Effects of adrenocorticotropic hormone challenge and age on hair cortisol concentrations in dairy cattle

Abstract

Dairy cattle suffer stress from management and production; contemporary farming tries to improve animal welfare and reduce stress. Therefore, the assessment of long-term hypothalamic-pituitary-adrenal function using non-invasive techniques is useful. The aims in this study were: to measure cortisol concentration in cow and calves hair by radioimmunoassay (RIA), to test cortisol accumulation in bovine hair after adrenocorticotropic hormone (ACTH) challenges, and determine the influence of hair color on cortisol concentrations. Fifteen Holstein heifers were allotted to 3 groups (n = 5 each): in control group (C), just the hair was sampled; in the saline solution group (SS), IV saline solution was administered on days 0, 7, and 14; and the ACTH group was challenged 3 times with ACTH (0.15 UI per kg of body weight) on days 0, 7, and 14. Serum samples from the SS and ACTH groups were obtained 0, 60 and 90 min post-injection. Serum cortisol concentration was greater 60 and 90 min after injection with ACTH. Hair was clipped on days 0, 14, 28, and 44. Hair cortisol was methanol extracted and measured by RIA. Hair cortisol was preserved for 11 mo. Hair cortisol concentrations in the ACTH group were greater than in the saline and control groups on days 14 and 28, but not on day 44. Concentrations were greater in calves than in cows and greater in white hair than in black hair. Cortisol accumulated in bovine hair after ACTH challenges, but the concentration was affected by both age and hair color. If hair color effects are taken into account, assessing cortisol concentration in hair is a potentially useful non-invasive method for assessing stress in cattle.

Figure 1

Serum cortisol concentration in response to adrenocorticotropic hormone (ACTH) challenges. Three different ACTH challenges were performed on days 0, 7, and 14. Serum cortisol concentration (ng/mL mean ± standard error) was measured at time 0, 60, and 90 min after ACTH injection. The saline solution (SS) group of heifers received IV saline solution (n = 5); ACTH group was challenged with 0.15 UI/kg BW, IV, ACTH (n = 5). ^ab Differences between letters show statistical differences (P < 0.05).

Figure 2

Adrenocorticotropic hormone (ACTH) challenge induced response in hair cortisol concentration (pg/mg, mean ± S_x̄). Hair was collected on days 0, 14, 28, and 42 of the experiment. The ACTH challenge was done on days 0, 7, and 14. The control group (n = 5) received no injections. The saline solution (SS) group of heifers received saline solution (n = 5). The ACTH group (n = 5), challenged 3 times (1 wk apart) with ACTH. ^ab Differences between letters show statistical differences (P < 0.05).