Endogenous Viral Genes: Association with Reduced Egg Production Rate and Egg Size in White Leghorns

Abstract

Endogenous viral (ev) genes are DNA sequences residing permanently in the genome of most chickens that have a high degree of homology to avian leukosis viruses (ALV). Association of ev genes with production trait differences was studied in White Leghorns free of exogenous ALV. The Cornell Strain K and S chickens used in Experiment 1 had multiple ev genes. In each of four lines of chickens in Experiment 2, there was a 1:1 segregation of full-sibs free of ev genes and those carrying one ev gene: ev-12 that produces the complete endogenous virus, ev-3 or ev-6 that express certain viral antigens, or ev-1, a silent gene. In Experiment 1, the presence of genes ev-10 or ev-19, known to produce the complete virus, was associated with a 9% reduction in the annual egg production rate (P less than .05) in Strain S. Similarly, the presence of the virus-producing ev-12 in Experiment 2 was associated with an 8% reduction of annual egg production rate (P less than .05), a 2.2-g reduction in egg weight (P less than .01), and a .003 reduction in egg specific gravity (P less than .01). No significant effects of ev genes on age at first egg, Haugh unit score, percentage of eggs with blood spots, and body weight of hens were observed. It was concluded that ev genes producing complete endogenous virus are associated with production trait differences similar to those associated with subclinical infections with exogenous ALV.

Genetic variation at the tumour virus B locus in commercial and laboratory chicken populations assessed by a medium-throughput or a high-throughput assay

“…ALV-J causes myeloid tumours primarily in broilers (Chai & Bates, 2006). In addition to inducing tumours, ALV also reduces productivity, causes immunodepression, and other production, reproduction and health problems in affected flocks Gavora et al, 1991;Bacon et al, 2000;Fadly & Payne, 2003).…”

“…ALV-D and ALV-C are rarely isolated from the field. ALV-E is rarely oncogenic but is commonly isolated from both egg-layer type and broiler chickens Ignjatovic, 1988;Gavora et al, 1991). ALV-E alone constitutes the endogenous virus group and transmits vertically from hen to chick (Fadly & Payne, 2003).…”

Endogenous viral genes influence infection with avian leukosis virus

“…These observations together with earlier findings that the birds possessing such genes have reduced egg production performance (Gavora et al, 1991) indicate that these genes should be eliminated from layer breeding stocks. SMITH, E.J., FADLY, A.M. & CRITTENDEN, L.B.…”

“…Semicongenic lines EV01, EV03, EV06, EV12, developed at the Avian Diseases and Oncology Laboratory, USDA, East Lansing, MI, each segregated for the ev gene corresponding to the line number, but were free of other ev genes (Gavora et al, 1991). Chickens for this study were produced in Ottawa within each of the lines by mating males that were heterozygous (hemizygous) for one ev gene to females without any such genes.…”

Comparative analysis of avian leukosis virus-related endogenous viral genes in experimental strains of the domestic chicken

“…However, ev6 was found to be associated with higher susceptibility to Marek's disease (Kuhnlein et al, 1989b) and lower immunoresponsiveness (Lamont et al, 1992). (Gavora et al, 1991) or to linkage with production trait genes for silent ev genes (Kuhnlein et al, 1989b). Thus, endogenous viral genes can be proposed for mapping studies (Crittenden, 1991).…”