Abstract: [Objective] To understand the prevalence and genotypic characteristics of infectious bronchitis virus （IBV） in chickens in Yanggu County, Liaocheng City, Shandong Province. [Method] 266 disease samples were collected from 27 chicken farms in four townships with large breeding volume in Yanggu County from 2022 to 2023. RT-qPCR was applied to detect IBV, and then the S1 gene sequences of some positive samples were amplified using RT-PCR to analyze the genotypes and genetic variation. [Result] The study found that IBV infection was present in chicken farms in all four townships. Forty-two IBV nucleic acid-positive samples were detected from 266 diseased samples, and the positive rate of farms and positive rate of samples were 51.85% （14/27） and 15.79% （42/266）, respectively. Among the samples from large-scale egg farms, large-scale broiler farms and free-range chicken farms, the highest positive rate and sample positivity rate were found in free-range chicken farms, which were 57.14% （8/14） and 21.30% （23/108）, respectively. Spring and winter samples had higher IBV detection rates of 24.53% （26/106） and 12.05% （10/83）, respectively. The highest positivity rate of 33.75% （27/80） was found in samples from chickens below 1 month of age. The S1 gene sequences of the seven IBV-positive samples were amplified, sequenced and analyzed, and it was found that five belonged to the GI-19 lineage and two to the GI-22 lineage. [Conclusion] There is an epidemic of IBV in Yanggu County, and spring and winter are the high infection periods. The risk of infection was higher in flocks under 1 month of age and free-range flocks, and GI-19 as well as GI-22 were the dominant lineages of IBV in this area.

Key words: infectious bronchitis virus in chickens, prevalence characteristics, S1 gene, genotypes