Re-emergence of Avian leukosis virus subgroup J in the rooster of Hy-line brown layers and its transmission pattern in flocks

Abstract Avian leukosis virus subgroup J (ALV-J) is the most prevalent subgroup in chickens and exhibits increasing pathogenicity and stronger horizontal and vertical transmission ability among different kinds of chickens. Although vertical transmission of ALV-J from hens infected through artificial insemination was reported before by the detection of swabs and serum, but there was no further research on the transmission pattern of ALVs in the roosters. In the present study, the introduction of Hy-line brown roosters significantly increased the p27 positive rate of ALV in an indigenous flock detected by ELISA and virus isolation. Sequence analysis and IFA showed that it is classified into ALV-J subgroup, locating in a new branch compared with the domestic and foreign referential sequences. Meanwhile, the gp85 gene of the ALV-J isolated in the hens and its albumens had a homology of 94.1–99.7% with that in the roosters, which means that the strain is quite likely transmitted to the hens and their offspring through insemination of the roosters. In addition, there are four ALV-J infection status in plasma and semen of rooster (V + S+, V-S+, V + S-, V-S-), so the eradication of ALV in rooster requires simultaneous virus isolation of semen and plasma. Additionally, compared with ALV detection in samples by DF-1 cells, directly detecting ALV in semen by ELISA exists some false positives. Collectively, our results suggested that the incomplete eradication process of roosters leads to the sporadic findings of ALV-J in laying hens