Egg corticosterone: a noninvasive measure of stress in egg-laying birds

Quantitative measures of corticosteroids in biological samples that can be obtained noninvasively, such as saliva, feces, and body hair, have important potential as contributing elements in assessing the quality of captive environments and the severity of experimental procedures. Egg-laying chickens may be of particular interest because the corticosterone contents of the egg may have potential as a convenient measure of preceding adrenocortical activity. To develop methods to reliably quantify corticosterone content in the egg white and yolk, corticosterone content in eggs from 15 egg-laying chickens housed in single production cages were compared with that of eggs from 15 sister chickens, group housed in 1450 cm2 cages equipped with bedding, straw nests, sand baths, and perches. Approximately 80% of the total amount of corticosterone in the eggs was found in the yolk, and there was a positive correlation between yolk corticosterone concentration and total egg corticosterone (r = 0.90, n = 30, P < .001). The egg white contained approximately 20% of the total amount of corticosterone, but there was no correlation between concentrations in the white and the total corticosterone content of the eggs (r = 0.003). There was no difference in the white and yolk corticosterone concentrations or total egg corticosterone between singly housed and group-housed egg-laying hens. Quantitative analyses of corticosterone concentration in eggs may assist when analyzing the stressfulness of experimental procedures and major changes to the birds' environment that affect the activity of the hypothalamus-pituitary-adrenal axis.