Studies of avian leukosis virus infection in chickens from a commercial breeder flock.

Progeny chicks from a commercial breeder flock with a high rate of avian leukosis virus (ALV) infection were classified as congenitally or contact infected with ALV on the basis of virus tests on their meconia at hatching and the presence or absence of antibodies at 20 weeks of age. The ALV infection profile, shedding, tumor mortality, and egg production in the congenitally-infected chickens were compared with those in the contact-infected hatchmates. Results show that viremic-tolerant hens classed as congenitally infected consistently shed virus into albumen of their eggs and progeny and 18% died from tumors. In contrast, hens classified as contact infected had a transient viremia; most of them developed antibody to ALV, and only 10% shed virus into albumen and progeny. No mortality from tumors occurred in this group of chickens during the 48-week experimental period, and egg production was significantly higher than in the group classified as congenitally infected. In addition, progeny chickens hatched from the contact-infected group maintained a low rate (2.9 to 3.8%) of ALV infection for the next two generations without further selection. These data further document principles and procedures for reduction of ALV infection in commercial flocks and the considerable economic benefits to be derived therefrom.