Studies on the development of pelleted Newcastle disease virus (NDV) vaccine

White leghorn chickens (7-10 weeks old) were orally infused with varied doses of lentogenic and mesogenic strains of Newcastle disease virus. The antibody response of the chickens was monitored by haemagglutination inhibition tests weekly for 4 weeks postinfusion. A high dose of virus (10(9) EID50) was necessary to induce a serological response typical of chickens that resist challenge. Sera from chickens infused with low doses (10(5) EID50) of the virus only showed marginal haemagglutination inhibiting activity. Trypsin levels as high as 0.35 mg ml-1 were detected from duodenal secretions and are assumed to be responsible in part for viral inactivation. Fasting (no food and water) the chickens beyond 12 h did not appear to increase antibody response to low titre virus.