Studies on the associations between natural infection of hens, cocks and their progeny with lymphoid leukosis virus.

Associations have been studied between natural infection of hens and cocks in a commercial flock with subgroup A lymphoid leukosis virus (LLV) and the presence of LLV in their eggs and progeny. Whole blood and sera were examined for LLV and virus-neutralising antibody, and vaginal swabs and semen samples were examined for LLV. Egg albumen samples were tested for LLV and group-specific (gs) antigen and embryos for LLV. Of 198 hens, 63.6% were immune, non-viraemic, 7.1% tolerant viraemic, 2.5% immune, viraemic and 26.8% non-immune, non-viraemic. Genetic resistance may have accounted for the last of these classes. A low rate of infection was found in the 40 cocks studied and the possible reason for this is discussed. There was no evidence that they were responsible for congenital transmission of LLV. Strong associations were observed between LLV in vaginal swabs or serum of hens and LLV or gs-antigen in albumen in their eggs. Significant but weaker associations were observed between these traits in the hens and LLV in their embryos, and between LLV and gs-antigen in egg albumen and LLV in embryos. Testing of whole blood for LLV showed little advantage over testing of serum. The efficiency of various tests for detecting hens least likely to transmit LLV to their progeny was examined. The lowest rates of embryonic transmission, which were 7-fold lower than the overall transmission rate, occurred in hens of two classes: those negative for viraemia, LLV in vaginal swabs, and antibodies, and those negative for LLV in vaginal swabs, antibodies and LLV or group-specific antigen in their egg albumen. The implications of these findings are discussed.