CONTROL OF LYMPHOID LEUKOSIS IN A FLOCK WHITE PLYMOUTH ROCK CHICKENS

Lymphoid leukosis (LL) was successfully controlled in a commercial basic breeding line of White Plymouth Rock chickens. The control method was developed for breeder flocks and consisted of 3 elements. In the flock under study, homogenates of embryos from all eggs collected for 14 days are tested for the presence of LL viruses. Only eggs from hens that do not shed virus in their eggs are used for the production of progeny. The offspring are reared in isolation during the first 2 mo. of life, at which time the age related resistance against tumor formation by LL viruses appears sufficiently developed. The chickens are subsequently inoculated i.m. with LL viruses of subgroups A and B and transferred to a conventional chicken house. The vaccination raises a solid immunity to horizontal LL virus exposure and, due to the age-related resistance, tumor formation does not follow. No excretion of LL viruses could be detected in 3 generations of White Plymouth Rock chickens to which the 3 elements of the control procedure were applied. Clinical disease was not observed in any of the chickens under notice.