effect of different levels of zinc on the performance and humoral immunity response in broiler chicken

this experiment was conducted to evaluate the effects of different levels of zinc on the performance and humoral immunity response in broiler chickens with 250 ross broiler chickens with five experimental treatments consisted of five replicates in a completely randomized design. treatments were diets containing: basal diet (control) and basal diet plus 40, 80, 120 and 160 mg zn/kg. results of the experiment indicated that birds were fed on diets containing 120 mg zn/kg and control showed the highest and the lowest weight gain, respectively (p 0.05). in connection with feed conversion ratio, the highest and the lowest means belonged to the treatments containing 40 and 120 mg zn/kg respectively (p 0.05). regarding bronchitis antibody titer in 13th and 19th days, the lowest titer belonged to the birds on the control and 40 mg zn/kg and the highest titer belonged to the birds fed with 160 mg zn/kg. the difference between this treatment and the others was significant (p 0.05). in secondary srbc at 36 days of age the best and the lowest titer were shown by 40 mg zn/kg and 160 mg zn/kg of diet, respectively(p 0.05). finally, the results indicated that addition of 120 mg zn/kg, of diet improved weight gain and feed conversion ration. the levels of 40 and 160 mg zn/kg of diet showed the highest immunity response against srbc and bronchitis respectively.