Effect of social stress on Newcastle disease virus (LaSota) infection.

Individual immature chickens were socially stressed when placed into an established group of chickens. The stress response was determined by periodic measurement of plasma cortisol and by determination of the relative regression of the bursa of Fabricius. Stressed chickens had elevated cortisol levels during the first 24 hours following the initiation of social stress. The bursa-to-body-weight ratios of stressed birds at 96 hours following stress were significantly lower than the ratios in control birds, and their tuberculin reaction was significantly depressed. Newcastle disease virus was more invasive and attained higher titers in stressed birds. The hemagglutination-inhibition (HI) response of the stressed birds was higher in one trial and lower in another.