About Temperature and Humidity Index (THI)... As we feel humid and hot, milk cow is not only affected by temperature but humidity.
The Temperature and Humidity Index (THI) is calculated from the combination of temperature and humidity, so it is suitable for evaluating the heat stress on the milk cow rather than using each one alone.
About the relationship between THI and body temperature and fertility: When THI rises, the thermoregulating function decreases and the body temperature increases. The increase in THI and body temperature also have negative effect on the fertility.