Measurement of corticosterone in the plasma, eggs and faeces of laying hens

Abstract

Context Stress responses in chickens are commonly assessed from measurements of corticosterone in blood, but there is an increasing research effort to develop non-blood means of assessing the activity of the hypothalamo–pituitary (HPA) axis. It is common to measure corticosterone in the eggs and faeces. Aims We extended previous work by undertaking a study of caged laying hens comparing basal concentrations of corticosterone in plasma, faeces, egg albumen and egg yolk on a between-cage basis. We tested the hypothesis that there are positive relationships between corticosterone in plasma and corticosterone in each of the other matrices. Methods Blood samples were collected from each bird at a single point in time. In Experiment 1, these comparisons (between plasma concentrations of corticosterone on Day 1 and egg albumen, egg yolk and faecal concentrations of corticosterone on Days 1, 3 and 4 of the study) were made for hens of two ages under basal conditions, whereas, in Experiment 2, the comparisons (between plasma concentrations of corticosterone on Day 3 and egg albumen, egg yolk and faecal concentrations of corticosterone on Days 1 and 2 of the study) were made for hens housed at different space allowances with and without access to a nest box. The birds without a nest box had not had experience with a nest box prior to sampling. Key results There was a statistically significant (P = 0.012), but limited, positive relationship between plasma and egg albumen concentrations of corticosterone under basal conditions in Experiment 2. There were no other statistically significant (P > 0.05) relationships in either experiment. These results suggest that measures of corticosterone in the albumen, yolk and faeces of laying hens are unlikely to be robust predictors of basal concentrations of corticosterone in the blood. Conclusions Although there was some indication that concentrations of corticosterone in albumen may be related to concentrations in blood under basal conditions, based on all the results, this suggestion is made cautiously. Implications More comprehensive research is required to establish if measures of corticosterone in egg components and faeces are related to chronic basal activity of the hypothalamo–pituitary axis in laying hens. There is also a need to understand the impact of corticosterone on production, reproduction and welfare in hens from measures in both blood and non-blood matrices.