Livestock Production Science 77 (2002) 349--353

The goal was to assess the impact that human interventions in natural ventilation may have on microclimatic factors in a barn and on thermal comfort of dairy cows housed there. Thermal comfort of the cows in the barn was assessed from the changes in their body surface temperature. Microclimatic factors in the barn were modified by opening and closing sidewall plastic curtains in the barn and doors in alleys. While no changes in the body surface temperature were recorded when the air temperature dropped by 3.1 8C, a significant response (P , 0.01) was recorded when the air temperature dropped by 6.5 8C. Significant changes in the air velocity at temperatures within the thermoneutral range influenced thermal conditions in the barn, and significant changes in body surface temperatures caused by vascular responses (P , 0.01, P , 0.05) were recorded. It is impossible to assess thermal comfort of dairy cattle housed in barns objectively only on the basis of visually detectable thermoregulatory behaviour of the cows or of microclimatic parameters measured in barns, because different combinations of air temperatures and air velocities will result different intensity of body surface cooling. This is reflected in the variations of the body surface temperatures, which can be reliably monitored by thermography