Assessment of maternal immunity against Salmonella enterica serovar Heidelberg in progeny of broiler breeders vaccinated with different formulations of bacterins

Salmonella Heidelberg (SH) has been reported in broiler flocks of many countries. The ability of some SH strains of poultry origin to cause foodborne infections in humans is a concern. Usually, infection of broiler flocks by SH occurs in the first days of life. Therefore, control measures should start early post-hatch. One of the strategies is to generate high titres of anti-Salmonella IgY in breeders by using bacterins to provide passive immunity to their progeny. In this study, three broiler breeder flocks were submitted to three Salmonella vaccination regimes (two doses of vaccine 1, two doses of vaccine 2, and non-vaccinated). When breeders were 30 or 55 weeks old, some of their offspring were separated and challenged with an SH strain at 3 days of age. Dissemination to organs, caecal colonization, and faecal excretion of SH were evaluated over a period of 20 days. Chicks from vaccinated 30-week-old breeders presented lower amounts of SH in caecal contents at 1, 3, and 6 days post-infection, correlating with high titres of maternal anti-Salmonella IgY in their yolk. In contrast, there were no differences in counts of SH in caecal contents of chicks when their parents were 55 weeks old and titres of IgY were reduced. Amounts of SH in liver and spleen were low and there were no differences among birds throughout the experiment. Progeny from a 30-week-old flock vaccinated with vaccine 1 also showed lower SH faecal shedding than the remaining birds. Apparently, the maternal IgY was associated with reduction in intestinal infection by SH.