Protective Action Needed
Less than 130
Heat stress is not an issue.
130 to 150
Horses will sweat but can stay safe if water intake is adequate.
None, as long as water intake is adequate.
More than 150 (and relative humidity above 75%)
Heat dissipation through sweating may be a problem.
Limit exercise and check horses frequently for signs of stress.
More than 180
Heat dissipation through sweating fails.
Stop all workouts.