Abstract: In order to study the combined effects of yeast selenium and boron on development of immune organ and immune function of broilers, a total of 1 200 one-day-old AA broilers were randomly divided into five groups, the control group and the experimental groups Ⅰ, Ⅱ, Ⅲ and Ⅳ. Each group included 6 pens and 40 birds per pen. The control group was given a basic diet, while experimental groups Ⅰ, Ⅱ, Ⅲ and Ⅳ were given basic diets supplemented with 0.3 mg·kg^-1 yeast selenium and different doses of boron (0, 5, 10, 15 mg·kg^-1) for 42 days, respectively. The results showed as follows: 1) Compared with the control group at 21 days of age, the indexes of bursa of Fabricius and the areas of splenic node, periarterial lymphatic sheath and bursa nodule of Fabricius of broilers in experimental group Ⅱ and Ⅲ were significantly (P<0.05) increased; Serum Newcastle disease virus(NDV) antibody and interferon-γ (INF-γ) levels of broilers in experimental group Ⅱ and the serum interleukin-2 (IL-2) contents of broilers in experimental group Ⅲ were also significantly (P<0.05) increased. 2) Compared with the control group at 42 days of age, the indexes of thymus and bursa of Fabricius, and the levels of serum NDV antibody and IL-2, and the areas of splenic node, periarterial lymphatic sheath and bursa nodule of Fabricius of broilers in experimental group Ⅱ and Ⅲ were significantly (P<0.05) increased; the serum IgG and IFN-γ levels of broilers in experimental group Ⅱ were also significantly (P<0.05) increased; The indexes of thymus and bursa of Fabricius and serum IgG levels of broilers in experimental group Ⅰ were significantly (P<0.05) increased. Microscopic observation also showed that at 21 and 42 days of age, the microstructure of immune organs were improved in broilers of experimental group Ⅱ and Ⅲ, such as the structure of white pulp and red pulp of the spleen were clear, the boundary of thymus cortex and medulla was obvious, the node number of bursa of Fabricius were increased and the arrangement was compacted, and the size of bursa of Fabricius lobule also significantly (P<0.05) increased in experimental group Ⅰ. In conclusion, either the alone supplementation of yeast selenium or combined supplementation of yeast selenium and different doses of boron could promote the development of immune organs, improve microstructure and enhance the immune function of broiler to a certain extent, and combined supplementation of 0.3 mg·kg^-1 yeast selenium and 5-10 mg·kg^-1 boron had more obvious beneficial effects.

Key words: yeas selenium, boron, broiler, immune organ, tissue structure, immune function