Immunological tolerance of Bhutanese native chicken to Infectious Bursal Disease Virus infection

Infectious bursal disease is a disease of economic importance worldwide. Vaccination is the only the effective method to control the disease. The selection and breeding for disease resistance is an emerging concept towards a sustainable alternative for control the disease in future. Individual chicken types/breeds are claimed to be relatively more resistant to diseases than others. The disease resistance trait and genetic resources are crucial for the development of IBD resistant breeds. The outbreak of IBD is a threat to the emerging commercial layer industry in Bhutan. However, no outbreak of IBD is reported in Bhutanese native chickens till date . Therefore, this study assessed the tolerance of Bhutanese native chicken to IBD infection through analysis of mortality rates and serum antibody titres of chicken from IBD outbreak areas in Tsirang district, Bhutan. The average mortality rates was 35.4 percent (commercial strains) and zero (native types) respectively in native chickens in IBD affected farms. All four study groups tested positive to IBD virus with 94.7, 95.2, 80.0 and 63.6 percent for CA, CNA, NA and NNA groups respectively. The number of seroprevalence of NNA was significantly (p<0.05) lower than CA and CNA groups. The log10 titres indicating protective antibody levels were not significantly different among the groups. Overall, the absence of clinical signs and no mortalities in native chicken, sero-positivity to IBD virus infection and similar levels of protective antibody titres of native chicken groups to commercial chicken line is suggestive of potential immunological tolerance of Bhutanese native chicken to IBD virus infection.