The mRNA expression levels of IL-6 in the FAdV-only group were significantly higher than those in the control group from 1 to 5 dpi with FAdV-4-HB1501 (p < 0.05), whereas the IL-6 mRNA expression level in the IBDV-FAdV co-infection group was significantly different from that in the control group at 5 dpi with FAdV-4-HB1501 (p < 0.05). The gene discussed is IL6; the disease is coinfection.