Investigation of Intestinal Health in Broiler Chickens Following Salmonella Typhimurium and Coccidiosis Vaccination and Challenge with Salmonella Typhimurium.

Salmonella enterica and coccidia (Eimeria spp.) are important intestinal pathogens in broiler production. Salmonella has high zoonotic potential, and coccidia are responsible for large economic losses. Live vaccines reduce shedding of Salmonella and minimize the impact of coccidial infections on broiler performance. This study investigated the interaction between both vaccines on the intestinal health of broilers. The 2 × 2 experimental design included vaccination against Salmonella Typhimurium (ST) (no vaccination or vaccination on day 14) and vaccination against coccidiosis (no vaccination or vaccination on day 1). On day 28, all groups were challenged with a ST marker strain resistant to nalidixic acid. Re-isolation of ST from the liver and ceca on day 42 indicated higher susceptibility to systemic infection with ST in birds vaccinated against coccidiosis than that in unvaccinated birds. On day 42, cecal immunoglobulin A (IgA) levels against ST decreased in the group vaccinated against ST and coccidia compared to those in all other groups. IgG antibodies in the cecal contents significantly decreased in the group vaccinated against coccidiosis compared to that of the group vaccinated against ST. There was no difference in systemic IgG levels among groups. Analysis of the cecal microbiota revealed a significant difference in beta diversity on days 28 and 42 between the groups vaccinated against coccidiosis and unvaccinated groups. Functional pathway profiling showed increased activity of pathways associated with carbohydrate and arachidonic acid metabolism in the group vaccinated against ST compared to that in other groups. Gene expression of claudin 1, claudin 4, E-cadherin, β-catenin, and zonula occludens 2 in the cecal wall differed between the groups on days 28 and 42. These findings indicated the significant influence of ST and coccidiosis vaccines on the intestinal health of broilers; however, further studies are required to clarify the implications for health and performance.