Understanding and avoiding heat stress in cattle can be a valuable management tool in Oklahoma, where most areas of the state experience 70 or more days each year with temperatures that exceed 90 degrees Fahrenheit.

“Cattle have an upper critical temperature that is approximately 20 degrees Fahrenheit cooler than humans,” said Greg Highfill, Oklahoma State University Cooperative Extension area livestock specialist. “When we’re uncomfortable at 80 degrees and feel hot at 90 degrees, cattle may well be in the danger zone for extreme heat stress.”

The potentially bad news does not end there. Humidity is an additional stress that intensifies ambient temperature problems by making body heat dissipation more difficult. In other words, it can be tough to cool off in Oklahoma during the summer, for people and cattle.

High humidity contributes to the likelihood of heat stroke or prostration because water evaporation from the oral and nasal cavities is decreased, in spite of rapid panting, a heat regulatory device in cattle.

“Since cattle sweat very little, the primary mechanism they have to remove internal heat is by breathing the warm air out of their body, which is accomplished much more efficiently in low humidity environments,” Highfill said.

Signs of heat stress include slobbering, heavy panting, open mouth breathing and lack of coordination. Severe cases may include depression and trembling that require some type of low stress intervention.

“If water is applied to cattle for cooling, it is important that a large droplet size be applied,” Highfill said. “Misting water does not reach the hide and only adds humidity to the breathing environment.”