TNF and infection: In agreement with the present results, Wang et al. (15) found that neither the source (pZnO or ZnO) nor the inclusion level (pZnO at 110 or 220 mg/kg Zn or ZnO at 2,400 mg/kg Zn) affected the mRNA levels of pro-inflammatory cytokines like TNF-α, interferon gamma and interleukin-1 beta in piglets weaned without artificial infection.