Maternal antibodies in chicks from hens vaccinated with three types of inactivated Salmonella Enteritidis vaccines

Chicks hatched from hens vaccinated with three inactivated Salmonella Enteritidis (SE) vaccine (A and B: oil adjuvant vaccine. C: aluminum gel adjuvant vaccine) commercially available in Japan were examined for fluctuations in maternal antibodies for one week after hatching and then challenged with SE. Two sets of the same breed of laying hens of different ages were used. Hens in one set were vaccinated subcutaneously in the shoulder with A at 28 and 32 weeks of age, with B at 32 weeks of age, or intramuscularly in the thigh with C at 28 and 32 weeks of age. Hens in the other set were vaccinated subcutaneously in the shoulder with A at 8 and 12 weeks of age or with B at 12 weeks of age. All vaccinations were scheduled so that the last inoculations were given on the same day in each set of hens. Fertilized eggs were collected three times : at one and two months after the last immunization from the laying hens vaccinated with A, B or C (the former set), and once at one year after the last immunization from the laying hens vaccinated with A or B (the latter set). The chicks hatched from these eggs were examined. Throughout the three tests, the chickens were grouped according to the vaccine given to them (A, B, and C groups/the first and the second tests, A and B groups/the third test, 20 chicks in each group). Blood samples were collected every day from 0 to 7 days of age, and ELISA measurements were carried out. In all tests, the average titers for maternal antibodies in all groups of chickens from vaccinated hens reached a peak at two to four days after hatching and decreased afterwards. All of the chickens demonstrated positive values at the peak. The average titers for maternal antibodies in the chicks hatched from hens that were one or two months post vaccination were clearly higher in the A group than in the B or C group from 0 to 7 days of age. However, in chicks hatched from hens which were one year post vaccination, no difference in antibody titer was observed between A and B groups, Next, challenge experiments were carried out against groups of chicks which were the sisters hatched on the same day as those used for the maternal antibodies test and a control group of chicks from un-vaccinated laying hens. In Test I, 10(2) CFU of rifampicin-resistant SE-ZK 2ax strain/0.2 ml/chick were inoculated orally in the group of chicks hatched from hens which were 1 month post vaccination and in the control group of chicks (20 chicks/group). In Test II, the group of chicks hatched from hens two months post vaccination, the control group, and the group of chicks hatched from hens one year post vaccination with A or B vaccine were orally challenged with the same SE. In addition, two challenge experiments (III, IV) similar to those described above were carried out using chicks hatched from two sets of breeder hens of broiler chickens of different ages which were vaccinated with the three kinds of vaccines in the same way as the laying hens. In Tests I, II and III, the number of SE isolated from the contents of the cecum was significantly lower for groups hatched from vaccinated hens than for the control group, but this number was far greater than the number of inoculated SE. The number of isolated SE from the contents of the cecum and the liver of chicks hatched from vaccinated laying hens was lower in group A, than in group B or C, however no such trend was observed for the broiler chickens. Maternal antibodies from hens vaccinated with killed SE vaccines were transmitted to the chicks and retained there for a long time, but these maternal antibodies did not play an important role in the prevention of colonization against SE in the cecum.