الفهرس 
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Abstract
Thyroid hormones have clear effect on broilers growth either normal or experimentally infected with runting stunting syndrome. Our study aimed firstly to make preliminary study on 20 chicks to choose the best method for the main experiment. Oral infection of one day old chicks was done, GP- 1 was control negative and takes normal saline, GP- 2 infected with reovirus field strain by a dose 2 ml containing 104.5 TCID50, GP- 3 infected with intestinal homogenate 0.2 ml that obtained from normally infected chickens with runting stunting syndrome (confirmed by ELISA), GP- 4 infected with a mixture the previous of reovirus field strain by a dose 1 ml containing 104.5 TCID50+ intestinal homogenate 0.1 ml. We choose the forth group method of infection. Secondly, the main experiment was made on 165 one day old chicks which were divided to 11 groups, 5 groups only at one day old were experimentally infected with the chosen source of infection till the 3rd week old age then thyroid hormones treatment were conducted (0.1, 0.5, 1 ppm triiodothyronine) and (1, 3 ppm thyroxin). The other five groups which were non-infected had the same hormonal treatments. The eleven group was control negative. Growth indices, hematological picture and biochemical profiles at 4, 6, 8 weeks old age were determined. Results cleared that growth performances were better in non- infected hormonal treated groups in comparison with both control and infected hormonal treated groups by the same doses. Moreover, the low thyroid hormones doses gave better results in comparison with higher doses. Histopathology showed some pathological changes in infected high hormonal treated groups; on the other hand, better histopathological pictures were seen in both infected and non-infected low doses hormonal treated ones. Serum and plasma samples of low doses non-infected hormonal (triiodothyronine and thyroxin) treated groups revealed better results in comparison with both control and higher doses hormonal treated groups also non-infected in comparison with infected with the same doses.