1 │Introduction
Avian leukosis (AL), inducing malignant or benign tumorigenic diseases by avian leukosis virus (ALV), has caused immense economic losses all over the world in the poultry industry since its emergence(Payne & Nair, 2012; Weiss & Vogt, 2011). ALVs were divided into 11 different subgroups (designated A to K) based on cross neutralization and gp85 sequences(Dong et al., 2015). Among those, avian leukosis virus subgroup J (ALV-J) is the most prevalent subgroup in chickens and exhibits increasing pathogenicity and stronger vertical transmission ability in recent years (Li et al., 2016; Payne, Howes, Gillespie, & Smith, 1992; Venugopal, Howes, Flannery, & Payne, 2000). ALV-J infection used to be a common problem in poultry industry during 2003–2010, when its widespread causing the myelocytoma of broilers and haemangioma of layers(Cui, Du, Zhang, & Silva, 2003; Lai et al., 2011; Li et al., 2018; Li et al., 2013; Pan et al., 2012) . Because of the widespread distribution of the ALV-J strains, together with the less organized nature of the poultry industry especially among the local breeds of chickens, control and eradication of ALV in China remain a major challenge. Since 2018, a more tumorigenic ALV-J strain has appeared in the imported broiler breeders in China, inducing severe osteomas in keel and ribs, causing a massive pandemic, and hence becoming a major avian health concern. Therefore, many domestic farms have started self-checking for ALV infection.
Rubin and his colleagues defined four serological classes of susceptible birds: viraemia, no antibody (V+A−); no viraemia, with antibody (V−A+); viraemia, with antibody (V+A+); and no viraemia, no antibody (V−A−)(Payne & Nair, 2012; Rubin, Fanshier, Cornelius, & Hughes, 1962). Yet the researchers did not elaborate on the ALV infection status of male semen or the role of males in the transmission of ALV. During another study, Li found that roosters could spread ALV-J to hens by insemination and cause vertical transmission(Li et al., 2017). Therefore, roosters may be selected for freedom from Avian leukosis virus by ELISA tests of cloacal swabs or semen sampling, as well as virus isolation. However, the accuracy of these detection methods remains to be defined.
In this study, it was discovered ALV-J infection re-emerged in Hy-line brown roosters in recent years. Moreover, the hens were infectecd by insemination, and virus can be transmitted vertically to the breeding eggs. Several infection states of ALV-J in roosters were clarified and the reliability of different methods for detecting samples of males were compared. All those data may provide more detailed basis for the eradication of ALV.