April/May 2024 NEBRASKA CATTLEMAN 15 with extreme heat following precipitation, adding additional moisture and humidity to the environment can actually exacerbate the situation, Woiwode explains. Nevertheless, sprinkling can be a strategy to use, particularly if airflow is present. Getting cattle wet can increase evaporative cooling and reduce the ground temperature. This is most beneficial when there has not been a significant amount of precipitation recently and humidity is low. Before a heat event occurs, Woiwode suggests planning to have cattle in pens that naturally have more airflow and strategizing ways to improve airflow. • CLUE #1: Predicted hot weather following precipitation. It is the combined temperature and humidity that determines the severity of heat stress. • CLUE #2: Monitor the upper critical temperaturehumidity limits of cattle. Consider this limit has been reached when the Temperature-Humidity Index reaches 80 (e.g., 86° F at 60 percent relative humidity; see Table 1). • CLUE #3: Evening weather forecast for overnight temperatures to remain above 70° F. A potential heat stress crisis situation exists for cattle when there is little or no night cooling. • CLUE #4: Observing cattle will tell you when they are becoming uncomfortable from heat. Cattle will start to walk around looking for an area that is more comfortable, where there is more air movement. They will start to slobber, and their respiratory rate may reach 75 breaths per minute. They will extend their head to make it easier to breathe. They will position their body to minimize their exposure to the sun; generally, this is facing the sun. Clues to an Impending Heat Stress Crisis CONTINUED ON PAGE 16 Table 1: Temperature-Humidity Index (THI) Source: “Managing Feedlot Heat Stress” UNL NebGuide, Sept. 2007
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