CUTANEOUS LESIONS IN BROILER-CHICKENS SPONTANEOUSLY AFFECTED WITH MAREKS-DISEASE

A total of 91 8- to 9-week-old broiler chickens with Marek's disease ( MD) skin tumours (''skin leukosis''), collected from 15 farms at the p rocessing plants, were examined pathologically. Grossly, the skin lesi ons comprised various sizes and numbers of feather follicular nodules, which tended to fuse with each other as their size increased. Histolo gically, the lesions were classified into five types: type A was small lymphoid cell aggregates (LCA) consisting mostly of small lymphocytes with a few lymphoblasts and very rare mitotic figures; type B had lar ge LCA consisting mainly of small lymphocytes with considerable number s of lymphoblasts and very rare mitotic figures; type C was characteri zed by large coalesced LCA consisting almost equally of small lymphocy tes and lymphoblasts with infrequent mitotic figures; type D exhibited very large coalesced LCA consisting mainly of lymphoblasts with some small lymphocytes and occasional mitotic figures; type E had very larg e coalesced LCA consisting almost completely of lymphoblasts with freq uent mitotic figures. The histological MD cutaneous lesions were relat ed to the size of gross skin nodules, the small feather follicular nod ules consisted mainly of types B and C with type A, whereas large fuse d feather follicular nodules were composed mainly of types D and E. Nu clear inclusions were frequently found in the feather follicular epith elium in all skin nodules except for the largest fused ones. MD viscer al lesions were more pronounced in birds having marked skin leukotic l esions. Feather pulp lesions (FPL) were more related to the visceral t han the skin lesions; the constituent cells of FPL were compatible wit h those of the former lesions.