Article Sharing | Host-Microbiota Interactions in Domestic Pigs: The Roles of Prebiotics and Probiotics

Article Sharing | Host-Microbiota Interactions in Domestic Pigs: The Roles of Prebiotics and Probiotics

Probiotics (a group of microorganisms that confer benefits to the host when administered in adequate amounts) can correct imbalances in the gastrointestinal tract (GIT) microbiota and improve overall health in both humans and animals. The introduction of these beneficial microbes helps restore and strengthen the population of symbiotic microorganisms in the gut, thereby enhancing animals' resistance to diseases. Additionally, probiotics improve the digestion, absorption, and utilization of nutrients, leading to better production performance. However, the positive effects of probiotics on animals are strain-dependent. One study reported that after administering probiotics to weaned piglets, the count of Lactobacillus in the GIT increased, while the counts of Clostridium, Escherichia coli, and Enterobacteriaceae decreased.

Lactobacillus, as a member of the Firmicutes phylum, is a facultative anaerobic or microaerophilic bacterium capable of effectively enhancing animal feed conversion efficiency. The lactic acid it metabolically produces can inhibit the growth of harmful bacteria such as E. coli and Enterobacter. Studies have shown that using a composite preparation of Lactobacillus johnsonii and Lactobacillus mucosae isolated from healthy pig feces can significantly reduce the population of potential intestinal pathogens like Clostridium and E. coli, thereby improving gut health.

Similar effects were observed when compound lactic acid bacteria (such as Enterococcus faecalis 6H2, Lactobacillus acidophilus C3, Pediococcus pentosaceus D7, Lactobacillus plantarum 1K8, and Lactobacillus pentosus 3K2) were added to the feed of weaned piglets. Furthermore, the wild-type strain of Lactobacillus salivarius UCC118 significantly reduced the number of spirochetes in the gastrointestinal tract of pigs and influenced Gram-negative bacterial communities through its bacteriocin Abp118, despite the bacteriocin having no direct effect on such bacteria in vitro. This suggests that the strain may regulate the microbial composition in pigs through mechanisms partially dependent on bacteriocins.

Another probiotic strain, Lactobacillus reuteri, can alter the abundance of bacterial groups such as Enterobacteriaceae (including E. coli). The reuterin produced by this strain increases the abundance of two strict anaerobes within the Firmicutes phylum and inhibits the colonization of enterotoxigenic E. coli (ETEC) without disrupting the primary composition of the fecal microbiota. These findings highlight the critical role of strain specificity in probiotics for regulating animal gut microecology and health.

Probiotics added to the diet of weaned piglets can compete with pathogenic bacteria for nutrients, leading to the competitive exclusion of harmful bacterial strains. The inclusion of specific probiotics, namely Lactobacillus casei, Lactobacillus lactis, and Lactobacillus acidophilus, during the lactation period, followed by the supplementation of both probiotics and prebiotics in the post-weaning diet of piglets, significantly enhances growth rate and weight gain. Higher Lactobacillus counts and lower E. coli counts were also observed in the feces of these animals. Additionally, anaerobic bacteria such as Eubacterium, Fusobacterium, and Propionibacterium were predominantly detected between days 13 and 16 after birth in piglets, with an increase in the diversity of anaerobic bacteria noted. This is attributed to the introduction of milk replacer starting from day 14. The same study also found changes in the intestinal microbiota after the initiation of a weaning diet from day 35 post-birth. Prebiotics (compounds found in food that stimulate the growth/activity of beneficial microorganisms) have been shown to promote the growth of specific symbiotic gastrointestinal microbial populations. These microorganisms subsequently produce substantial amounts of metabolites, among which short-chain fatty acids (SCFAs) enter the colon through diffusion, low-affinity transport mechanisms (e.g., HCO₃⁻/SCFA exchange), medium-affinity transport mechanisms involving monocarboxylate transporter 1 (MCT1), or high-affinity transport mediated by sodium-coupled monocarboxylate transporter 1 (SMCT1 or SLC5A8). The production of interleukins also increases following the supplementation of prebiotics or a combination of probiotics and prebiotics (known as synbiotics) in pig diets. Furthermore, the addition of lactulose (a prebiotic) to the diet of weaned piglets enhances the immunoglobulin G (IgG) antibody response as well as serum total immunoglobulin M (IgM) and immunoglobulin A (IgA) levels. Lactose, a primary sugar in milk, acts as a prebiotic and can stimulate the development of a highly diverse microbiota in the gastrointestinal tract of growing animals prenatally. While the mechanisms by which lactulose and other prebiotics influence the immune system are not yet fully understood, it is hypothesized that they may function indirectly by altering the resident microbiota of the gastrointestinal tract and inducing changes in microbial metabolite production.