Alleviation of heat stress-induced microbial dysbiosis in pigs through dietary supplementation with vitamins and trace elements

BACKGROUND: Chronic heat stress (HS) is known to impair animal health and productivity, in part by altering gut microbiota. This study investigated how HS affects the pig gut microbiome and whether dietary supplementation with antioxidants and trace elements (vitamins E, C, selenium, and zinc) at moderate (D1) or high (D2) doses can mitigate these effects. RESULTS: During the adaptation phase, feed efficiency was similar across groups, but as the experiment progressed, the thermoneutral control improved while the heat-stressed control deteriorated. Supplemented diets (D1/D2) partially alleviated this efficiency loss. Microbiome analysis revealed that HS progressively reduced diversity, reaching the lowest Shannon index during exposure. High-dose supplementation markedly increased richness, exceeding control levels. Total microbial abundance declined under HS, with opportunistic pathogens enriched particularly during early exposure. Guild-level indices further indicated a shift under HS. Aerotolerance indices decreased (ATi: TC > D1 > D2 > HSC), reflecting hypoxia-prone conditions favoring obligate anaerobes and SCFA producers. Among supplemented groups, D1 most closely stabilized aerotolerance toward control levels, while D2 maintained an SCFA-dominant community and enhanced butyrate capacity. Genus-level correlations with qPCR-based host gene-expression markers were assessed across all groups. HSP70 was the dominant correlate, and the most extreme associations were confined to a few taxa, indicating marked group specificity. CONCLUSION: Chronic HS in pigs induced microbial dysbiosis characterized by reduced diversity, loss of beneficial SCFA producers, and expansion of opportunistic pathogens. Dietary supplementation counteracted these adverse changes in a dose-dependent manner. While moderate supplementation provided partial stabilization, high-dose supplementation more effectively restored microbial diversity and enriched beneficial taxa, making it the more effective strategy for mitigating HS-induced microbiome disruption.