“If air temperature does not drop at night, you’ve got a huge problem, especially if this continues for a period of days. If ambient air temperature drops below 70ºF, the animals have a window for heat loss and can often recover.
If it stays in the upper 70s or higher, they accumulate heat,” explains Spiers.
“The rough formula we use: If a heat wave lasts for longer than three days, you will start to see animals dying. If cattle don’t have the opportunity to cool off at night, to get rid of the body heat, each day their temperature creeps higher. It can have a major adverse effect on them after three days,” he says.
“If you can create a break in the heat before you get to that point, you may prevent losses. You need to find ways to break that cycle (with sprinklers, shade, fans, etc.) if it doesn’t break naturally,” says Spiers.
“If cattle are outdoors, you can hope for clear nights with no clouds, to get some radiant heat loss. The sky is a heat sink, if you have clear nights. But if it’s cloudy, the heat sink is blocked and the cattle can’t get rid of the heat,” he says.
Spiers teaches a course at the university on environmental and stress physiology that deals with heat and other environmental stressors. It will be an online course next year.
One version may be tailored to students and another version for producers. He hopes to help educate producers about the effects of heat stress. 
This article originally appeared in print with "Heat stress impacts cattle health."
