The Thai Journal of Veterinary Medicine


One hundred, 1 week old, female broiler chickens were divided into 5 groups, 20 chickens in each. Each group was vaccinated with a different strain of infectious bronchitis vaccine; Ma5, H120 and a local strain produced by the Department of Livestock Development for groups 3, 4 and 5, respectively. All the vaccinated chickens received intraocular vaccine at 1 week old. The chickens in groups 1 and 2 served as a negative control and a positive control group, respectively. All the chickens were weighed at 1, 4 and 6 weeks old and challenged at 4 weeks old with nephropathogenic infectious bronchitis virus isolate THA001. Clinical signs and mortality rates were observed for 2 weeks post-challenge. Serological responses were determined at 1, 2, 3, 4, 5 and 6 weeks old. The results revealed that the body weight of chickens among the vaccinated groups was not significantly different (p>0.05) both before and after challenge but the body weight of chickens in the vaccinated group was significantly higher than the chickens in the positive control group (p<0.05). After challenge, the mortality rate of the chickens in groups 3, 4 and 5 was significantly lower than that of the positive control group (p<0.05). The serological response of chickens in the vaccinated groups at 2 weeks post-challenge was significantly higher than that of the positive control group (p<0.05).

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