Purpose: To evaluate the efficacy of attenuated and inactivated vaccines, alone or in combination, administered by various routes, for reduction of colonization of layer hens by Salmonella.
Methods: Live, attenuated (Bioproperties Vaxsafe ST) and inactivated (Intervet) vaccines against Salmonella were administered, alone or in combination, using four different vaccination regimes, to Hyline brown-egg-laying chickens. Vaccines were applied up to 18 weeks of age. The birds were challenged with Salmonella Typhimurium, S. Infantis or S. Virchow at ~ 108 colony forming units (CFU) per bird of at 10, 16 and 22 weeks of age. Three weeks after challenge, the birds were euthanized and their ceca cultured for salmonellae. A protective index was determined by comparing populations in vaccinated and control birds. Blood was collected and titres against S. Typhimurium were determined using an ELISA.
Results: Protection was demonstrated against S. Typhimurium and S. Infantis by both vaccines with some protection afforded against S. Virchow by some vaccine combinations. The best overall protection was delivered by the combination of subcutaneous injection of the live vaccine at six weeks followed by an intramuscular injection of the inactivated vaccine at 12 weeks of age. Vaccination induced an antibody response that was stronger following two vaccinations. It was concluded that there was an association between high antibody level and protection against Salmonella colonization.
Significance: The results suggest that use of inactivated and attenuated vaccines, particularly in combination, will be useful in an integrated management strategy for control of Salmonella in poultry production.