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The objectives of this study were to examine heat stress conditions dynamically at cow level, to investigate the relationship to the climate conditions at stationary locations inside a dairy barn and to compared the climate conditions at cow level between primiparous and multiparous cows. The study was conducted on a commercial dairy farm in Sachsen-Anhalt, Germany from May 2014 to July 2014. The herd consisted of 1,200 Holstein dairy cows with an average milk production of 10,147 kg. The barn was positioned in a NE-SW orientation with open ventilation and a mechanical fan-system. Ambient temperature and relative humidity were recorded in 2 minute intervals using EL-USB-2+ data loggers (Lascar electronics, Salisbury, UK) and used to calculate the THI according to the equation reported by the NRC (1971): THI = (1.8 × AT + 32) – ((0.55 – 0.0055 × RH) × (1.8 × AT – 26)). Stationary climate conditions within the barn were recorded on 2 locations within the milking parlor (holding area and rotary parlor) and on 3 locations within the experimental pen (alley, cetral, and window position). Climate conditions at cow level were recorded with climate loggers attached to the collar of the cows within an isolated rubber tube. Sixtyone primiparous and 62 multiparous cows were enrolled in the study. The AT and THI differed significantly between all stationary loggers. The lowest AT, RH and THI was measured at the window logger in the experimental pen and the highest AT and THI was measured at the central logger in the experimental pen. The highest RH was measured at the holding area logger. The AT and THI measured at the mobile cow loggers were 1.56 °C an 2.33 THI points (P<0.05) higher than measured at the stationary loggers, respecively. The mean daily THI was higher at the mobile cow loggers than at the stationary loggers on all experimental days. There was no significant difference for the AT, RH, and THI between primiparous and multiparous cows. The THI at the pen loggers was 0.44 THI points (P<0.05) lower when the experimental cow group was located inside the milking parlor. The THI measured at the mobile cow loggers was 1.63 THI points (P<0.05) higher when the experimental cow group was located inside the milking parlor. Our results indicate, that the actual heat stress experienced of dairy cows differs significantly from the heat stress conditions measured at stationary locations inside the barn. Thus, a wide range of microclimates exists between different locations as well as between individual cows exists inside a dairy barn. Heat stress is underestimated when climate conditions are obtained from one stationary location inside the barn.