Examination of Salmonella prevalence and slaughter findings in pigs based on rye feeding, coarser feed structure and vaccination against Lawsonia intracellularis under field conditions.

Salmonella remains a food safety concern through pork. This field study assessed the impact of high rye diets and Lawsonia intracellularis (LI) vaccination on Salmonella seroprevalence and pathological findings at slaughter in fattening pigs. Six commercial farms participated in a three-phase trial with varying rye levels and optional immunoprophylaxis against LI. From Phase 1 to 3, rye content increased progressively (pre-, mid-, finishing phase). In Phase 1 (P1), the proportion increased from 5% to 20% to 40%. Phase 2 (P2) showed a higher inclusion level, with ≥30 to ≥40 to 60-70%. In Phase 3 (P3), rye inclusion increased from 30% to 50%, also a LI vaccination was introduced. Salmonella serology was available for four farms across all phases; slaughter data (pathological findings) for six farms in Phases 2-3. Increasing dietary rye levels (P1 to P2; P1 to P3) significantly lowered Salmonella optical density percentage (OD%), especially on farms with high baseline contamination (Farm 1: P1 13.96%, P2 2.78% P3 2.88%). In P3, a reduction in slaughter findings, particularly lung and pleural abnormalities (Farm 1-4: P2 20.54%, P3 15.19%), was observed following LI vaccination. Highest prevalence of pathological findings (lung and pleura: Farm 6: P2 60.31%, P3 66.15%) was noted without any measures. These findings highlight the value of gut health management through nutrition. High dietary rye levels appear to stabilize microbiota, strengthen the intestinal barrier and reduce Salmonella antibodies. Combining tailored feeding regimes with preventive health protocols may enhance pig resilience and improve food safety in modern swine production.