Safety and efficacy of Salmonella gallinarum 9R vaccine in young laying chickens

Salmonella enterica subsp. enterica serovar Gallinarum (S. gallinarum) is the agent of fowl typhoid, and the 9R vaccine is a commercially available, live vaccine for the prevention of fowl typhoid. The aim of this study was to assess the safety and efficacy of the 9R vaccine in young chickens. The mean weights of 5-week-old chickens vaccinated with one and 10 doses at 2 weeks old were 450.3 +/- 33.83 g and 446.8 +/- 35.68 g, respectively, which were statistically lower (P<0.05) than the mean weight (475.5 +/- 44.17 g) of the control group. Using the same procedure, the mean weights of chickens vaccinated with one and 10 doses at the age of 4 and 6 weeks were 721.3 +/- 64.03 g and 723.7 +/- 63.92 g, and 1114.2 +/- 92.21 g and 1078.27 +/- 68.93 g, respectively. Compared with the mean weights (725.7 +/- 49.50 g and 1104.3 +/- 92.34 g, respectively) of the control groups, there was no difference in terms of statistical significance (P<0.05). In addition, all vaccinated birds showed no clinical signs and survived the time course of the experiment. When all chickens were challenged with the wild-type S. gallinarum 21 days after one-dose vaccination, the mortalities between the vaccinated group and the control group were 0% to 5% and 95% to 100%, respectively. In addition, the control group demonstrated a 95% to 100% re-isolation rate of the challenge strain in internal organs and the caecum, while in the vaccinated group only a 1% to 60% re-isolation rate was observed. In this study, we showed that adjusting the minimum vaccination age of the 9R vaccine to 4 weeks is acceptable considering the safety and efficacy of the vaccine.