<p><strong>Abstract.</strong> The objective of this study was to compare microclimatic conditions in three different housing systems designed for calf rearing – individual wooden hutches, individual tarpaulin hutches and individual pens under shelter – and to evaluate the thermal comfort of calves reared in these systems. Air temperature, relative air humidity and the rectal temperature of calves (n=324) were measured in the hutches and pens during three consecutive years. The hypothesis that

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... e climatic conditions of different housing system designs used in calf rearing affect the thermal comfort of calves was confirmed, as the design of the individual housing systems affected microclimatic conditions and subsequently the rectal temperature of the housed calves as well. Statistically significant differences (<i>P</i>&amp;lt;0.05) were found between the shelter and individual outdoor calf hutches in relation to the measured parameters. In the summer, the shelter showed a significantly (<i>P</i>&amp;lt;0.05) lower air temperature and significantly higher level of both relative air humidity and calf rectal temperature. These significantly higher rectal temperatures in both summer and in transitional periods (from March to June and from September to December) can be explained by microclimatic conditions and specifically by the combination of air temperature and the highest relative humidity that caused less comfortable microclimatic conditions for calves. The high relative humidity is probably caused by inadequate ventilation under the shelter. Therefore, new technology of calf housing under shelter could be recommended as suitable housing only if adequate ventilation is provided.</p>