Efficacy of a killed Salmonella Enterica serovar Typhimurium bacterin vaccine administration in layer birds challenged with heterologous Salmonella Enterica serovar Enteritidis

In this study, we evaluated the efficacy of administering a killed Salmonella enterica ser. Typhimurium bacterin (ST) vaccine with an adjuvant intramuscularly on humoral immunity, cellular immunity, and SE load reduction in layers. The ST vaccine was prepared with 97% S. Typhimurium and an adjuvant of 3% Immune Plus® with preservatives. Eighty 14-week-old Salmonella-free Hy-Line W-36 pullets were randomly allocated into two groups: unvaccinated control and ST vaccinated, with 40 birds per group. Birds were immunized intramuscularly with 500 µL (Endovac) vaccine at week 17 and a booster dose at week 19. At 27 weeks of age, both groups were challenged with 5 × 10⁸ CFU/mL of nalidixic acid-resistant Salmonella enterica ser. Enteritidis. At 22, 23, and 24 weeks of age, ST-vaccinated birds showed higher serum anti-Salmonella IgY levels than the control group by 186%, 202% (P < 0.05), and 2700% (P > 0.05), respectively. At 28 weeks of age, vaccinated birds had 8.3% lower levels (P > 0.05) of anti-Salmonella IgA in bile and 240% greater levels (P < 0.05) of anti-Salmonella IgY in serum compared to control group. At 28 weeks of age, splenocytes from the ST-vaccinated birds had increased antigen-specific T-lymphocyte proliferation (P > 0.05). There were no significant differences in CD4+/CD8+-T-cell ratios, IL-10, IL-4, IL-1β, IFNγ mRNA levels in the spleen and cecal tonsil between vaccinated birds compared to control. However, the vaccine did not reduce the Salmonella Enteritidis load in ceca, spleen, and liver. It can be concluded that the intramuscular administration of the killed ST vaccine with the adjuvant Immune Plus can increase serum antibody titers and induce a humoral immune response specific to Salmonella. However, the increase in serum antibody titers were not successful in reducing the Salmonella load in ceca, spleen, and liver.