The Thai Journal of Veterinary Medicine


One hundred eighty, male layer-type chickens with no antibodies were divided into 6 groups, 30 birds in each. Each group was vaccinated with a different strain of ND vaccine, La Sota, B1, Ulster, VG/GA and 6/10 for groups 1, 2, 3, 4 and 5, respectively. All vaccinated birds received vaccine when 5-weeks-old, by intranasal inhalation. Birds in group 6 were non-vaccinated controls. All birds were weighed when 5-, 8- and 10-weeks-old. They were challenged when 8-weeks-old with local strain of ND virus. Clinical signs and mortality rates were observed for 3 weeks. Serological responses were determined when 5-, 7-, 8-, 10- and 11-weeks-old. The results revealed that the body weight of birds in group 4, which received the VG/GA strain was the lowest when 8-weeksold. The body weight of birds in group 1, which received the La Sota strain, was the highest both before and after challenge. After challenge, the mortality rate among the vaccinated groups was not significantly different. The serological response of birds in groups 1 to 4, after vaccination, was highest at 2 weeks postvaccination (PV) and declined by 3 weeks PV. The antibody titres of birds in vaccinated groups, 3 weeks postchallenge, increased at least 18.4 times when compared to titres before challenge.

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