Abstract
Heat stress in dairy cows is one of the leading causes of decreased production and fertility. Increasing air velocity, using ceiling fans, to enhance convective heat transfer and accordingly body heat dissipation is highly required. However, this might have negative effects such as increasing emission mass flux of the harmful gases. Therefore, this study aims at investigating the effect of ceiling fans on the dairy cows, air velocity profiles, and the distribution of gaseous concentrations throughout a naturally ventilated dairy barn. Three air velocity measurements campaigns, with two repetitions each, were carried out during summer season 2010. The air velocity was measured inside the barn using ultrasonic anemometers. The air temperature and humidity were measured using temperature-humidity sensors. The climatic data were recorded by weather station. The concentrations of CO2, NH3, CH4, and N2O were measured using a multi-gas monitor. The heat stress was estimated by determining the Temperature-Humidity Index (THI). A thermal infrared imaging camera was used to investigate the heat relief from the cows and freestalls under 2 conditions, which were: ceiling fans on and ceiling fans off. The results showed that the implementation of ceiling fans reduced the THI from 79 (significant stress) to 68 (no stress). The average air velocities were 0.98 and 0.59 m s-1 as the ceiling fans were “on” and “off”, respectively. It was concluded that the ceiling fans have cooling effect, alleviate the heat stress, and enhance the air movement and distribution throughout the barn. However, the ceiling fans indirectly increase the ventilation rates in higher potential then the disguised decrease of the gaseous concentrations, which ultimately results in increasing the gaseous emissions. 1Assistant Professor, Depart. of Agric. Eng., Faculty of Agriculture, Cairo University, Egypt 2Research Scientist, Leibniz Institute for Agric. Eng. Potsdam-Bornim (ATB), Potsdam, Germany Therefore, a balance must be achieved among the different contradictions: air velocity optimization, heat stress alleviation, air distribution enhancement, and gaseous emissions reduction.
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