Late in 2016, multiple reassortant highly pathogenic (HP) avian influenza virus (AIVs) H5N8 was detected. AIVs infect different isolated hosts with a specific viral tropism. In the current study, the whole genome of the Egyptian A/chicken/NZ/2022 was genetically characterized. The H5N8-A/Common-coot/Egypt/CA285/2016, A/duck/Egypt/SS19/2017 previously isolated in Egypt, and the recently circulating A/chicken/Egypt/NZ/2022 reassortant viruses' replication, pathogenicity, and viral load in comparison to the H5N1-Clade 2.2.1.2 were investigated on Madin-Darby canine kidney cell (MDCK), by using the cytopathic effect (CPE) percent and matrix-gene reverse transcription quantitative real-time polymerase chain reaction to compute the virus titer at various points in time. The A/chicken/Egypt/NZ/2022 virus was similar to the reassortant strain clade 2.3.4.4b discovered in farms in 2016. The 2 sub-groupings of hemagglutinin (HA) and neuraminidase (NA) genes were identified (I and II); the A/chicken/Egypt/NZ/2022 HA and NA genes were associated with subgroup II. The subgroup II of the HA gene was further divided into A and B owing to acquired specific mutations. The A/chicken/Egypt/NZ/2022 in our study was associated with subgroup B. The M, NS, PB1, and PB2 genes were shown to be clustered into clade 2.3.4.4b by full genome sequence analysis; however, the PA and NP genes were found to be associated with H6N2 viruses, which had particular mutations that improved viral virulence and mammalian transmission. The current results showed that the circulating H5N8 viruses were more variable than previous viruses analyzed in 2016 and 2017. Compared to other reassortant HPAI H5N8, and HPAI H5N1, the growth kinetics of A/chicken/Egypt/NZ/2022 had a high CPE without the addition of trypsin and the most viral copies with a significant difference (P < 0.01) in comparison to HPAI H5N8 and HPAI H5N1 reassortant viruses. Accordingly, the effective viral replication of A/chicken/Egypt/NZ/2022 in the MDCK than other viruses may play a factor in the spread and maintenance of specific reassortant H5N8 influenza virus in the field.