Abstract: Abstract: Heat stress can increase the body temperature of a lactating dairy cow, thus impairing milk production and pregnancy. Severe cases of heat stress can even kill the animal, leading to serious economic loss. Effective heat-stress abatement has been one of the major goals in the dairy farm at present. Fortunately, the perforated air ducting (PAD) ventilation system can be expected to mitigate the heat stress in dairy cows. The targeted airflow can also be delivered to realize efficient cooling, due to its affordability and ease of installation. Previous studies have been designed to determine the effectiveness of the PAD systems. Particularly, the mathematical and numerical simulations have also been applied to assess the cooling performance of the system’s air jets. However, they cannot fully evaluate the performance of the system, particularly the desired microenvironment for every cow in every stall. It is often required to determine the heat-dissipation rates under ideal conditions. The cow’s physiological response to the PAD system can also be evaluated under real-world production. Therefore, this study aimed to compare the cooling performance of the PAD with the conventionally-ventilated (CV) system. A field experiment was also carried out to evaluate the local thermal environment, the stall occupancy rate, the ratio of time spent reclining and standing, as well as the skin-surface temperatures of a group of cows. The PAD and CV systems were also subjected to the same parameters. Results revealed that all jet velocities at the orifice centers exceeded 14.0 m/s and then remained relatively stable. The PAD system significantly improved the thermal environment by reducing the temperature (2.93 oC lower), increasing the relative humidity (15.43 percentage points RH higher) and air velocity (18.65 percentage points), compared with the CV system. Furthermore, the PAD system more efficiently mitigated the heat stress. The thermal indices (i.e., THI and ETIC) also decreased by 2.27 and 2.16 ℃, respectively. The PAD system achieved a higher average stall-occupancy rate in the ten days, compared with the CV system. Furthermore, the ratio of the reclining to standing cows was lower at the outset of the experiment in the PAD system, compared with the CV1. As the cows familiarized themselves with the PAD system, the ratio gradually increased and then equalled that of the CV1. The 0.49 ℃ lower temperatures of the forehead were registered by the standing cows that were subjected to the PAD system. Neither system achieved effective cooling when a cow was standing. Once a cow was reclining, the average shoulder-blade temperatures were 0.72 ℃ lower in the PAD system. While similar temperatures of the skin were recorded on the foreheads. Also, the PAD system provided a more uniform airflow to the cows when they were reclining. Overall, the PAD system significantly improved the local thermal environment to mitigate the heat stress among cows in the stall areas.