Prepare Cattle for Second Heat Wave

By Julie Harker and Linda Geist

The first heat wave of summer can have negative effects on Missouri cattle, but it’s the second heat wave causes the most damage, say University of Missouri Extension specialists.

MU Extension state specialist in veterinary toxicology and animal health Tim Evans says cattle may still be recovering from the first major heat event and be less resilient to future stresses.

MU Extension climatologist Zach Leasor says it is not just high temperatures that are concerning. “Environmental factors such as high overnight lows (over 70 degrees), minimal cloud cover, little air movement and high relative humidity compound heat stress in cattle and other animals,” Leasor says.

Also concerning are high dew points, he says. Dew point marks the temperature at which water turns into liquid droplets. The higher the dew point, the more moisture in the air and the more uncomfortable it becomes.

Animal scientists attribute potential damage from a second heat wave to four major causes:

• Cumulative heat load. Cattle rely on lower temperatures at night to rid themselves of accumulated heat. When nighttime temperatures remain high, cattle have a hard time recovering, and body heat continues to build.

• Reduced resilience. Long periods of heat weaken the animal’s ability to cope.

• Prolonged effects. Even after a heat wave ends, risk of cow mortality remains high for three days, according to research.

• Lowered THI (temperature-humidity index) threshold. Prolonged heat stress lowers cattle’s THI threshold, which increases risk of death. High humidity makes it hard for cattle to regulate their body temperatures.