The significantly decreased overall antibody production against formalin inactivated P. multocida vaccine in the As exposed kids as compared to the control group indicated an adverse effect of As on humoral immune response of thekids.Das (2011) also reported significantly lower lymphocyte stimulation index in goats exposed to As for 270 days. It has been suggested that As has a cytotoxic effect on the antibody producing cells as it causes necrosis and depletion of lymphoid cells in the immuno-biological organs causing immune-suppression (Biswas et al., 2000).However, supplementation of 250 IU vitamin E/kg diet ameliorated the adverse effects of As on humoral immunity as antibody titre values in group T1 and T3 were comparable. Das (2011) also reported ameliorating effect of vitamin E by improving lymphocyte stimulation index in As exposed goats. Vitamin E appears to improve the immune response by enhancing chemotaxis by increasing receptor-bound urokinase-plasminogen activator in neutrophils and production of interleukin-1 and major
histo-compatibility class II antigen expression by blood monocytes (Politis et al., 1995).