Comparison of hair cortisol levels and body temperature response prior to and post heat stress and water deprivation in Holstein dairy cows

This study carried out in Holstein dairy cows between July and September 2013 for 74 days, when the temperature-humidity (THE) index indicates heat stress conditions. To investigate the effects of water deprivation and THE on prolonged stress indicator (hair cortisol) and body temperature responses in dairy cows hair cortisol (HC) levels and body temperature at different body sites were evaluated. Thirty dairy cows (53.5 ± 30.4 days in milk; DIM; 650 ± 53 kg BW) were allotted into two groups of free access to water (FAW; 15 cows) and 2 hours water deprivation (2hWD; 15 cows) following feeding. The animals were subjected to having the hair cut (1 to 2 gram) from their foreheads at the same time (12:00 h) twice at the beginning (prior to the beginning of heat stress) and the end of the experiment when the cows were under THE (Highest temperature and humidity of 38 ?C and 91%, and lowest ones of 22 ?C and 65%). Hair cortisol levels (initial hair cut as the baseline and re-grown hair) were measured using ELISA method. Body temperature (BT) was measured twice daily at 7 body points of cows including rectum, vagina, hip, udder, rumen-side (flank), ear, and forehead using non-contact forehead infrared thermometer (infrared gun having two modes; inner and skin; CEM, Rev. 090709, Shenzhen Everest Machinery Industry co.Ltd., China, the sensitivity of 0.01) on the 7 d of the beginning and the last 7 d of the experiment at 10:00 and 14:00 h. Statistical analyses carried out using the MIXED model of SAS as a repeated measurements. The intra-assay and inter-assay coefficients of variations for hair cortisol measurements were 3.15 and 10.05, respectively. The HC levels were not different (p > 0.05) between the two groups; however, HC level was significantly higher (p < 0.0001) in post heat stress conditions than prior to. No temperature differences were observed in all of the body points, inner and skin, between the two groups (p > 0.05). However, there was a tendency of higher skin temperature in the 2hWD groups than in the FAW group (p = 0.093). Conclusions drawn indicate water deprivation following feeding for 2 hours is not influential enough to increase hair cortisol as the prolonged indicator of stress conditions in dairy cows; however, heat stress conditions act as a strong stressor by increasing hair cortisol levels in both groups compared with thermo-neutral zone conditions.