Diet-vaccine interactions: SQM Iron and Salmonella vaccination shape poultry gut microbiota.

UNLABELLED: Vaccines to prevent Salmonella are rapidly gaining traction in the poultry industry. Yet how these interventions interact with other management strategies to influence the broader gut microbial community, rather than Salmonella per se, remains poorly understood. Understanding these effects is critical because shifts in the microbiome can alter nutrient metabolism, immune function, and pathogen dynamics in ways that could either enhance or suppress management strategies aimed at improving bird health and food safety. Here, we examine how a live-attenuated Salmonella vaccine (AviPro Megan Vac 1) and iron supplementation, two widely adapted management strategies, individually and jointly shape the cecal microbiome of broiler chickens. Specifically, we compare standard iron supplements (FeSO4) with a polysaccharide-complexed iron supplement (SQM Iron) which uses a complexation process that "hides" iron from Salmonella via time- and tissue-specific release of this critical nutrient. Using 16S rRNA gene sequencing, we found that while overall microbial diversity was unchanged, both interventions induced reproducible shifts in community composition, including enrichment of taxa linked to fermentation and short-chain fatty acid production. Vaccination alone promoted Bacillota genera associated with gut homeostasis, whereas iron supplementation altered competitive dynamics by reducing Streptococcus and favoring several rare taxa. Strikingly, combining these treatments suppressed several beneficial fermentative genera, and Staphylococcus was markedly increased, revealing nonadditive effects. These findings illuminate the potential of integrated strategies, combining immune stimulation with precision micronutrient supplementation, to improve poultry health and food safety. However, these results also underscore the intricate microbial trade-offs that must be carefully navigated to avoid unintended consequences in modern production systems.

IMPORTANCE: Globally, non-typhoidal Salmonella (NTS) is a persistent food safety challenge and pre-harvest control is an industry priority. While Salmonella vaccines are rapidly gaining adoption, their interactions with other common management practices such as nutritional strategies remain unclear. Iron metabolism is particularly important, as it influences host immunity, pathogen colonization, and shapes the gut microbiome. This study investigates how live-attenuated Salmonella vaccine (AviPro Megan Vac 1) and iron-based nutritional management interact to shape the cecal microbiota of broiler chickens. Specifically, we focus on SQM Iron, with a complexation process that enables time- and tissue-specific release of this critical nutrient. Our findings indicate that targeted combinations of immune stimulation and micronutrient supplementation can selectively remodel the poultry gut microbiome, with potential implications for nutrient utilization, microbial metabolism, and integrated, non-antibiotic approaches to reduce Salmonella burden while supporting flock health.