Mitigating heat stress of dairy cows bred in a free-stall barn by sprinkler systems coupled with forced ventilation

This paper presents the results of a research study which had the objective of investigating the effect of a sprinkler system coupled with forced ventilation on the heat stress of dairy cows bred in a free stall barn without paddock. To this aim, an experiment was carried out inside a free-stall dairy house equipped with two different cooling systems: a fogging system associated with forced ventilation in the resting area and a sprinkler system associated with forced ventilation in the feeding alley. The experiment regarded two adjacent pens of the barn and was constituted by three different trials carried out in the following periods: 27^th June - 7^th July (P1), 25^th July - 4^th August (P2), 24^th August - 3^rd September (P3). The experimental protocol of each trial required that the treatment group was housed in one pen where the two cooling systems were always activated following an established timetable, whereas the control group was housed in the other pen, where the sprinkler system associated with forced ventilation was always deactivated. Climatic parameters were measured inside each pen of the barn and outside. Then, thermal humidity index (THI) was calculated. Rectal temperature and respiration rate of a sample of dairy cows were monitored each day during the three periods considered (P1, P2 and P3). During the three trials the cows of both groups were subjected to climatic conditions that resulted in average daily THI values between 72.8 and 74.7, corresponding to mild or moderate heat stress. However, during daytime, air temperature and relative humidity reached values corresponding to a severe heat stress, as attested by the maximum THI values that were higher than or very close to 80. Furthermore, it was observed that the sprinklers do not influence the microclimatic conditions. However, the physiological parameters values of the treatment group were always significantly lower than the corresponding ones of the control group. Specifically, the system especially influenced the respiration rate that, in the treatment group, was close to 50 breath/min, while in the control group it reached 70 breath/min. The sprinkler system had more limited effects on rectal temperature that, however, in the treatment group was significantly lower than in the control group (38.7°C to 38.8°C vs 39.1°C to 39.4°C) in all the three periods of the experiment. These results show that the sprinkler system could be useful to mitigate heat stress in dairy cows.