Seeder Model Challenge of Emerging Salmonella Infantis in Broilers: Potential of Organic Acid-Based Feed Additive in Performance and Gut Health

<i>Salmonella</i> Infantis is a recognized antimicrobial resistance threat, and in the compromised chicken gut, this pathogen penetrates weakened tight junctions, disrupts the microbiota balance, and triggers inflammation. This study evaluated the potential effects of a feed additive blend comprising short chain fatty acids including coated sodium and calcium butyrate, medium chain fatty acids, and phenolic compounds on broiler gut health and performance under a <i>Salmonella</i> challenge using a proprietary seeder model methodology. The foundation, led by a preliminary study as Part A, comprises a negative control and two treatment groups, ran to develop a seeder model, and 1056 day-old Ross 308 broiler chicks were allocated into three groups. On days 5-6, <i>Salmonella</i> Infantis 7570 was inducted via seeders in T2 (frozen strain) and T3 (live strain), while T1 remained unchallenged. No significant difference in infection development was observed between T2 and T3 (<i>p</i> > 0.05). In T1, <i>Salmonella</i> positivity checked via real time polymerase chain reaction (iQ-check II Biorad) remained below 50% at respective time points, indicating that complete isolation in the same room is not feasible. Henceforth, in the main experiment, Part B, 396 male day-old Ross 308 birds were randomly assigned to two further treatments: (1) a positive control group fed a commercial diet, and (2) a treatment group fed the same diet supplemented with 2.5 kg/t of an organic acid-based additive blend (Presan FY, Tilburg, The Netherlands) until day 28. On days 5 and 6, five birds per pen were orally inoculated with 10⁹ CFU/mL <i>Salmonella</i> Infantis 7570 obtained via Part A and placed as seeders in both treatments. A borderline tendency for lower <i>Salmonella</i> counts was observed in the treatment group on day 19 (<i>p</i> = 0.062). The control group had significantly higher lesion scores on day 13 (<i>p</i> = 0.0068), with no significant difference on day 19. Body weight was significantly higher in the treatment group on days 11 and 28 (<i>p</i> = 0.0157), with no difference on day 39 (<i>p</i> = 0.1857). Average daily gain improved significantly between days 11 and 28 (<i>p</i> = 0.0234), and feed intake was also significantly higher during this period (<i>p</i> = 0.0007). Feed conversion ratio showed a tendency to improve between days 5 and 11 (<i>p</i> = 0.0638). Overall, this study reveals that the seeder model can be adopted in <i>Salmonella</i> research, and the application of a blend showed a borderline tendency to reduce <i>Salmonella</i> counts, however significantly lower the lesion scores, thereby improving gut health in broilers under a <i>Salmonella</i> challenge.