Hair cortisol and DHEA levels in dairy cows reared on summer pastures.

Cortisol and DHEA are involved in adaptive and constructive coping strategies response to environmental changes. The aim of this study was to examine changes in hair cortisol and DHEA concentrations (and consequently their ratio) produced in response to a change from indoor winter to summer grazing conditions in dairy cows. The study population comprised 15 dairy cows from one single herd. Hair samples were obtained using electric razor from the animal's forehead at the time points: 0 (ST1), 30 (ST2) and 60 days (ST3) after the start of summer grazing. Hair cortisol concentrations increase during the first month of grazing from ST1 to ST2 (1.29 ± 0.083 pg/mg vs. 1.64 ± 0.120 pg/mg; P 0.05). The hair DHEA concentrations were higher during grazing, ST2, than in stall, ST1 (342.06 ± 17.594 pg/mg vs. 200.40 ± 9.989 pg/mg; P 0.05). The cortisol to DHEA ratio decreased during the first month of grazing (6.58 ± 0.480 pg/mg vs. 5.04 ± 0.578 pg/mg; P 0.05). During transition from winter housing to high mountain conditions variations in hair cortisol and DHEA levels are produced that suggest that the HPA axis reacts to environmental changes such as changes in social groups, diet, housing, and transport. Data suggest that even if animals undergo important environmental change moving from winter housing to summer highland grazing maintain the resilience. A beneficial impact of summer grazing on the health of dairy cows may be evaluated using hair matrix