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Body Temperature Responses and Hair Cortisol Levels in Dairy Holstein Cows Fed High- and Low-Forage Diet and Under Water Deprivation During Thermal-Humidity Exposure

Abstract Body temperature responses and hair cortisol levels in dairy Holstein cows fed high- and low-forage diet and under water deprivation during thermal-humidity exposure (THE) were evaluated. Two experiments (Exps.) were conducted between July and September 2012 and 2013 for 64 d and 74 d, respectively. First, twenty dairy Holstein cows (90±30 DIM; 37.2±1.7 l milk/d, 620±75 kg BW) were used. The practical forage:concentrate (F:C) ratios in the low forage (LF) and high forage (HF) group were 44:56 and 56:44, respectively, while they were designed to be 40:60 and 60:40. Second, thirty dairy cows (53.5±30.4 DIM; 41.7±1.5 l milk/d,650±53 kg BW) were allotted into two groups of free access to water (FAW) and 2 h water deprivation (2hWD) following feeding. The animals were subjected to having the hair cut (1 to 2 g) 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. 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) on the 7 d of the beginning and the last 7 d of the experiment at 1000 and 1400 h. Statistical analyses were carried out using the MIXED model of SAS as repeated measurements. The intra-assay and inter-assay coefficients of variations for hair cortisol measurements were 3.15 and 10.05, respectively. Hair cortisol (HC) levels were not different within the two groups in both Exps. (P>0.05); however, HC level was lower (P<0.0001) prior to temperature-humidity exposure (THE). Results of Exp. 1 showed that vagina inner temperature was higher (P=0.041) and rectal temperature tended to be higher (P=0.083) in the HF compared to the LF group. The inner ear temperature was lower and ear skin temperature was higher (P=0.032) in the HF compared to the LF group. Forehead inner temperature was higher (P=0.048) in the LF group than in the HF group while forehead skin temperature was lower in the HF group (P=0.041). No differences were observed in the hip, udder and rumen-side (flank) temperature (both in body and skin) between the HF and LF group (P=0.012). In Exp. 2, no temperature differences were observed at all of the body points, inner and skin, between the two groups (P>0.05). However, the skin temperature in the 2hWD groups tended to be higher than in the FAW group (P=0.093). Conclusions drawn indicate the beneficial use of measuring BT at different body points of the cow in addition to RT under THE.