2.6 Histopathology
Tissue samples (brain, thymus, trachea, lungs, heart, kidneys, pancreas, gut, cecal tonsil and liver) were fixed in formalin. After 48 hrs, the fixed tissues samples were embedded in paraffin, sectioned, stained with H & E and were examined for microscopic lesions as described previously (Neufield et al., 2009).