This research evaluated the thermal efficiency of two evaporative cooling systems, sprinkler and misting, associated with forced ventilation, on the dairy cows thermal stress relief. The study was carried out in a commercial dairy cattle farm located in São Pedro city, state of Sao Paulo, Brazil. The duration of the experiment was twenty-eight consecutive days of November 2003, and 10 Holstein cows lodged in a freestall barn were studied. The relative humidity, the dry bulb temperature and black globe temperature were registered every 15 minutes, during all experimental period. Among these cows, five were selected for collecting physiological data (respiratory frequency, rectal temperature and temperature in white and black surfaces) at 9:00 a.m., 11:00 a.m., 1:00 p.m., 3:00 p.m. and 5:00 p.m., during nine non-consecutive days. According to the results, it was concluded that both of the cooling systems studied did not cause any significant differences on the rectal temperature, respiratory frequency and temperature in black surface. However, the temperature in white surface was significantly lower in the sprinkling system, at the time of 11 a.m. and 1 p.m. The misting system reduced significantly the wet bulb temperature, black globe temperature and humidity index, when compared to the sprinkling system. Both cooling systems reduced the maximum wet bulb temperature of the barn compared to the external environment.
heat stress; sprinkler; thermal comfort
