Avian leukosis virus subtype J (ALV-J) remains a persistent threat to the poultry industry. To address a decade-long data gap in Taiwan, we surveyed 41 colored-broiler or layer farms using field-submitted, tumor-suspect samples collected between 2021 and 2023. Eight ALV-J–positive cases were detected, including five clade 2 and three clade 1, no clade 3 cases were found. Three of the eight cases showed co-infection with ALV-K. Sequence analysis of gp85 from newly isolated ALV-J viruses, together with historical Taiwan isolates from 2000 to 2010, revealed a shift from HPRS-103-like (clade 1) to ADOL-7501-like (clade 2) viruses. Although multiple 3′UTR conformations were observed, the DR-1 element remained conserved. To assess the infectivity of current Taiwanese strains, we used the RCAS system to generate recombinant viruses harboring the clade 2 env and the DR-1 region, showing an enhancement of replication kinetics in DF-1 cells compared to env alone. Our results indicate that DR-1 promotes clade 2 replication, consistent with prior findings on clade 1. These data confirm the continued circulation of ALV-J in Taiwan, ongoing genomic evolution, and field co-infections of ALV-J and ALV-K. Our findings provide updated baseline information that can inform future monitoring and control strategies across Taiwan’s diverse poultry production systems.

To Cite This Article: Wu CH, Shin DL, Cheng YW, Huang WH and Wu NH, 2025. Clade dynamics and persistence of alv-j in taiwan poultry populations. Pak Vet J. http://dx.doi.org/10.29261/pakvetj/2025.342