Independent of C. jejuni-infection and feeding strategy, C. jejuni-free layers showed significant higher IL-6 mRNA expression levels only at 1 dpi, as well as IL-8 mRNA expression levels at both 1 and 7 dpi compared to C. jejuni-free broilers (Fig. 4), indicating a breed effect (p < 0.05). The gene discussed is CXCL8; the disease is infection.