Ileum of laying hens supplemented with different levels and sources of copper. A, laying hen supplemented with inorganic Cu (8 mg/kg diet), B and C, denote laying hens supplemented with organic Cu (8 and 4 mg/kg diet, respectively), D and E, represent laying hen supplemented with Cu nanoparticles (8 and 4 mg/kg diet, respectively). Arrow represents reduced villi length and thickness as well as slight necrotic enteritis. Arrowhead indicates moderate lymphoid depletion.