In order to determine the causative agents responsible for the lethality of tumor disease in breeders,liver,spleen and other tissues of dead chickens were collected,and pathogen detection,se-quencing and genetic evolution analysis were carried out by PCR.The results showed that all three samples were negative for reticuloendotheliosis virus(REV),samples 1 and 2 wereavian leukosis virus subgroup J(ALV-J)positive,and sample 3 was positive for ALV-J and Marek's disease virus(MDV),which preliminarily determined that the breeder died of ALV-J infection or ALV-J and MDV mixed infection.Among them,the ALV-J gp85 gene had the highest nucleotide homology with the reference strain of ALV-J,ranging from 87.70％to 99.30％,and was in the same branch with the reference strain of subgroup J.Amino acid homology ranged from 78.00％to 96.20％,with some mutations.The nucleotide homology between the MDV meq gene and the vv+strain was the highest,which was 98.00％-99.00％,and they were in the same branch.The homology of amino acids was 95.90％-98.20％,and there were multiple mutation sites,among which the 176th amino acid destroyed the original Pro repeat of the virus MDV meq due to the mutation of Pro to Arg or Ala,which may lead to the enhancement of its virulence.This study will provide a reference for the prevention and control of neoplastic diseases in breeders in this region.

In order to determine the causative agents responsible for the lethality of tumor disease in breeders,liver,spleen and other tissues of dead chickens were collected,and pathogen detection,se-quencing and genetic evolution analysis were carried out by PCR.The results showed that all three samples were negative for reticuloendotheliosis virus(REV),samples 1 and 2 wereavian leukosis virus subgroup J(ALV-J)positive,and sample 3 was positive for ALV-J and Marek's disease virus(MDV),which preliminarily determined that the breeder died of ALV-J infection or ALV-J and MDV mixed infection.Among them,the ALV-J gp85 gene had the highest nucleotide homology with the reference strain of ALV-J,ranging from 87.70％to 99.30％,and was in the same branch with the reference strain of subgroup J.Amino acid homology ranged from 78.00％to 96.20％,with some mutations.The nucleotide homology between the MDV meq gene and the vv+strain was the highest,which was 98.00％-99.00％,and they were in the same branch.The homology of amino acids was 95.90％-98.20％,and there were multiple mutation sites,among which the 176th amino acid destroyed the original Pro repeat of the virus MDV meq due to the mutation of Pro to Arg or Ala,which may lead to the enhancement of its virulence.This study will provide a reference for the prevention and control of neoplastic diseases in breeders in this region.