Q. Why is this a top resource article? "Research continues to focus on ways to alleviate heat stress through genetic advancement and knowledge around genes that are important in alleviating heat load, hormonal manipulation such as the use of human chorionic gonadotropin to improve pregnancy retention, feed additives that potentially reduce core body temperature and, lastly, advancements in cooling systems and areas of opportunities with cooling such as dry cows." —Todd Bilby, Merck Animal Health The Temperature-Humidity Index (THI) is a valuable measure that you know when cows are becoming heat-stressed and to what degree so you can use cooling methods appropriately. Heat stress is caused by a combination of temperature, relative humidity, solar radiation, air movement and precipitation. The majority of studies on heat stress in livestock focus on the two main environmental stressors: temperature and relative humidity (RH).