Factors other than air temperature and relative humidity can also impact heat stress. The
presence of sunshine can add several degrees to the THI, whereas wind can lower it by a
few points because it brings cooler air to the animal and carries away excess heat.
In dairy cattle, milk production is seriously affected once the THI rises above 78. As can be
seen in this chart, a THI of 78 occurs at 31'C and 40% relative humidity, or 27'C and 80%
relative humidity. Conception rates fall once THI is above 72, which is equivalent to 2S'C at
SO% relative humidity