Cortisol and DHEA concentrations in the hair of dairy cows managed indoor or on pasture

This study was conducted in order to assess the changes of cortisol and dehydroepiandrosterone (DHEA) concentrations in hair of Italian Simmental dairy cows managed indoor in tie-stall barns or grazing on high mountain pasture. In experiment I, animals were kept in tie-stalls throughout the year (n = 27). In experiment II, animals remained on mountain pastures during summer (from 20th June to 20th September) and then kept indoors in tie-stalls for the rest of the year (n = 18). At the end of July, following vertical transhumance, dairy cows were moved to a pasture located at a higher altitude. In the two studies, hair samples, obtained using clippers from the animal's forehead, were collected on the 20th June (P1), 20th July (P2), 20th August (P3), 20th September (P4) and 20th October (P5) and analysed for cortisol and DHEA. In experiment I, DHEA concentration was unaffected by sampling time (P > 0.05), whereas, cortisol/DHEA ratio was similar between P1 and P2 (P > 0.05) and then increased during the experimental period reaching the highest value at P5 (P < 0.05). In experiment II, dairy cows had higher concentration of DHEA during grazing compared to cows kept indoors (P < 0.05), conversely cortisol/DHEA ratio decreased from P1 to P2 (P < 0.05), remained constant from P2 to P3 (P > 0.05) and then increased from P3 to P4 (P < 0.05), the highest value was recorded at P5. In conclusion, cortisol and DHEA concentrations and their ratio measured in the hair of dairy cows can be useful to evaluate the allostatic load in animals managed indoor in tie-stall barn or grazing on mountain pasture.