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The effects of environmental changes during different seasons on hair cortisol concentration were evaluated as a stress biomarker in Hanwoo cattle. Nine cattle, including dams, heifers and calves (body weight (kg) = 545 +/- 93.9, 380.7 +/- 68.5 and 53.7 +/- 1.4 and ave. age (months) = 55.9 +/- 13.6, 17.2 +/- 0.3 and 1.8 +/- 0.6, respectively), were examined in this experiment. Hair samples were harvested on Aug 25, Oct11, Nov11 and Dec 23 of 2017 and on Feb 12 of 2018. Repeated-measures analyses were performed using the mixed procedure of SAS software. Lower hair cortisol concentration was observed in Oct compared with Feb and in Nov compared with Feb (P < 0.05). The hair cortisol concentration in Aug did not differ from those for the other dates. No differences were observed in the hair cortisol concentration of dams or heifers at different dates. In calves, higher hair cortisol concentration was observed in Aug vs. Oct and in Aug vs. Nov and lower hair cortisol concentration was observed in Oct vs. Feb and in Nov vs. Feb (P < 0.05). Relatively higher hair cortisol concentration was found in calves than dams in Aug and Feb and then heifers in Aug (P < 0.05). The effect of time (sampling date) and cattle type and the interactions between dam and calf, heifer and calf, and cattle and time were highly significant (P < 0.01). In conclusion, Hanwoo calves were relatively more susceptible to intense environmental conditions than were heifers and their dams. (C) 2019 Friends Science Publishers