Analysis of the possible influence of Solar activity on the number of days with a high temperature-humidity index

At elevated temperatures and humidity, cattle experience heat stress which, depending on its intensity, can lead to reduced productivity, health problems and even mortality. At the same time, some animals are currently kept in free-range conditions and this practice is increasing as it is believed to be more beneficial for the socialisation of the animals. It is therefore essential to monitor the health of animals during periods of high temperatures and to take appropriate measures to ensure their well-being. The temperature-humidity index (THI) is a threshold heat index suitable for the physiology of dairy cattle. In Russia, it is generally accepted that the threshold for stress begins at a THI of 75 or higher. Accordingly, this level was used as the boundary at which moderate heat stress develops. Analysing the number of days on which the THI reaches stress levels over time is important in determining the extent of the impact of climate change on cow health. This can help to identify factors that contribute to an increase or decrease in these days and to develop strategies to adapt to changing climate conditions. Therefore, the aim of this study was to determine the number of stressful days over a relatively long period of time in the Central Region of Russia and to attempt to establish a correlation with external factors influencing the climate, such as solar activity. This study shows that the number of days with temperature indices (THI) greater than or equal to 75 is likely to be related to solar activity, albeit with a one-year lag, which most likely indicates an indirect mechanism of this influence. At the same time, another factor has been identified, occurring on average every five years, which significantly influences the number of THI≥75 days, but does not seem to be related to solar activity.