This work was carried out with the objective to study the annual behavior of thermo regulators traits in dairy cows. Two hundred cows were used during two consecutive years and the respiratory rate (RR), rectal temperature (RT), as well as a blood sample was collected for triiodothyronin (T3) and thyroxin (T4) dosages, were recorded. Air temperature and humidity were also recorded and the black globe humidity index (BGHI) and radiant heat load (RHL) were calculated in the same days of data collection. There was no significative effect of the year for the majority of studied variables, however, the effects of month of collection and herd were significative for all variables. All values of RT were inside of the amplitude of normality, indicating homoeothermic condition. The RR was altered in every seasons of the year and herds, showing a constant necessity of thermolisys. In herds with higher RT and RR, there was a reduction T3 and T4 liberation. In seasons of higher BGHI and RHL, there was increase in the RT, followed for higher RR and lower T3 and T4 plasmatic concentrations.
dairy cattle; thermal stress; thermoregulation
