Open Access journalInfectious bursal disease is a disease of economic importance worldwide. The vaccination is an important management tool to control the disease. However, outbreaks do occur in vaccinated flocks due to vaccination failure. The selection and breeding for disease resistance may be a sustainable approach to control the disease in future. The outbreak of IBD is a threat to the emerging poultry industry in the country. Such outbreaks have not reported in native chickens so far. Therefore, this study aimed to assess the immunological tolerance of Bhutanese native chicken from a recent IBD outbreak areas in Tsirang district, Bhutan. The mortality rates in commercial and native birds maintained under same farms were assessed. Further, the level of antibody titres to IBDV of an exclusive commercial and native chicken farm from the vicinity of outbreak using commercial kit (this statement appears incomplete). Overall, the study groups consisted of commercial affected (CA), native chicken in co-existing in commercial affected (NA), Commercial Not Affected farm (CNA) and Native not affected farm (NNA). The mortality rates commercial chicken ranged from 24 to 50 percent while no mortalities were observed in native chickens in IBD affected farms. All of the four groups were seropositive to IBD virus although prevalence was significantly (p<0.05) lower in NNA group compared to CA and CNA groups. The log10 titres used to determine protective antibody titre levels showed no significant differences among the groups. Overall, the absence of clinical signs and mortality, seropositiveness to IBD virus infection and levels of protective antibody titres in unvaccinated NA and NNA groups suggests of potential immunological tolerance of Bhutanese native chicken to IBD virus infection. A further study is recommended to validate the current findings possibly through experimental infection.Jigme Dorji, Tshering Dorji, Tshewang, Tashi Y. Dorji, and Sangay Tenzin, and R. B. Gurun
