Studies of Flocks with High Mortality from Lymphoid Leukosis

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Abstract
Two pairs of commercial white-egg parent flocks were selected for study, because 1 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 albumin was studied. In 1 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 other environmental factors may play a role. Direct complement fixation tests on the albumins which were positive for lymphoid leukosis virus showed that group-specific antigen could be detected in 83%. The direct complement fixation test can be used on albumins as a rough estimate of shedding rate.