الفهرس 
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Abstract
Seventy nine chicken flocks were investigated for the presence of NDV using RT-PCR F-protein gene assay using degenerate primers specific for velogenic strains of NDV, 23 flocks tested positive for vNDV. Four representative isolates were sent for partial sequencing of the F-Protein gene. Results revealed that all isolates have multiple basic A.A at the F-Protein cleavage site possessing the velogenic motif (112.RRQKR*F.117). Phylogenetic analysis of the F-protein 375 b.p. hyper variable region (nt 47– 422), revealed that all isolates are belonging to genotype VIId with (98%-99%) amino acid identity matrix with the Israelian2 (Turkey-Israel-111-2011) and Chinese2 (Chicken-China-SDYT03-2011) strain, Genotype VIId. Single pure NDV isolated strain was selected (NDV/chicken/EG-QU/NRC/2015, acc .No. MF418018) after testing negative for AI (H5, H9), IB virus. Titration of the selected strain reveals MDT of (36 hr.) and 107.7 EID50/ 0.1 ml. In vivo vaccination protection study was done using different vaccination programs for protection against challenge with the locally isolated (NDV/chicken/EG-QU/NRC/2015, acc.No. MF418018).Commercial broiler chicks were divided in to 7 different vaccination groups including positive non-vaccinated control group. Results revealed that group vaccinated with La Sota with inactivated NDV vaccine showed 100% protection rate against mortality and emergency vaccination after challenge using La Sota vaccine gave the best result. Cloacal viral shedding was decreased in vaccinated groups with La Sota and Avinew but not completely prevented. group no.1 and 4 were showing a high mean HI titer than other groups and least viral shedding following infection, while group’s no. 3 and 6 are showing a lower mean HI titer and protection rate than other groups. Possible causes of these results were discussed in details.