The values of the temperature-humidity index and its influence on the performance parameters of dairy cows were monitored on four farms located in the southern part of the central Slovakia during a period of three years. The observed parameters included: the milk yield per cow per day, average milk speed and maximum milk speed. The thermal-humidity index was calculated based on a formula. The individual periods were divided according to the achieved THI. The results of dairy cows with a milk yield of 29 kg to 31 kg show that there is not a decrease in the milk yield per milking if the THI value is lower than 68. It was also found that there was a decrease in the milk yield per dairy cow in the robotic milking parlor for a THI value greater than 72. The influence of a THI value higher than 68 in these dairy cows results in a higher average milk speed, as well as a higher maximum milk speed. These two parameters are not yet in the main area of research interest. This study enriches the area with new knowledge, according to which dairy cows can show thermal stress by increasing the milk speed as well as the maximum milk speed.

The paper presented is dedicated to investigation of the temperature-humidity index (THI) and its impacts on the performance parameters of dairy cattle. These parameters were recorded at four farms in the central Slovakia; the experiments took place three years. These parameters comprised milking time, time spent in the milking box, and connection time. The THI was calculated according to the standard formula and individual periods were established on the basis of achieved THI values. The results showed that the milking time and the time spent in the milking box were not reduced when the THI ranged from 68 to 71, with a daily milk yield of 28.96 kg. If the THI exceeded 72, the milking time and the time spent in the milking box were shortened, which was statistically confirmed. However, even with a daily milk yield of 31.27 kg, a reduction in the milking time and time spent in the milking box was reduced. This was caused by the THI higher than 68, which was also statistically confirmed. Based on the results obtained, the dairy cows respond to heat stress by reducing the milking time and reducing time spent in the milking box.