Studies of flocks with high mortality from lymphoid leukosis.

Two pairs of commercial white-egg parent flocks were selected for study, because one of each pair was observed to be dying with lymphoid leukosis at a high rate. The proportion of each flock producing eggs with lymphoid leukosis virus in the albumen was studied. In one pair the rate of birds shedding was no different in the high- and low-mortality flocks. The total rate of shedding was lower in the other pair, but the rate was higher in the high-mortality flock. These data indicate that the rate of virus infection is not always proportional to the development of lymphoid leukosis, and that other environmental factors may play a role. Direct complement-fixation tests on the albumens which were positive for lymphoid leukosis virus showed that group-specific antigen could be detected in 83%. Therefore, the direct complement-fixation test can be used on albumens as a rough estimate of shedding rate.