Behavioural effects of embryonic exposure to corticosterone in chickens

We tested the hypothesis that exposure of chick embryos to corticosterone leads to increased fear, reduced competitive ability, reduced ability to cross a barrier and reduced growth in juvenile chicks. Behaviour was studied in birds subjected to three different egg injection treatments: a negative control (no treatment of eggs), a positive control (100 μl sesame oil vehicle) and a corticosterone treatment (0.6 μg corticosterone in 100 μl sesame oil). Eggs were injected prior to incubation and the behaviour of chicks was studied during the first 4 weeks of life. Corticosterone treatment increased fear in chicks, as indicated by greater avoidance of an observer in the home pen at 2 weeks of age (P < 0.0001), reduced ability to cross a wall to access feed at 2 weeks of age (P < 0.05) and reduced ability to compete for a wormlike object at 4 weeks of age (P < 0.01). Treatment with corticosterone also reduced body weight at 1 week of age (P < 0.003) and 4 weeks of age (P < 0.04), but not at hatch (P < 0.28). The sesame oil vehicle reduced fear (P < 0.0001), but had no other significant effects. These results indicate that embryonic exposure to corticosterone leads to behavioural and growth deficits in chicks.