The pilot researches were conducted in Wielkopolska. They aimed initial identifi cation of cows reaction on changing of THI, which are likened to temperature and humidity conditions of air. The subjected cows characterize with high productivity, exceeding 40kg of milk per day, independently from lactation stages. The results display that the day s production of raw milk, as well as fat and protein content, do not only depend on lactation stage but also on the value of THI factors. Higher THI is accompanied by loss in the weight of milk and drop in its technological utility. The climate warming may escalate the risk of production loss during the heats.