and hydrogen ions, together with increasing concentrations of acidic fermentation products, results in a reduction of luminal pH in the large intestine [43,52]. Most intestinal pathogens are sensitive to low pH, and the proliferation of pH-sensitive bacteria such as Escherichia coli, Salmonella and Clostridium perfringens is markedly reduced at pH values below 5, whereas acid-tolerant species persist [78].

Acidification of intestinal contents creates unfavorable conditions for undesirable microorganisms while simultaneously promoting the growth of beneficial, acid-tolerant bacteria such as lactobacilli. Increased populations of lactic acid bacteria and enhanced lactic acid production, together with butyrate-mediated pH reduction, further stimulate the abundance of SCFA-producing strict anaerobes (e.g., Clostridium and Prevotella). This synergistic microbial shift strengthens bacteriostatic and bactericidal effects, contributing to a further reduction in intestinal pathogen loads [69]. Similar beneficial patterns in pathogen control have been reported following SB supplementation in weaned piglets, growing pigs and finishing pigs [33,55,62,79,80].

Supplementation of SB at higher dietary concentrations does not consistently result in improved performance; however, it has demonstrated potential in reducing the shedding and dissemination of Salmonella [81,82,83]. In particular, decreased Salmonella prevalence has been reported in the lymphatic tissues and bloodstream (bacteremia) of pigs [84], indicating a possible role in limiting systemic infection.

Overall, dietary supplementation with SB has the potential to favorably modulate the intestinal microbiome in pigs. Nevertheless, its effects should be evaluated on a case-by-case basis, taking into account dose, formulation, animal category and interacting nutritional factors. While the effects of SB on animal health and productivity depend on dosage and formulation, its strategic application, particularly when combined with other feed additives and applied over appropriate supplementation periods, represents a promising nutritional approach for microbiome modulation, gut health support, disease resilience, and sustainability in pig production systems.

5. Effects of Sodium Butyrate on Intestinal Morphology

Microbial fermentation in the large intestine contributes approximately 16.4% of the total energy required for vital processes in pigs, with butyrate being one of its key metabolic products [73]. Butyrate has received particular attention as a primary energy source for colonocytes [50,85]. Absorption of butyrate and other SCFA occurs through the apical membrane of colonocytes via multiple mechanisms, including passive diffusion of the undissociated form and active transport of the dissociated form through specific SCFA transporters, such as monocarboxylate-bicarbonate and Na⁺-linked monocarboxylate transporters (MCTI and SMCTI) [52]. Once absorbed, colonocytes rapidly metabolize butyrate through β-oxidation to acetyl-CoA, which serves as a key substrate for ATP (Adenosine triphosphate) production, supporting the energy needs of rapidly proliferating cells and reducing intestinal permeability, particularly during weaning [43,54,71] (Figure 2).

Butyrate stimulates cellular renewal and differentiation in the intestinal epithelium, influencing tissue growth and proliferation mechanisms [86]. While microbial fermentation naturally produces butyrate in the large intestine, oral supplementation with feed additives such as SB can increase its availability throughout the GIT. The trophic effects of butyrate span the entire intestinal epithelium, enhancing villus height, crypt depth and goblet cell number and density, which collectively increase the absorptive surface area of the small intestine [43].

Sodium butyrate supplementation on the histological structure of the stomach and various intestinal segments in pigs have been reported in numerous studies [36,43,55,62,63,79,86]. Despite the generally favorable evidence regarding the beneficial role of butyrate, contradictory findings have also been documented, with some studies reporting no significant morphological changes following SB supplementation during the critical weaning period [56,74] or during the finishing phase [87]. The authors of these studies attributed the lack of observable effects to factors such as weaning age, additional stressors, or pre-existing health challenges.

In contrast, other investigations have highlighted the trophic effects of SB in neonatal and finishing pigs, including enhanced intestinal cell proliferation, improved mucosal morphology and increased capacity for nutrient absorption [88,89]. Although outcomes are occasionally inconsistent, the majority of available evidence indicates that SB exerts a positive influence on gastrointestinal morphology, particularly in suckling piglets, which also represent the most extensively studied animal category in this field.

Feed additives such as SB are generally most effective in young animals, where they help mitigate weaning-associated impairments in gut health, including altered intestinal morphology, microbial dysbiosis and reduced growth performance resulting from stress and immature digestive function [71,73,90,91]. From a sustainability perspective, these improvements support enhanced animal robustness, improved feed utilization and reduced reliance on therapeutic interventions, contributing to more resilient and efficient pig production systems.

Overall, the effect of SB on intestinal morphology is pronounced in early-life pigs but is highly dependent on factors such as age, physiological status, weaning practices, stress levels, diet composition and administration strategies. Careful consideration of these variables is necessary to maximize the benefits of SB supplementation in pig production.

6. Immunomodulatory Properties of Sodium Butyrate

The protective function of the intestinal mucosa is closely linked to its integrity and histological structure. In addition to its trophic effects on colonic mucosa, butyrate plays a central role in regulating intestinal homeostasis and immunity, exerting anti-inflammatory, antioxidant, anticarcinogenic and barrier-protective effects [48]. The intestinal ecosystem comprises the epithelium, immune cells, enteric neurons, microbiota and its metabolites and nutrients, all of which contribute to mucosal defense and overall gut health [52]. These components form the basis for nutritional and management strategies aimed at improving health and productivity in pigs [71]. At the mucosal level, butyrate enhances intestinal protection by reducing inflammation, mitigating oxidative stress and reinforcing the mucosal barrier [50]. Activation of mucosal mast cells is a critical factor associated with decreased barrier function, particularly in early-weaned pigs [92]. Butyrate mediates anti-inflammatory effects by inhibiting mast cell activation and suppressing the release of inflammatory mediators, including histamine, tryptase, and pro-inflammatory cytokines such as TNF-α and IL-6. These effects contribute to reduced intestinal damage, enhanced barrier integrity and improved growth performance in weaned pigs [45,55].

Sodium butyrate has also been shown to modulate humoral immunity. Supplementation in sows increases immunoglobulin A (IgA) content in colostrum, supporting better growth and health of piglets during the suckling period [44,58]. In addition, SB administration in pig feed can enhance systemic and mucosal immune responses, as evidenced by increased serum IgG and IgA concentrations in jejunal tissues [57]. Beyond immunoglobulin regulation, butyrate strengthens the intestinal barrier by enhancing tight junction integrity, stimulating mucin production and promoting antimicrobial peptide secretion, thereby providing robust protection against pathogens [52]. Studies in pigs fed with protected SB have demonstrated increased numbers of goblet and mucin-secreting cells in the ileum, resulting in improved intestinal defense and overall gut health [80].

Collectively, these findings indicate that SB not only supports intestinal morphology and nutrient absorption but also exerts profound immunomodulatory effects, enhancing the resilience of pigs to gastrointestinal challenges and contributing to improved health and productivity.

7. Significance of Sodium Butyrate in Nitrogen Metabolism and Excretion

The microbiome, one of the components characterizing intestinal homeostasis, is a functional unit related to the metabolism of nutrients and the efficiency of feed-absorbed substrates, directly affecting productivity [54,73]. During digestion, most of the available nutrients (carbohydrates, proteins, fats, minerals and vitamins) are absorbed in the small intestine, and in the large intestine continue the undigested by the enzymes components of food (crude fiber, lipids and insoluble protein) and endogenous secretions that are fermented by microorganisms [93]. This microbial fermentation process for carbohydrates (saccharolytic bacterial fermentation) occurs primarily in the proximal colon. In the distal colon, with their depletion as an energy substrate, proteins (proteolytic fermentation) are broken down with the formation of SCFA, mainly branched chain (iso-butyrate, valerate and iso-valerate) and potentially toxic NH₃ metabolites containing sulfur compounds, indoles and phenols [50,94].

Ammonia derived from protein fermentation in the gut is among the major odorous compounds contributing to unpleasant sensations in pig farms [60]. If the NH₃ content of the air in the area with animals is above the optimal values, which range between 10 and 25 ppm [95], it is irritating to the lungs and leads to health problems with negative consequences for both pigs and personnel [18,19]. NH₃ released by the livestock industry is an environmental pollutant affecting air, soil, water, biodiversity and is a prerequisite for serious local or global environmental crises [15]. The fecal load itself has a negligible contribution to directly endangering animal health and the environment, compared to the amounts excreted by the mixing of urine and the urea contained in it with fecal microorganisms containing the enzyme urease, which catalyzes hydrolysis [95]. The concentration of NH₃ and the equilibrium between its ionized (NH₄⁺) and non-ionized (NH₃) forms within livestock buildings are directly influenced by ambient temperature and manure pH. Higher temperatures and pH values above 7 promote increased NH₃ levels [96], whereas lowering manure pH shifts the equilibrium toward the ionized form, thereby significantly reducing NH₃ volatilization and emissions.

The main factors determining the quantities NH₃ are related to the housing conditions (type of floor, manure removal system and climatic conditions in the building), features characterizing the animals (physiological stage, age) and feed efficiency (composition of mixtures, phase feeding) [15,78,96,97]. They are most often taken into account when developing approaches for the correct management of N emissions from pig farms. In order to limit N losses and increase the sustainability of pork production, the efficiency of protein conversion should be maximized [98]. Effective utilization of N is economically important, due to the continuous increase in the prices of protein feed [17] and it has environmental importance, because N in food is a major cause of the high NH₃ levels in pig rearing in the conditions of modern industrial production [96].

The nutritional strategies for pigs for reducing emitted NH₃ and N are interconnected, aimed at modifying the intestinal microbiome to reduce NH₃ precursors and protein fermentation, shifting the pathway of excretion of N from urine to feces and lowering their pH. This is achieved through various models: reducing the amount of raw protein in the feeds; optimizing the protein content in combined feed, according to the specific needs; balance of the amino acids in the feed; the use of sources containing N with slow release; inclusion of fermenting carbohydrates; enzymes; food additives, aiding directly or indirectly the absorption of N-probiotics, enzymes, acidifiers, etc. [15,23,78,93,95,98].

In pig farming as feed acidifiers are used organic acids, by themselves or in combinations with each other, with predominant participation of SCFA [25]. Fermentation of undigested polysaccharides in the colon leads to acidification of the intestinal humus. As a result of the decay of the produced SCFA, the hydrogen ions emitted provoke a decrease in the pH of feces and NH₃ emissions [93]. In in vitro trials was found that organic acids (phosphoric, citric, fumaric and malic acids) had a positive influence on NH₃ emissions in the caecal fermentation of feed with carbohydrate content [22]. A similar result was reported by Upadhaya et al. [23] when feeding pigs with the addition of a protected combination of organic acids. In a study by adding 0.03% SB to pig feed was found a reduction in emissions not only of NH₃ but also of hydrogen sulphide and total gas [60]. Other studies have indicated a positive impact of SB supplementation on hydrogen sulphide emissions only [79] or total gas emissions [74] with neutral or negative impact on released NH₃.

The increase in SCFA concentration is associated with changes in the composition of the gut microbiome [67]. SB can regulate NH₃ substrates producing NH₃ and some NH₃-producing microorganisms [60]. NH₃ concentrations in the intestinal lumen can be reduced by active carbohydrate fermentation, which stimulates the bacterial need for N due to increased growth [79] and the energy provided for it by butyrate in the form of ATP. A potential solution for a mutually reinforcing effect is a reduction in crude protein in food, without limiting the amounts of N and amino acids needed for protein synthesis and to avoid compromising growth [53,94,97,99].

Ammonia is the main waste product of amino acid catabolism (deamination), detoxified in the liver by urea synthesis. Most of it is excreted in the urine, but the ability in pigs to use a mechanism to convert it into amino acids for protein synthesis for the host is an option for N utilization [100]. The available amounts of urea in the blood are a key source of N for bacterial proliferation in the colon [93]. SB supplementation was found to have a beneficial influence in suckling pigs by reducing urea concentration in blood without affecting other hematological parameters [62]. Fang et al. [57] presented results of the use of SB in weanling pigs, which showed lower serum concentrations of urea N, cortisol, D-lactic acid, diamine oxidase, and higher for glucose and triglycerides with which the authors connect the more efficient N utilization. The concentration of urea in manure is highly dependent on protein nutrition and can be altered by changing the protein content of the diet [93].

Current evidence provides heterogeneous indications regarding the effects on harmful gas emissions, with available knowledge suggesting modest positive trends primarily based on in vitro studies. The lack of more comprehensive in vivo experiments limits clear interpretation of these findings. Therefore, additional well-controlled in vivo studies are required to elucidate the magnitude, underlying mechanisms and consistency of these effects under different production conditions.

8. Use of Sodium Butyrate to Mitigate Post-Weaning Stress Syndrome (PWS)

Protein fermentation in the large intestine selectively influences the gut microbiota and its metabolites, which may compromise epithelial integrity and predispose piglets to gastrointestinal disorders [93]. The intestinal microbiota interacts in a complex manner with the gut environment, and imbalances between these components can alter fermentative activity and microbial ecology, thereby favoring pathogen proliferation, infectious diseases and diarrhea [94]. Weaning represents a critical developmental stage for piglets and is frequently associated with growth retardation due to impaired nutrient utilization, resulting from changes in gastrointestinal morphology, microbiota composition and digestive function in an immature gut [18,93]. These effects arise from the combined impact of multiple stressors, including establishment of social hierarchies, environmental changes, and the transition from sow’s milk to solid feed, all of which can negatively affect growth performance and overall health status [71].

Intestinal dysfunction during this sensitive period leads to substantial economic losses in pig production, particularly when weaning occurs at or before 21 days of age [11,57,92]. Early post-weaning challenges, including disrupted gut microbiota, delayed mucosal adaptation, and reduced nutrient absorption, are collectively described as PWS [53]. Elevated gastric pH in weaned piglets further compromises digestive efficiency and can be partially mitigated through dietary inclusion of organic acids [25].

Antibiotic growth promoters (AGPs) and pharmacological zinc oxide (ZnO) have been widely used to control enteric pathogens and improve growth performance in pigs; however, their application is increasingly restricted due to antimicrobial resistance, regu- latory limitations and environmental concerns [6,7,8,9,10,11]. While AGPs act through direct antimicrobial mechanisms [6,8] and ZnO provides broad-spectrum anti-diarrheal effects during the post-weaning period [9,11], ZnO use has been linked to heavy metal accumulation and environmental pollution, leading to its gradual phase-out [9,10].

In contrast, SB, particularly in protected or microencapsulated forms, supports gut health through indirect mechanisms, including modulation of microbial fermentation, reinforcement of intestinal barrier function, and attenuation of inflammatory signaling pathways [23,24,25,43,45,52]. Coated SB has been shown to improve growth performance, gut morphology and diarrhea control in antibiotic-reduced systems [30,42,74,79], while promoting beneficial microbiota and suppressing pathogens [59]. Importantly, SB does not contribute to antimicrobial resistance or heavy metal accumulation [60,66] (

Table 1. Benchmarking Sodium Butyrate Against Antibiotics and Zinc Oxide.

Metric	Antibiotics (AGPs)	Zinc Oxide (ZnO)	Sodium Butyrate (Coated)
Antimicrobial Activity	Direct bacteriostatic/ bactericidal [6,8]	Broad-spectrum at pharmacological doses [9,10]	Indirect via pH, membranes, microbiota [24,25,45]
Inflammation Control	Low [6]	Moderate [11]	High via NF-κB inhibition [45,52]
Gut Morphology	Improved but variable [6,11]	Improved villus height [11]	Consistent villus/crypt improvement [42,74,79]
Diarrhea Reduction	Strong [6,11]	Strong [11]	Moderate–strong (coated forms) [23,79]
Regulatory Restrictions	Severe global restrictions [7,8]	Phasing out in many regions [9,10]	Acceptable in all markets [12,13]
Environmental Impact	Antibiotic resistance risk [8]	Heavy metal residues [9]	Environmentally benign [60,66]
Performance Outcomes	Strong [6]	Strong [11]	Moderate–strong, delivery dependent [23,79]

).

Dietary supplementation with organic acids, particularly SB, has shown promising potential to alleviate PWS and reduce reliance on antimicrobial interventions [53]. During this vulnerable period, SB has been reported to improve growth performance, modulate gut microbiota composition, increase SCFA concentrations, and support intestinal mucosal development [75]. Numerous studies confirm its beneficial effects in weaned piglets [56,57,61].

For optimal efficacy, SB should be delivered in a form that ensures gradual release throughout the gastrointestinal tract, with effective delivery to the large intestine achieved via microencapsulation within a lipid matrix [43]. Butyrate can fully exert its beneficial effects on gut health only when targeted delivery to functionally relevant intestinal regions is achieved. Jia et al. [28] compared non-protected acidifiers (susceptible to buffering and early absorption) with encapsulated forms and demonstrated that encapsulation resulted in greater pH reduction, increased Lactobacillus populations, reduced Escherichia coli counts, improved villus height-to-crypt depth ratios, and enhanced growth performance in weaned piglets.

Because SCFA are readily absorbed [77], protective microencapsulation of butyrate is applied to prevent premature dissociation and absorption in the upper gastrointestinal tract [88]. This secondary technological processing, applied after pelleting, slows the rapid degradation of bioactive compounds in the proximal gut and enables their gradual release along the intestinal tract. Most commercial butyrate salts are coated with a protective fat matrix, typically hydrogenated palm oil, ensuring that the majority of butyrate is released only after enzymatic degradation of the lipid coating by pancreatic lipase [75]. During intestinal absorption, gradual digestion of the lipid coating facilitates effective delivery of butyrate to the large intestine. The superior efficacy of microencapsulated compared with free SB has also been demonstrated by Chiofalo et al. [75].

Based on available evidence, SB, particularly in microencapsulated form, can be effectively applied as a nutritional strategy to support piglets during the weaning period. Feed additives generally exert the greatest effects in young animals, where improvements in growth performance and reductions in neonatal mortality have been reported [68]. Although the response to SB supplementation during this critical life stage may vary, the majority of studies indicate beneficial effects on weaning-related challenges, with protected and microencapsulated formulations being preferable to uncoated powder forms.

From a sustainability perspective, such strategies contribute to enhanced animal resilience, improved feed efficiency and reduced dependence on antimicrobial inputs, supporting more robust and sustainable pig production systems.

9. Effect of Sodium Butyrate Supplementation on Productive Traits in Pigs

Economic benefits in pig production largely depends on the reproductive performance of sows and the growth and feed conversion efficiency of pigs during the fattening period. Maximizing growth rate while minimizing feed consumption remains a central objective for swine producers. In this context, dietary supplementation with sodium SB has been investigated as a nutritional strategy to enhance productivity across different physiological stages in pigs.

In sows, the inclusion of SB during the final stage of gestation has been associated with improved reproductive outcomes and subsequent piglet performance during lactation. Studies have reported a reduced proportion of gilts failing to conceive and higher piglet growth rates during lactation following SB supplementation, effects that were attributed in part to enhanced colostrum and milk quality [44,101].

Most research on SB has focused on its use during the critical post-weaning period, which is associated with substantial physiological and metabolic challenges. Consistent with its role in mitigating weaning-associated stress, SB supplementation has been linked to improved growth performance in weaned pigs. Positive responses were reported when SB was added at 0.45 kg/t feed in piglets weaned at 28 days [45] and at 1.0 kg/t feed in piglets weaned earlier, at 21 days of age [55]. Similar improvements in growth performance have also been observed in older and fattening pigs [63,87,88]. Positive effects have also been reported in finishing pigs supplemented with protected SB, with several studies documenting beneficial outcomes [32,69,79,82]. However, these effects are not consistently observed across all investigations, as some studies have reported neutral responses even at higher inclusion levels (2.0–4.0 kg/t feed) [74], or no measurable effects on intestinal morphology, growth performance, or meat quality [87] (

Table 2. Comparison of Free vs. Coated (Protected) Sodium Butyrate.

Feature	Free Sodium Butyrate	Coated/Microencapsulated Sodium Butyrate
Odor/Palatability	Low [27,75]	High and controlled release [30,75]
Gastric Stability	Rapid dissociation in stomach; most butyrate absorbed early [27,42]	Protected from gastric acidity; coating resists early release [30,42]
Primary Release Site	Stomach and proximal duodenum [27,56]	Jejunum, ileum, and cecum depending on coating matrix
Bioavailability at Distal Intestine	Low [27,56]	High and controlled release [42,79]
Mode of Action	Mainly systemic and gastric effects [43,48]	Local action on epithelial cells, microbiota, and immune tissues [43,45]
Effects on Gut Morphology	Inconsistent due to limited intestinal exposure [27,56]	Consistent villus height increase and crypt-depth normalization [42,74,79]
Microbiota Modulation	Limited; minimal SCFA-driven shifts in distal regions	Promotes beneficial microbes, suppresses pathogens [59,69]
Anti-inflammatory Impact	Modest [48,51]	Strong NF-κB inhibition, cytokine regulation [45,52]
Commercial Application	Cost effective but less targeted [26]	Higher cost but more predictable biological outcomes [30,75]

).

The odor of pure butyric acid is generally perceived as unpleasant by humans, resembling aged cheese or rancid butter; however, given the very low dietary inclusion rates used in pig feeding, this characteristic is unlikely to adversely affect feed intake and may even stimulate consumption. An effective approach to mitigate odor-related concerns is the microencapsulation of butyrate within a protective matrix, which also represents a key technological advantage of protected formulations.

Results regarding its influence on average daily feed intake (ADFI) remain inconsistent. While some studies demonstrated increased ADFI in fattening pigs fed SB-supplemented diets [87], others reported no significant effects on ADFI in weaned pigs [36,57,102], even at inclusion rates up to 2.0 kg SB/t feed [103]. Similarly, Walia et al. [81] observed no changes in ADFI, growth, or feed conversion ratio in pigs fed diets containing 3.0 kg SB/t. In contrast, Sun et al. [63] reported that dietary supplementation with 0.2% SB increased final body weight.

Unfortunately, the considerable variability and lack of consistency among reported results across studies make direct comparisons difficult. This variability is largely attributable to differences in diet composition, SB dosage, feed formulation, animal age, intestinal maturity, duration of supplementation and experimental conditions [79]. These factors highlight the importance of context-specific optimization of SB inclusion levels, as dosage alone is not the sole determinant of response. Achieving consistent improvements in pig growth performance and feed conversion efficiency requires careful consideration of these interacting variables.

10. Impact of SB on Pork Meat Quality

The use of functional feed additives that enhance growth performance and nutrient utilization in pigs can have consequential effects on meat quality. Intensive growth rates are frequently associated with increased deposition of intramuscular fat, which contributes to improved flavor, juiciness, and tenderness of pork [104]. In this context, SB supplementation has been investigated for its potential to modulate muscle development and lipid metabolism, thereby influencing the overall sensory and technological properties of pork.

Zhang et al. [105] reported that dietary inclusion of SB improved intramuscular fat content, muscle marbling, post mortem muscle pH (pH_24h), and meat tenderness, suggesting a beneficial effect on pork quality traits. Similarly, Sun et al. [63] observed enhanced carcass characteristics in finishing pigs supplemented with SB. In contrast, Morel et al. [87] found no significant differences in key meat quality parameters between control and SB-fed pigs, indicating that the response to SB supplementation may vary depending on production conditions and experimental design (

Table 3. Mechanisms of Influence on pork meat quality through the application of Sodium Butyrate.

Meat Quality Trait	Mechanistic Pathway Influenced by Butyrate
Fat Deposition	Upregulation of lipogenic genes (FASN, ACC, SREBP-1); HDAC inhibition alters lipid metabolism [38,104,105]
Tenderness	Reduced inflammatory catabolism; improved mitochondrial efficiency [43,87]
Water-Holding Capacity	Enhanced antioxidant activity (SOD, GPx) reduces protein oxidation; improved cellular integrity [20,88]
Oxidative Stability	Increased endogenous antioxidant enzymes; reduced ROS formation [36,38]
Color Stability	Improved mitochondrial metabolism and reduced lipid oxidation [87,88]

).

Although, SB demonstrates promising potential for improving both growth and meat quality traits, findings across studies remain inconsistent. The variability may be attributed to differences in SB dosage, duration of supplementation, animal age, genetic background, and feeding phase. Furthermore, environmental and management factors, such as housing conditions, feed formulation, and animal health status, may influence the degree of responsiveness to SB supplementation.

In general, current evidence suggests that SB can contribute to improved pork quality under specific conditions, particularly by promoting favorable muscle characteristics and lipid deposition. However, further well-controlled studies are needed to elucidate the mechanisms by which SB affects muscle metabolism and to establish optimal inclusion levels and feeding strategies for consistent improvements in pork quality.

11. Cost-Effectiveness of SB Feed Additive

Economic evaluation is a crucial component in determining the feasibility of using feed additives such as SB in commercial pig production. Although numerous studies have demonstrated the biological and physiological benefits of SB supplementation, including improved gut health, nutrient absorption, and growth performance, its practical application must also be supported by comprehensive cost–benefit analyses. Feed costs account for the majority of total production expenses in pig farming; therefore, any additive must demonstrate economic viability in addition to animal breeding efficacy.

The financial implications of SB supplementation vary depending on production conditions, dosage, formulation, and category of pigs. Lynch et al. [83] reported that the inclusion of SB in diets for growing pigs increased overall feeding costs, primarily due to the higher price of butyrate-enriched feed formulations. In contrast, Galfi and Bokori [62] reported a favorable economic balance in pigs supplemented with SB, characterized by a 9% reduction in feed costs and a 13% increase in return from pig sales. These outcomes were associated with improved profitability and enhanced fattening performance, particularly in terms of growth rate and feed conversion efficiency. Such contrasting findings highlight the importance of optimizing both the form and inclusion rate of SB to achieve cost-effectiveness.

Upadhaya et al. [79] suggested that cost reduction and improved profitability could be achieved through the use of microencapsulated SB, which allows for gradual release along the GIT. This technology enhances the additive’s bioavailability and efficacy, thereby reducing the required dosage without compromising performance benefits. By minimizing waste and improving intestinal health, encapsulated SB formulations may offer a more sustainable and economically viable strategy for commercial application.

Comprehensive financial assessments, considering both the additive cost and the potential improvements in feed efficiency, growth rate, and health status, are therefore essential for large-scale adoption. Further research should focus on developing standardized economic models tailored to different production systems and pig categories to provide clear guidelines on the cost-effectiveness of SB supplementation under diverse farming conditions.

12. Future Research Perspectives

12.1. Optimization of Dosage, Formulation, and Inclusion Strategies

Future studies should aim to optimize SB dosage, which currently ranges widely from 0.015% to 7 kg/t, as well as its delivery form (free, blended, or protected) and inclusion strategies across different age groups. Assessing bioavailability and cost-effectiveness is essential to ensure practical, economically viable applications.

12.2. Mechanistic Insights into Gut Microbiome Modulation

Research should investigate SB’s effects on the intestinal microbiome using advanced omics approaches. Particular focus should be on its impact on SCFA-producing bacteria and potential synergistic interactions with probiotics such as Clostridium butyricum. Understanding these mechanisms will enhance strategies for promoting gut health and overall performance.

12.3. Age-Dependent Responses and Immunomodulatory Effects

Further investigation is warranted into the age-specific effects of SB, critical windows for trophic and immunoregulatory responses, as well as maternal and transgenerational influences on reproductive performance. Studies should evaluate SB’s immunomodulatory roles, including anti-inflammatory activity, cytokine regulation, stress modulation and effects on systemic immunity, oxidative stress, and immune-competent cells.

12.4. Mitigation of Environmental Impact

The potential of SB to reduce N and NH₃ emissions should be validated in vivo, considering interactions between diet composition (crude protein, rapidly fermentable carbohydrates, enzymes) and microbial N pathways. This will provide reliable evidence for its role in sustainable pig production.

12.5. Impacts on Meat Quality and Production Efficiency

Future research should explore SB’s effects on growth, feed efficiency, meat quality, lipid metabolism, muscle morphology and post-slaughter muscle biochemistry under varying dietary and stress conditions.

12.6. Economic Feasibility and Sustainability

Studies should incorporate economic analyses of SB supplementation, weighing costs against productivity gains. Integrating mechanistic insights with financial assessment will support practical adoption by producers.

13. Conclusions

This review highlights SB as a multifunctional feed additive with significant potential to support gut health, animal performance and environmental sustainability in pig production systems. Unlike antibiotic growth promoters and pharmacological zinc oxide, SB exerts its effects predominantly through indirect and host-mediated mechanisms, including modulation of microbial fermentation, enhancement of intestinal barrier integrity, and regulation of inflammatory responses. These properties contribute to improved growth performance and intestinal resilience, particularly during physiologically challenging periods such as weaning.

A consistent conclusion across the analyzed studies is that the efficacy of SB is strongly influenced by its formulation and site of release within the gastrointestinal tract. Free butyrate salts are rapidly absorbed in the proximal gut, which may limit their effectiveness, whereas protected and microencapsulated formulations enable targeted delivery to the distal intestine, resulting in more consistent improvements in gut morphology, microbial balance, and productive outcomes. This formulation-dependent response explains much of the variability reported in the literature and should be carefully considered when comparing SB with conventional antimicrobials.

From a sustainability perspective, SB represents a regulatory-compliant alternative that does not contribute to antimicrobial resistance or heavy metal accumulation and has demonstrated potential to reduce N losses and NH₃ emissions under specific conditions. Overall, SB, particularly in protected formulations, offers a viable nutritional strategy for improving animal health and performance while supporting the transition toward more sustainable and antibiotic-reduced pig production systems. Further well-controlled in vivo studies are warranted to optimize inclusion strategies and validate its long-term benefits across diverse production conditions.