Salmonella vaccination studies in breeders and their progeny
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Salmonella are ubiquitous enteric bacteria and potential pathogens, some affecting a wide host species range. Eradication of poultry-specific Salmonella from commercial flocks resulted in increased prevalence of serovars with a wider host range in poultry and consequently increased potential of human food-borne disease due to consumption of poultry products. Regulatory Hazard Analysis Critical Control Points has been implemented with the goal of reducing Salmonella prevalence in poultry meat. Management intervention strategies to curb the occurrence of Salmonella have begun to look at competitive exclusion, killed and live Salmonella vaccines during production. Our studies focused on establishing how combined vaccination programs protect breeders through rearing and production, and if maternal antibody and competitive exclusion is protective for the progeny. Antibody response was measured at the systemic and mucosal humoral level and an infection model established to relate antibody response to actual bacterial prevalence. Day-of-age breeder vaccination increased intestinal IgG at 3 but not 10 weeks of age. Crop IgA and IgG, as well as gut and serum IgG peaks were observed after killed vaccines delivered at 11 and 17 weeks of age. An approximate 0.8 Log reduction in Salmonella counts due to live 1 and 21-day vaccine applications were obtained at 3 and 6, but not 11 weeks of age. By week 22 all vaccination programs reduced Salmonella counts by approximately 1.3 Log. High maternal antibody throughout production passed to the progeny failed to reduce Salmonella counts, whereas competitive exclusion consistently reduced Salmonella counts by approximately 1.4 Log. Maternal intestinal IgG transferred to the progeny was observed up to 13 days, but no interference of maternal antibody on the effectiveness of day-of-age live vaccination was detected. Day-of-age live vaccine reduced Salmonella counts at 3 and 13 but not 34 days of age, indicating that more than one live vaccine is necessary for prolonged protection during rearing. Live vaccine protection is probably a combined effect of humoral, cell-mediated intestinal immunity, and a competitive exclusion effect. Competitive exclusion and vaccination programs will reduce but not eliminate the incidence of Salmonella, and therefore should constitute complementary and not substitutive tools to integral biosecurity programs.