Second Heat Wave Poses Greater Risk to Missouri Cattle

By Blake Jackson

While Missouri cattle may endure the first major heat wave of summer, the second often causes greater harm, according to University of Missouri Extension specialists.

Animals still recovering from earlier heat stress may struggle to handle another extreme weather event.

Tim Evans, MU Extension state specialist in veterinary toxicology and animal health, explains that cattle are especially vulnerable after the first bout of high temperatures. “Cattle may still be recovering from the first major heat event and be less resilient to future stresses,” he says.

It’s not just the heat alone that creates concern, adds MU Extension climatologist Zach Leasor. “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,” he says. High dew points also contribute, as increased atmospheric moisture reduces the animals' ability to cool down.

Experts point to four main reasons why a second heat wave can be more damaging:

• Cumulative heat load - Cattle need cooler nights to release built-up body heat. If nighttime temperatures stay high, heat continues to accumulate.
• Reduced resilience - Prolonged exposure weakens the animal's stress response.
• Lingering effects - Mortality risks remain high for up to three days after extreme heat ends.
• Lowered THI threshold - Extended heat reduces cattle’s ability to tolerate heat-humidity conditions, raising the risk of death.

Older or less healthy animals, those with low body condition scores, or certain breeds are more susceptible, says MU Extension beef nutritionist Eric Bailey. Cattle don’t sweat like many animals, relying instead on panting, drooling, open-mouth breathing, and restlessness to manage heat.

Bailey and Evans also warn of added danger for cattle grazing on tall fescue infected with toxic endophyte, which hinders heat dissipation.

MU Extension engineer Joe Zulovich emphasizes the importance of water and ventilation. “An ample water supply is the best heat abatement there is,” he says.

Other recommendations include offering shade, avoiding crowding, practicing fly control, working cattle in cooler times, and consulting with veterinarians before altering feed or management practices.

Photo Credit: gettyimages-jacqueline-nix