Laboratory evaluation of the immune response of young broiler chickens vaccinated against Newcastle disease under field conditions.
Four experiments were conducted to examine the efficiency of 4 different Newcastle disease (ND) field vaccination programs. For all experiments young broiler chickens were obtained from breeder flocks regularly vaccinated against ND. The following vaccination programs were tested: 1) vaccination at 1 day of age; 2) vaccination at 1 and 20 days of age; 3) vaccination at 7 days, and 4) vaccination at 12 days of age. In all experiments, 10 randomly chosen birds from each of 6 farms that were commercially vaccinated plus 10 nonvaccinated control birds were bled just prior to vaccination and the farms separated into 2 groups based on the birds' mean NDV hemagglutination-inhibition (HI) titers. At various times after vaccination, sera from 10 different birds from each of the 6 farms and 10 nonvaccinated birds were assayed for HI titers and then challenged with virulent NDV to establish disease resistance. Serologic and challenge data indicated that the majority of chickens from any one of the 4 vaccination programs produced measurable HI titers and were refractory to challenge. However, the greatest serologic response and best resistance to clinical ND were found in birds with relatively low levels of maternal immunity at the time of initial vaccination and in birds receiving a booster vaccination at 20 days of age.
D000367:Age Factors; D000818:Animals; D002645:Chickens / Q000276:immunology*; D006385:Hemagglutination Inhibition Tests; D009521:Newcastle Disease / Q000276:immunology*; D009522:Newcastle disease virus / Q000276:immunology*; D013045:Species Specificity; D014765:Viral Vaccines / Q000276:immunology*
D014765:Viral Vaccines