Abstract
The infection by Salmonella Typhimurium (ST) is one of the most prevalent causative agents of lethal diseases in ducklings and represents a potential public health problem. Avoidance the duck Salmonellosis is very mandatory. So, vaccination is considered an acceptable solution to the public objections of drug residues and provides an unexpected, serious safety and it seems to be a possible practical option. For this purpose, six hundred and forty seronegative ducklings were clustered into four replicates which assigned to G1 (vaccinated by live attenuated ST vaccine at one day old age), G2 (vaccinated by inactivated ST vaccine at 15 days old age) and G3 (primed by live attenuated ST vaccine and boosted by inactivated ST vaccine after 21 days). Control unvaccinated group still without any treatment (G4). All vaccinated and control groups were challenged weekly with by virulent S. Typimurium strain with a dose 0.1 ml of 108 CFU/ml intramuscularly till 16 weeks post vaccination ( WPV ) and 13 weeks post boosting ( WPB ). The calculation of re-isolation% was done. From results, it was observed the G1 reached to satisfactory protection after 2 WPV despite, G2 reach the maximum protection at 4(WPC). Concerning the re-isolation%, it was noticed the higher re-isolation% in G1 was detected at 5WPC in contrast G2 which still having low re-isolation% till 14 WPC. The G3 was considered the best because can protect duckling from infection during the first 3WPC and very low re-isolation% till 13 WPB. It was concluded that, live attenuated ST vaccine is very important at one day old age to avoid morbidities and mortalities till 3 weeks old age. The boosting by inactivated ST vaccine after brimming by live attenuated was potentiated immune response and reduced bacterial shedding. It was recommended for subsequent booster dose by inactivated ST vaccine before egg lying to confer satisfactory maternal antibodies level for ducklings.

Key words: S. Typimurium, challenge, duck, immune response, vaccine and recovery rate