Summary
Chickens in a low-stress environment (heterophil/lymohocyte ratio 0.31) were given feed containing 30, 40, or 60 mg of corticosterone/kg of feed for 0.5 hour. Between 0.5 to 12 hours later, chickens were exposed to Escherichia coli via the air sac route. For each dose of corticosterone, there was an untreated control group that was exposed to E coli via the air sac route. The prevalence of pericarditis was reduced from 78 to 7% between 2 and 4 hours after exposure. Resistance was associated with heterophil/lymphocyte (h/l) ratios greater than 1.04. Peak h/l ratios correlated positively with amount of corticosterone in the feed.
In one experiment, chickens were inoculated iv with sheep erythrocytes at various times after consumption of feed containing corticosterone. Suppression of antibody responsiveness was most pronounced 4 hours later. Antibody responsiveness correlated positively with lymphocyte numbers.
Histologic examination of air sacs was made following euthanasia at various times after E coli exposure. Lesions observed in control chickens included: edema at 0.5 hour, beginning of heterophil infiltration at 1 hour, increased edema and heterophil infiltration at 2 hours, and severe edema and heterophil infiltration at 4 hours. Lesions were not observed in chickens that had been given feed containing 40 mg of corticosterone/kg of feed.
