Comparing hair cortisol concentrations from various body sites and serum cortisol in Holstein lactating cows and heifers during thermal comfort zone

Measuring cortisol in hair has recently been established as a reliable physiological index to evaluate chronic stress conditions in humans and many animal species. The aim of this study was to determine serum cortisol and the concentrations of hair cortisol from various body sites of lactating Holstein cows and heifers during thermal comfort zone. Forty-seven multiparous lactating Holstein cows (average milk yield 37.5 ± 2.3 kgd−1, days in milk = 110 ± 47 days, body weight = 623 ± 75 kg) and 23 Holstein heifers (10-12 months of age, body weight = 258 ± 20 kg) were used in this study. Blood samples were collected on days (d) 0, 30, and 60 of the study. Hair samples were harvested from the forehead, withers, and rump sites of the animals. Data for temperature-humidity index (average THI = 69.3 ± 1.2) represented the threshold environmental conditions during the experiment. Serum cortisol concentration was higher on day 0 of the study and lower on day 30 and day 60 of sampling in lactating Holstein cows and heifers (P < 0.05). However, no differences in serum cortisol concentrations were observed in the second (day 30) and the third (day 60) samples in heifers and lactating cows (P < 0.05). No differences were found in hair cortisol concentrations among various sampling sites in lactating cows and heifers (P > 0.05). Conclusions drawn indicate that the distribution of cortisol into the hair shaft does not depend on hair sampling sites, and so that of the hair cut for cortisol analysis can be collected from any of the three body sites.