Submitted to: Avian Pathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/9/2003
Publication Date: 5/1/2004
Citation: Bacon, L.D., Fulton, J.E., Kulkarni, G.B. 2004. Methods for evaluating and developing commercial chicken strains free of endogenous subgroup E avian leukosis virus. Avian Pathology. v. 33(2). p. 233-243. Interpretive Summary: Avian leukosis viruses (ALV) are economically important. Exogenous ALV of several types spread through the environment and can cause cancer-like diseases and other production problems. Endogenous ALV (ALVE) are inherited through the genes and may decrease productivity but are not associated with disease. Most chickens are susceptible to ALV and contain ALVE. However, a special line termed line 0 has been developed lacking ALVE, and has total resistance to ALVE, while being susceptible to exogenous ALV. Line 0 has been invaluable for differentiating exogenous from endogenous ALV. We describe the development of a new line 0-type chicken by crossing line 0 with a productive commercial chicken line and then conducting current selection methods to yield breeders that lack ALVE and have resistance to ALVE but susceptibility to exogenous ALV. This information will be useful to scientists in academia and vaccine manufacturing.
Technical Abstract: The genome of nearly all chickens contains various DNA proviral insertions of retroviruses of subgroup E avian leukosis virus (ALVE). However, the elimination or control of ALVE gene expression is desirable to improve productivity, have resistance to avian leukosis virus (ALV) induced tumors, and to develop safer live virus vaccines in chick embryos. RFLP and PCR methods are used to define the presence of ALVE genes; and the expression of ALVE in chicken plasma or on cells, and the susceptibility of cells to ALVE, is determined by flow cytometry using a specific (R2) antibody. ADOL line 0 chickens have been selected to be free of ALVE genes, while being resistant, i.e. lack receptors, to ALVE, but susceptible to exogenous ALV, i.e. ALVA, ALVB, ALVC and ALVJ. To develop improved line 0-type chickens, ADOL line 0 was outcrossed to a commercial line that had one ALVE gene, and evidence for ALVE resistance. Rous sarcoma virus (RSV) challenge was used to confirm resistance of F1 chickens to ALVE, and susceptibility of F2 breeders to ALVA and ALVB using test chicks produced by matings to line 72. Selected F2 breeders were resistant to ALVE, but susceptible to exogenous ALVA, ALVB, ALVC and ALVJ, based on challenge tests of progeny chick cells using an ELISA. The new line, 01, had improved egg size, productivity, fertility and hatchability. Similar procedures may be used for development of productive ALVE free chicken lines with preferred ALV susceptibility traits.