الفهرس 
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Abstract
The immunomodulating effects of three antibacterial agents namely Amoxicillin, F.
Nizone (nidroxyzone + propionic acid) and Florfenicol and one probiotic (BioPlus- 2B) on
broiler chickens were studied. The growth performance parameters were reported. The daily
therapeutic doses of the antibacterial agents were used for five successive days in drinking
water and the probiotic was added to feed of designated group all time of the experiment.
Amoxicillin treatment decreased the cellular (chicken interferon gamma ChIFN),) and
humoral (Haemagglutination inhibition HI) immune response to Newcastle disease virus
(NDV) challenge but the protection was 5/5. A significant transient decrease of the
Iymphocyte and heterophil count, and a significant decrease of (:3- and -y-globulins were noted
due to amoxicillin treatment. The growth performance improved significantly by amoxicillin.
Both F. Nizone and florfenicol caused a significant depression of the cellular and humoral
immune response to NDV challenge inspite of complete protection (5/5). The number of
lymphocyte and heterophil decreased significantly by both drugs. F. Nizone caused
a significant decrease of (:3- and ),-globulins, moreover it depressed the growth performance of
the chicken. Florfenicol treatment depressed the )’-globulin level and improved the
performance non significantly. The used probiotic increased ChIFN), in response to NDV
challenge and decreased HI titer 24 and 48 hours post challenge and the protection was 4/5.
Probiotic caused a significant improvement in the broiler growth peformance and had no
effect on leukogram and serum proteins.
The obtained results showed that the use of probiotic lead to shift of the chicken immune
response toward Th1 in response to NDV challenge. Regarding the collective results it could
be concluded that the issue is not the level but the pattern and speed of the immune response
and the coordination of different players of the immune system in response to acute infection.