It does not have to be 110 F degrees for heat stress to occur in dairy cows. Studies have found that at temperatures as low as 78 F, dairy cows will begin to cut feed intake and lose body weight.
Milk production falls.
Reproductive performance, health, and lactational performance are affected. Heat stress will continue to affect performance even in the cooler months ahead. High yielding cows are most susceptible to heat stress. The degree of heat stress suffered by the cow will depend on the combination of environmental conditions - air temperature, relative humidity, air movement, and radiation from the sun. In southern states where the heat and humidity is more severe dairymen have also used sprinklers to provide added cooling effects.