Examination of the immune response induced in chickens by domestic live Newcastle disease vaccines administered under different conditions

The immune response induced by domestic authorized Newcastle Disease (ND) live vaccines was determined. The effect of administration of the vaccines under different conditions, such as in the presence of maternal antibodies and using different vaccination periods and routes, was examined. ND vaccine strains (B1, VG/GA, Clone30 and MET95) were administered to 4 day-old specific pathogen free (SPF) chickens by the oral route either by gavage or ad libitum in drinking water. After 3 weeks post inoculation (PI), there was no difference in the increase in the HI titers induced by the different ND vaccine strains. However, groups that received the ND vaccine strains ad libitum showed greater increases in HI titers than those that received the ND vaccine strains by oral gavage. The B1 strain was administered by either eye drop or ad libitum in drinking water to 4 day-old layer chickens that had maternal antibodies against the ND virus. The geometric mean (GM) of the HI titers increased more than 10-fold in all experimental groups. The HI titers in the groups that had high maternal antibody titers decreased until 4 weeks PI. Three chicken breeds (Chankey (CH), Cobb (CB) and Redbird (RB)) were inoculated with 4 ND vaccine strains by oral gavage at 3 weeks old. The GM of the HI titers increased more than 30-fold in all experimental groups at 4 weeks PI, although the HI titers in the CB group inoculated with the B1 strain were significantly lower than those in the other groups. The CH, CB and RB chickens were inoculated with the B1 strain ad libitum in drinking water. The ratio of chickens that showed more than a 5-fold increase in HI titer at 4 weeks PI was 100% in CH, 93.3% in CB and 93.3% in RB. These immune responses were better than those in the chickens that were inoculated with the B1 strain by oral gavage. These data suggest that the immune response against ND vaccines is affected by differences in vaccination route, chicken breed and the existence of maternal antibodies. Therefore, it is essential to adhere to the generally recommended vaccination programs and dosage regimen for ND vaccines.