Effect of Zinc Toxicity on Lymphoid Organs in Chickens

The experiment was conducted with the objective of studies on effects of zinc toxicity on lymphoid organs by the methods of experimental pathology and flow cytometry (FCM). 200 one-day-old Avian broilers were divided into four groups randomly, and fed on diets as follows: controls (Zn 100 mg kg-1)and zinc toxic (Zn 1 500 mg kg-1, zinc toxic group Ⅰ; Zn 2 000 mg kg-1, zinc toxic groupⅡ; Zn 2 500 mg kg-1, zinc toxic group Ⅲ) for seven weeks. The weight and growth index of the thymus, spleen and bursa of Fabricius were reduced in both zinc toxic groupⅡand zinc toxic group Ⅲ when compared with those of control group. The G0/G1 phase of the cell cycles of the lymphoid organs was higher, and S, G2+M phases lower in zinc toxic groups Ⅱand Ⅲ than in control group. Lymphocytes were depleted and degenerate in the lymphoid organs. The reticular cells of the bursa of Fabricius proliferated and the reticular cells of the thymus were also degenerate and necrotic, particularly in zinc toxic groups Ⅱand Ⅲ. The results demonstrated that more than 1 500 mg kg-1 impaired the progression of lymphocytes from the G0/Gl phase to S phase obviously, inhibited the development of lymphoid organs and caused marked pathological changes in the lymphoid organs. Potential mechanisms underlying these observations are also discussed.