Monitoring And Assessment Of Immune Efficacy And Egg-laying Performance Against Avian Infectious Bronchitis

Infectious bronchitis(IB) is an acute infectious and highly contagious pathogenic disease in chickens caused by avian infectious bronchitis virus(IBV), which could infect any chicken at any age. IB mainly invade chicken respiratory, digestive, urogenital and reproductive tract, causing tremendous economic losses in the chicken industry. Currently, vaccination is the most effective method of preventing IBV infectious diseases. However, due to the many IBV serotype and the continual emergence of antigenic variants, and there is no or only a few of cross-protective immunity between the various serotypes, immunization procedures are also different. The IBV specific-antibody titers of parent stock in the seven chicken farms located in Shandong province is detected in this study. Meanwhile, the virus isolation, identification and production performance of laying hens were carried out in the suspected IBV infection chickens. Based on this, the purpose of this study is to monitor the effectiveness of the company’s current immunization programs and to provide a valuable advice for the adjustment of the immune process. The experimental results were as follows:1. According to the current immunization program, the IBV antibody levels in serum were measured by ELISA method. The IBV antibody levels in the fourth chicken farm were significantly higher than the others farms at 4 weeks of age(p<0.01). The IBV antibody levels of all chicken farms were significant increase at 16 weeks of age. However, the IBV antibody levels decreased obviously among the five of chicken farms at 19-21 weeks of age. The IBV antibody levels in the fourth chicken farm were significantly higher than the others farms at 26 weeks of age(p<0.05). At 30 weeks of age, the IBV antibody levels in the fifth chicken farm were significantly higher than those of the others farms(p<0.05). Overall, the best immune effect was the sixth and seventh chicken farms, and the fourth and fifth chicken farms were the worst.2. The tracheal tissues were collected from the thirth, fourth and fifth chicken farms, respectively. After the passage in chicken embryos and virus RNA extraction, the IBV S1 gene was amplified and identified using RT-PCR. The results of agarose gel electrophoresis showed that all of the three farms were positive reaction. Meanwhile, the S1 gene sequencing amplified by RT-PCR were completely consistent between the fourth and fifth chicken farms. Due to weak signal, sequencing of the thirth chicken farms failed. Compared the nucleotide sequence with that of the QX-Like strains in Genbank, we found that the homology was more than 97%. Genetic phylogenetic tree analysis further revealed that the IBV strains of the fourth and fifth chicken farms belonged to the QX-Like strain.3. Both of laying rate and hatchable egg rate were obviously declined in the fourth and fifth chicken farms compared with those of the sixth chicken farms, and the rate of double yellow eggs, soft-shell eggs rate, broken egg rate and malformed egg rate increased. Therefore, QX-Like strains could significant influence the egg-laying performance, which results in decreased egg production, increase the number of malformed eggs, up-regulated hatchable egg rate and egg quality.