الفهرس 
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Abstract
The present study aimed to : identify the most important respiratory viruses that may infect broiler chicken flocks under Egyptian environmental conditions A total no.44 flocks at Alexandria, El-B¬ehera, Kafr El-Sheikh governorates which suffered from high mortality rates with Respiratory manifestation and diarrhea. History of investigated flocks (location, Age, Total numbers, mortality of last 3 days and Vaccination program) were recorded. Samples including Trachea and Lungs were collected, processed and inoculated into fertile SPF eggs at 10 days old via AS route.
The embryo mortality pattern and lesions were recorded and The Allantoic fluid was collected for HA test and PCR technique for detection of AIV (H5, H9), NDV and IBV.
* This study indicated the following :
These flocks were suffering from high mortality with sever respiratory symptoms such as coughing, sneezing and swollen sinuses with swollen eyes, also some flocks were suffering from breathing difficulty (gasping) with Different diarrhea in the back of the chicken.
Some flocks have also suffered from neurological symptoms and paralysis with heamorrage on the legs with a low consumption of feed and water, these birds were 14 and 49 day old and itheir number ranged between 1000 and 20000 and the mortality rates ranged between (0.56%) and (3.9%) .
The post-mortem examination results showed the flocks in general congestion in the body parts with congestion in trachea and pneumonia in some flocks while other flocks showed plug at the end of the trachea (Caseated plug) and other having heamorrage in proventriculus and the deodenum with swelling and inflammation of the spleen and the kidneys.
The results of viral isolation and molecular identification indicated :
A. Percentage of flocks of Newcastle virus infection as follows in El-Behera at a rate of : number (8) flocks by (53.34%), number (6) flocks in Alexandria by (42.85%) and number (6) flocks in Kafr El-Sheikh by (40%).
B. Percentage of avian influenza virus infected flocks ( H5) highly pathogenic in the governorate of Alexandria at a rate of: number one flocks by (6.67%) and no infection recorded with this virus in El-Behera and (2) flocks in Kafr El-Sheikh.