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Precipitating antibody development in birds infected with Marek's disease virus.

SUMMARY Active precipitating antibody appears as early as 2 weeks after 10-week-old birds are exposed to Marek's disease. Older birds develop antibodies earlier and in higher titers than younger birds. Exposure at an older age gives a more uniform antibody response and less mortality. The level of antibody appears to be related to protection but is not constant, and birds can go from positive to negative. It also appears that the antibody response of the bird is a critical factor in survival.