“Cows are much more cold tolerant than we are and much less heat tolerant than we are,” says Jeffrey Bewley, University of Kentucky College of Agriculture assistant extension professor in the Department of Animal and Food Sciences. “Of course, even in the Southeast, we experience winter days where cold stress is a concern. But, interestingly in Kentucky, the number of days cows experience heat stress is much higher than the number of days cows experience cold stress.”

Bewley said cows begin to experience heat stress when the temperature humidity index exceeds 72 degrees F. Bewley and University of Kentucky undergraduate student Curtis Coombs, looked at historical temperature data from nine different weather stations in Kentucky. While the average number of days where the temperature humidity index exceeds 72 degrees F. varies within the state, the average across Kentucky is 125 days.

“Perhaps more surprisingly, these locations averaged at least one day with heat stress conditions in every month of the year except December and January,” Bewley says. “Yes, that means heat stress can be an issue even in February, March, October and November. The take-home message from this information is that dairy barns in Kentucky should be built or renovated to help cows deal with heat stress first with consideration of cold stress second.”

During warmer temperatures, poor ventilation may result in cows expressing obvious signs of heat stress, such as breathing heavily or panting. Research has illustrated that average lying-down time decreased from 10.9 to 7.9 hours per day as temperature increased. Thus, cows may alter stall usage if barns are not adequately ventilated.

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Source: University of Kentucky