Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 10, 1997
Publication Date: N/A
Interpretive Summary: Because of ease of use and economic advantage, sex identification of chickens carrying the late-feathering (LF) trait has long been used by commercial chicken breeders. However, this trait has been shown to be associated with an endogenous virus-21 (EV21) which renders chickens highly susceptible to avian leukosis, a virus-induced cancer-like disease. The effect of contact and genetic transmission of EV21 on response of chickens exposed to avian leukosis virus (ALV) at various ages is not known. Results from our study suggest that: a) contact exposure of chickens to EV21 has no influence on development of avian leukosis and b) exposure of LF chickens harboring EV21 to ALV at 4 weeks or older will not increase susceptibility of chickens to the disease. The data also indicate that the enhancing effects of EV21 on avian leukosis could be avoided if early exposure to ALV is delayed. Because in commercial crosses LF female breeders can congenitally infect their progeny with EV21, it is important that efforts should be made to avoid early exposure of progeny to ALV. This research will assist chicken breeders in their effort to control avian leukosis in chicken lines carrying LF trait.
Technical Abstract: The role of contact and genetic transmission of endogenous virus (EV21) on response of chickens to avian leukosis virus (ALV) infection and tumors was studied. F1 progeny of a cross between RPRL late-feathering (LF) line, EV21+ males and RPRL early feathering (EF) line 15B1 females harboring or lacking EV21 were used. EF chicks lacking EV21 were contact-exposed to LF EV21+ hatchmates for various time intervals following inoculation with a field strain of subgroup A ALV at hatch. In a second experiment, EV21 contact-exposed and unexposed EF chicks as well as LF EV21+ hatchmates were inoculated with ALV at various ages. Chickens were tested for ALV-induced viremia and antibody and observed for tumors for 24 weeks of age. Antibody to EV21 in EF chickens were contact-exposed to LF EV21+ hatchmates varied from 10% to 44% and was not detected before 10 weeks of age. By 24 weeks of age, ALV-induced viremia and tumors in EF chickens varied from 5%-13% and 15%-32%, respectively, regardless of exposure to EV21. The incidence of ALV-induced tumors was significantly higher in LF chickens genetically-infected with EV21 than that in EV21 contact-exposed or unexposed EF chickens; but only in chickens inoculated with ALV at hatch. The data suggest that contact infection with EV21 has no influence on ALV infection and tumors. The data also suggests that genetic transmission of EV21 may increase susceptibility of chickens to ALV infection and tumors following infection with ALV at hatch; but not at 4 weeks of age or older.