الفهرس 
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Abstract
The present study was conducted to evaluate the effect of different zinc sources and doses on production performance, immune response and histopathological effect on some internal organs of broiler chicks. 300 (one day old) broiler chicks were divided into 6 groups. group one(not vaccinated), fed basal diet containing 80 mg/kg ZnO(zinc oxide); group two, as a control (vaccinated) fed basal diet containing 80 mg/kg ZnO(zinc oxide); group three, fed diet containing 120mg/kg ZnO(zinc oxide) added to basal diet; group four, fed diet containing 320mg/kg ZnO(zinc oxide) added to basal diet; group five, fed diet containing 120mg/kg ZnMeth (zinc methionine) added to basal diet; and group six, fed diet containing 320mg/kg ZnMeth (zinc methionine) added to basal diet. Antibodies responses were monitored based on hemagglutination inhibition and ELISA assay for detection of IgG. Average body weight gain and feed conversion ratio were estimated to evaluate zinc growth promoting effect. Histological sections were obtained to study the effect of zinc on some internal organs. Antibodies titers of group four(400mg zinc oxide), five(200mg zinc methionine) and six(400mg zinc methionine) at 35 days of age using hemagglutination inhibition test show significant difference than group two (control), but there is no significant difference between these groups (group four, group five and group six). ELISA assay confirmed the significance between control group and groups of supplemental Zinc at day 21 and 35 , the antibody titers against BSA(bovine serum albumin) inoculation varied significantly (P 0.05) with the level of supplemental Zinc. Highest antibody titers were observed at group six (400mg zinc methionine).
The antibody titers of organic zinc source (zinc methionine) at group five (200mg zinc methionine) and six (400mg zinc methionine) were higher than groups of non-organic zinc (zinc oxide) of group three and four at the same doses. Non-significant interaction between Zinc sources and Zinc levels on performance and the FCR (feed conversion ratio) was not improved at dietary levels of Zinc exceeding the NRC (national research council) recommendations of 40 mg/kg diet. The histopathological results show no significant histopathological lesions were found in the bursa of fabricius, spleen, thyroid gland, cecal tonsil. Except for liver at higher doses of zinc oxide and zinc methionine that showed congestion and inflammatory cell infiltration, respectively. The results of histological study can be implicated by being apparently healthy of the birds throughout the duration of the study and this indicates that the used doses and sources were safe on these organs and did not cause damage to their histological structure.
from the previous results, the following can be deduced:
-Supplementation of feed with zinc causes activation of the humoral immune response in poultry.
-Organic zinc (zinc methionine) improves immune response more than inorganic zinc (zinc oxide) at the same dose.
-supplementations of zinc at dose higher than NRC not improve production performance.
-The histological study shows that the used doses and sources were safe on internal organs and did not cause damage to their histological structure.