Eradication of subgroups A and B lymphoid leukosis virus from commercial poultry breeding flocks.

A specific-pathogen-free pedigreed breeding population of White Leghorns was determined to be free of lymphoid leukosis subgroups (LL-A and LL-B) on the basis of the standard resistance-inducing factor (RIF) test of sera of individual birds. The fourth pedigreed generation (G-4) was the first to test free of viruses of both sub-groups. In three subsequent pedigreed generations (G-5 through G-7) no viremic birds were found. The RIF test of sera was also used to detect carriers infected with LL-A and LL-B in sample populations of commercial broiler, brown-egg layer, and other White Leghorn breeding lines. When only known nonviremic dams were used for reproduction, in only one instance were viremic birds detected in samples of their progeny in succeeding generations. Some implications for a virus-free breeding program are discussed.