Submitted to: Avian Pathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/8/2007
Publication Date: 7/10/2007
Citation: Zhang, H.M., Bacon, L.D., Heidari, M., Muir, W.M., Groenen, M.A.M., Zhang, Y., Wong, G.K.S., Fulton, J.E., O'Sullivan, N.P., Albers, G.A.A., Vereijken, A.L.J., Rattink, A.P., Okimoto, R., McKay, J.C., McLeod, S., Cheng, H.H. 2007. Genetic variation at the tumour virus B locus in commercial and laboratory chicken populations assessed by a medium-throughput or a high-throughput assay. Avian Pathology. p. 283-291. Interpretive Summary: One virus potentially threatening the poultry industry is avian leukosis virus which contains six subgroups. Major breeding companies have been doing a superior job in eradicating five subgroups of this virus. However, a problem persisting is that many chickens continue to carry one subgroup, and a method for improving genetic resistance is important. This research defines two new methods to distinguish genetic resistance to three subgroups of avian leukosis virus, and identifies ways to reduce genetic susceptibility to these viruses through selection. Reduction in susceptibility to these viruses will improve chicken health and productivity, and reduce the potential for development of new recombinant avian leukosis viruses.
Technical Abstract: The tumor virus B (TVB) locus transcribes three major alleles, TVB*S1, TVB*S3, and TVB*R. TVB*S1 encodes a cellular receptor mediating infection by three subgroups of avian leukosis virus (B, D, and E). TVB*S3 encodes a receptor for two subgroups (B and D), and TVB*R encodes a dysfunctional receptor that does not permit infection by any of the subgroups, B, D, or E. For the first time genetic diversity at the tumor virus susceptibility locus B was investigated in diverse chicken populations using 3,035 chickens from 36 commercial and 14 experimental lines. Genotyping was accomplished with a medium and a high throughput assay. In commercial broilers, more than 1/3 of the lines are fixed for the most susceptible TVB*S1 allele. On average 83% chickens were typed as TVB*S1/*S1, 3% as TVB*R/*R, and 14% as TVB*S1/*R. Similarly, about 1/3 of the commercial egg-layer lines was fixed for TVB*S1/*S1. About 44% egg-layers were typed as TVB*S1/*S1, 15% as TVB*R/*R, and the rest as heterozygotes (TVB*S1/*S3, TVB*S1/*R, and TVB*S3/*R). In the experimental chickens 60% were fixed for TVB*S1/*S1, 6% for TVB*S3/*S3, 14% for TVB*R/*R, and the rest were heterozygotes (TVB*S1/*S3 and TVB*S1/*R). Overall 90% of the chickens are genetically susceptible to one or all of the B, D, and E subgroups of avian leukosis virus. The current study uncovers the severity of genetic risk that the US chicken populations are facing. However, the study also shows that 30% of chickens in the current populations carry one or two TVB*R alleles, which suggests genetic improvement for resistance to subgroup B, D, and E avian leukosis virus is possible.