ACTH and Control Injection Data (WBC differential count, serum corticosterone and cortisol concentrations) for 6, 17, and 26 WOA Pullets

<p>The avian stress pathway is poorly understood but activation of the hypothalamic-pituitary-adrenal (<strong>HPA</strong>) axis through an internal stressor like adrenocorticotropic hormone (<strong>ACTH</strong>) administration generally results in elevations of glucocorticoids like corticosterone and cortisol in the blood. Additionally, white blood cell populations can be altered. Specifically, the heterophil:lymphocyte (H:L) ratio is often elevated during periods of stress. However, in wild birds the stress pathway is often down-regulated early in life. A few chicken studies found the opposite result where the stress pathway was up-regulated in early development.</p>

<p>In order to evaluate age effects of stress pathway activation in laying hens, ten each of Lohmann LSL-Lite hens received either a saline-mannitol or synthetic human ACTH injection at 6, 17, and 26 weeks of age. Prior to injections as well as one and two hours post-injection, blood was collected and WBC differential counts and H:L ratios were determined by a boarded clinical pathologist (N=10/treatment). Serum corticosterone and cortisol levels were measured using a liquid chromatography (<strong>LC</strong>) system coupled to a mass spectrometer (MS/MS) (N=5/treatment). At 26 weeks of age, egg albumen samples were collected and corticosterone and cortisol were measured using a liquid chromatography (<strong>LC</strong>) system coupled to a mass spectrometer (MS/MS) (N=5/treatment).</p>

<p>Plasma corticosterone was unaffected by treatment and egg albumen corticosterone and cortisol were below detectable limits at all time points for both treatments. Serum cortisol increased 1 hour after injection in the ACTH group at all ages, this was significant at 17 WOA (P<0.0001). The H:L ratio was not affected by treatment but heterophils increased and lymphocytes decreased in the ACTH group compared to the control group, this difference was only significant at 26 WOA (P<0.0004).</p>

<p>The results of this study suggest that the H:L ratio is not an accurate measure of acute HPA axis activation during the pullet phase and that plasma corticosterone and albumen corticosterone and cortisol are not accurate measures of acute HPA axis activation during the pullet or adult phases. Cortisol may have some utility in capturing a physiological stress response in pullets and adult hens.</p>