Review: A systematic review on the use and effects of postbiotics on the general health, gut health, and performance of sows and piglets

Growing concerns over antibiotic resistance have led to restrictions on antimicrobial use in various regions, including the European Union, prompting the search for alternative strategies to promote gut health. Of these, postbiotics have emerged as a promising strategy due to their potential immunomodulatory, anti-inflammatory, and gut barrier-enhancing properties. Despite extensive research regarding human health, the application of postbiotics in swine nutrition remains unexplored, with limited and inconclusive findings. The definition of postbiotics has evolved, leading to inconsistencies in the literature regarding their classification and functional properties. This review aimed to clarify the concept, the definition, and classification, and evaluate the types and effects of postbiotic supplementation on the health and performance of pigs. A literature search was conducted using PubMed, Google Scholar, Web of Science, and Scopus, employing search terms mainly related to "postbiotic preparation" (i.e., cell wall fragments, exopolysaccharides, etc.) and "pig category" (gestating and lactating sows, suckling and post-weaning pigs). The search yielded 2 151 articles (published between 1982 and 2025), and 33 fulfilled the eligibility criteria (studies on swine and studies in which the postbiotic respected the latest definition of the International Scientific Association for Probiotics and Prebiotics). The findings indicate that postbiotics derived from Saccharomyces cerevisiae and Lactobacillus species are the most extensively investigated. Based on the explored studies, the mechanisms of action of the various postbiotics appear to be closely linked to their specific bioactive components and, consequently, to the originating microbial strains. Postbiotics derived from both Saccharomyces cerevisiae and Lactobacillus demonstrated beneficial effects on gut health pillars in both sows and piglets. Sows' supplementation enhanced immunoglobulin concentrations in blood (31%) and milk (58%) while reducing oxidative stress markers (malondialdehyde, 34%). In weaned pigs, postbiotic supplementation reduced pro-inflammatory cytokines (Tumour Necrosis Factor-α, Interleukin 1β and Interleukin 6) along with improvements in gut morphology parameters and α-diversity. These effects collectively contribute to improved overall health and growth performance in the animals. In conclusion, postbiotic supplementation, whether administered to sows or directly to pigs, appears to support and enhance piglet health and growth, even under challenging conditions. The limited characterisation of the postbiotic formulation employed in the studies precluded definitive attribution of the observed mechanisms of action to specific bioactive constituents. Future research should focus on defining the optimal dosage and timing of supplementation to exploit the potential benefits of postbiotics fully.