Forming of temperature-humidity index (THI) and milk production of cows in the free-stall barn during the period of summer heat*

Evaluated were changes of temperature and relative air humidity inside a free-stall barn affecting the welfare of cows of three technological groups during a hot summer. The effects of selected microclimate parameters of the barn have been assessed based on the THI (temperature-humidity index) in relation to milk production. The research revealed that the animals suffered from thermal stress which resulted in decreased milk production in particular groups. The paper presents information about percentage values of this decrease and time needed to regain the original state. It also points out the need to determine THI not only for the entire barn but also for its various zones occupied by particular technological groups of cows with different levels of milk production. The authors highlight that the THI index is quite a useful tool for predicting thermal stress in particular sections of the barn. Yet, it is necessary to improve the methodology of THI calculation in order to include more microclimate elements, mainly air movement.