Pathology of lymphoid organs in chickens fed a diet deficient in zinc

An experiment was conducted, including flow cytometry, to study the pathology of the lymphoid organs and peripheral blood T lymphocytes in zinc (Zn)-deficient chickens. One hundred 1-day-old broiler chickens were randomly divided into two groups and fed on diets with 100 mg/kg Zn (controls) or Zn-deficient diets (Zn, 23.63 mg/kg) for 7 weeks. The weight and growth index of the bursa of Fabricius, thymus and spleen were significantly reduced (P<0.05 or P<0.01) in Zn-deficient birds when compared with those of control broilers. The G0/G1 phase of the cell cycle of the bursa, thymus and spleen was much higher (P<0.01), and the S, G2+M phases and proliferating index lower (P<0.05 or P<0.01) in Zn-deficient broilers than in the controls. The acid alpha-naphthyl acetate esterase-positive ratio of the peripheral blood T lymphocytes and the CD4 and CD8 numbers were markedly reduced (P<0.05 or P<0.01), and the CD4/CD8 ratio increased. Histopathologically, lymphocytes of lymphoid organs were depleted and the reticular cells of the thymus were also degenerate or necrotic in the Zn-deficient birds. The results demonstrate that Zn deficiency seriously inhibited the development of lymphoid organs, impaired the progression of lymphocytes from the G0/G1 phase to the S phase, and caused pathological injury in the lymphoid organs. The results also showed that the effect of Zn deficiency on the primary lymphoid organs occurred earlier than on the secondary lymphoid organs. The effect of Zn deficiency was greatest on the bursa of Fabricius, followed by the thymus, and then the spleen. Potential mechanisms underlying the observations are discussed.