Effect of Social Stress on Occurrence of Marek's Disease in Chickens

SUMMARY Among chickens exposed to a high degree of social stress (hss) or selected on the basis of a high concentration of plasma corticosterone (hpc), there was an increased incidence of Marek's disease. Chickens exposed to a low degree of social stress (lss), or selected on the basis of a low concentration of plasma corticosterone (lpc), or were fed dichlorodiphenyldichloroethane (ddd) had Marek's disease less frequently. Concentrations of ddd which were larger or smaller than the optimal dose (250 p.p.m.) were less effective. The effectiveness of ddd in reducing the frequency of tumors continued for at least 5½ weeks after treatment.