Egg Corticosterone Concentrations After Acute Stress Exposure in Free Range Hens with Different Range Usage

Free range hens are exposed to various potential stressors including weather conditions and risk of predation (Gilani et al., 2014). Distress can result in impaired biological functions including reduced reproduction, immunity and growth (Palme, 2012). In order to investigate the impact of early range usage, corticosterone concentrations in egg albumen were measured in response to a stressor (manual handling and relocation) in free range hens.

Two groups (n = 625) of commercial free range hens were selected based on their individual range usage between 18 and 22 weeks of age: “Stayers (S)” accessed the range for 3.51±0.3 days while “rangers (R)” accessed the range for 14.9±0.2 days on an average. At 22 weeks of age, these hens were exposed to “stressors” (being caught, confined for ~10 h, weighed, and rehomed into a new partition within the same area and the same bird numbers). Ninety eggs of each group were randomly collected immediately after the release (baseline– representing pre-stress corticosterone concentrations), 7 days, and 20 weeks later. Ninety eggs were also randomly collected from the other 36,875 hens located in the same shed (negative control group, NC, no experimental stressors, calculated avg. range use 10.73±0.12). Corticosterone concentrations of the albumen were analysed using a Radio Immune Assay (Downing and Bryden, 2008). Data analysis was performed using a one way ANOVA (SPSS v.24, IBM Corp., Armonk, NY, USA).

Initially, egg corticosterone concentrations of S were lower compared to both R and the NC group (4.32±0.1, 5.12±0.2, and 4.90±0.2ng/g respectively; P=0.03; figure 1). While corticosterone concentrations of R and NC hens decreased within the first 7 days to 4.67±0.2ng/g; P=0.04 and 4.22±0.2; P=0.01, the values of S increased (4.60±0.1; P=0.06). In all groups, corticosterone concentrations decreased over time and reached their lowest point at week 20 (S: 3.35±0.1, R: 3.3±0.1, NC: 3.4±0.1ng/g; P=0.627). The reasons for the low initial corticosterone concentrations in S require further investigation.