Immunological competence of different domestic chicken breeds against avian influenza infection

In order to evaluate the impact of a selection for high laying performance on the capacity to respond to an infection with avian influenza virus (AIV), four different chicken lines were tested: A white layer as well as a brown layer breed originating from a commercial layer breeding program, and a white layer and a brown layer line maintained as a conservation flock for decades without any selection. The different chicken breeds were infected with AIV of different pathotypes (low pathogenic to high pathogenic) to evaluate and compare their immunological competence. Morbidity and mortality rates as well as viral shedding were investigated as parameters of virus infection. Identification of immune cells in blood samples collected after different time points following inoculation was determined. In general, the chickens of the two phylogenetically related brown layer lines (irrespective of the performance type) were more resistant to infection with the selected AI-viruses, reflected by a lower mortality rate (low virulent AIV) or a prolonged length of survival before succumbing to the disease (highly virulent AIV). Corresponding to these results, CD8-positive cell counts were reduced in both white layer lines. This observation was also confirmed in an in vivo allogenic transfer experiment where brown layers eliminated the transferred cells within a shorter time period. In conclusion, our results do not support the theory of reduced immunological competence of high performance layer breeds (at least against AIV infection). Instead, brown layer strains had a faster CD8-positive immune cell response after viral or allogenic stimulus than the phylogenetically distant white layers resulting in a better resistance against AIV infection.