The effects of improving barn cooling on the behaviour, physiological responses, gene expression, and milk yield of dairy cows.

Heat stress poses a significant challenge for dairy cows, particularly in warm climates, as it hampers their physiology, behaviour, and milk production. This study evaluated the effectiveness of a modern barn cooling system equipped with temperature-dependent fans in alleviating heat stress and enhancing cow welfare and productivity. The research was conducted on a large-scale Holstein Friesian dairy farm, comparing two high-yielding groups of around 100 cows each. The experimental group was housed in a barn with newly installed louvered, temperature-dependent circulation fans (providing high airspeed), while the control group remained in a barn with box ventilators (low airspeed). Data were collected over four three-day sampling periods during the summer. Environmental conditions were monitored using data loggers that recorded temperature and humidity, enabling calculation of the temperature-humidity index (THI). Cow body temperature was measured intravaginally. Additionally, time spent lying, eating, and ruminating was also tracked. Daily milk yields were obtained from the farm's database. Blood samples were also taken for gene expression measurements. Results indicated that THI values in both barns frequently surpassed the heat stress threshold (THI >68), yet air velocity in the experimental barn was notably higher (1.5-2.5 m/s) than in the control barn (0.2-0.5 m/s). Cows in the cooled barn showed significantly lower body temperatures in three of four periods. While lying time did not vary significantly, eating time increased in the experimental group later in the study. Moreover, milk yield was approximately 3 L/day higher (p < 0.05) in the experimental group. Enhanced ventilation led to complex changes in gene expression patterns, suggesting dynamic cellular responses to improved environmental conditions. These outcomes indicate that improved ventilation effectively reduces heat stress and supports better health, feeding behaviour, and milk production in dairy cows.