Traditionally, dairy cows in northern and central Europe were kept in tie-stalls and in closed stables. Nowadays, however, loose housing systems are preferred to reduce labour input with increasing herd sizes as well as to meet animal welfare requirements. This study aimed to assess whether cows are able to cope with the range of climatic conditions they are exposed to in open stables on commercial farms in central Europe. On each of four farms, ten lactating cows were observed over a total of five weeks in winter, spring and summer. Based on continuous measurements of air temperature and relative air humidity a mean value of a temperature humidity index (THI) was calculated for each farm and each observation day for night and day. THI had significant effects on skin temperature and body surface temperature both during night and day. Rectal temperature, duration of lying and cortisol concentration in the milk was significantly affected by THI during the day but not during the night. Heart rate and frequency of lying did not significantly covary with THI. The results of this suggest that climatic conditions prevalent on the farms during the day induce stronger thermoregulatory responses than the conditions during the night, but did not overtax the animal’s capacity to adapt. Consequently, the housing of dairy cows in open farm buildings should not result in animal welfare problems under the climatic conditions measured on the study farms.