Effect of a range of social stress severity on Escherichia coli challenge infection.

Chickens were exposed to various degrees of social stress 1 day before being exposed to Escherichia coli air-sac challenge exposure. Increasing levels of social stress resulted in increased heterophil/lymphocyte (H/L) ratios. Resistance to E coli air-sac challenge infection increased in correspondence with H/L ratios. However, as H/L ratios increased above the 0.72 value, there was a corresponding decrease in resistance to E coli challenge infection. Changes in H/L ratios, in response to social environment, differed with genetic stocks. Social stress was greatest when chickens housed singly for 3 weeks were placed among 5 unfamiliar chickens.