The purpose of this 42-day study was to investigate the effects of methionine (Met) deficiency on immune function by determining the relative weight, morphological and ultrastructural changes of bursae of Fabricius, cell cycle, and apoptosis of bursa cells. One hundred and twenty one-day-old avian broilers were randomly divided into two groups and fed on a control diet (starter diet, Met 0.50%; grower diet, Met 0.40%) and Met-deficient diet (starter diet, Met 0.26%; grower diet, Met 0.28%) for six weeks. The relative weight of bursae was decreased with Met deficiency when compared to that of the control group. Lesions were also observed in the
Met-deficient group. Histopathologically, the numbers of lymphocytes in the follicles were decreased. Ultrastructurally, the mitochondria of lymphocytes were swollen in the
Met-deficient group. As measured by flow cytometry, bursal cells in the G0
phase were significantly higher (P
< 0.01), and bursal cells in the S, G2
M phases and proliferating index were obviously lower (P
< 0.01) with Met deficiency than in the control group. Moreover, the percentage of apoptotic cells in the bursae were significantly increased in Met-deficient birds (P
< 0.01). It was concluded that Met deficiency restrained the development of the bursae of Fabricius and affected the humoral immunity of the chickens.