Variação estacional dos hormônios tireoideanos e do cortisol em ovinos em ambiente tropical

The variation of cortisol and thyroid hormones in Corriedale sheep bred in a tropical environment was evaluated. Fourteen males and seven females were observed in a climatic chamber at 45oC for nine days, eight hours per day. Rectal temperature (TR), respiratory rate (FR), air temperature (TA) and air humidity (PV) were recorded. The animals were ranked according to their responses for TR and FR and then the five highest (A group) and five lowest (NA group) ranked animals were selected. These ten animals were moved to a pen where they were observed along one year for TR and FR two times a day, and blood-sampled once a week. The results showed differences for T3, T4, and cortisol concentrations, which were attributed to variations in TA and PV. Cortisol concentrations were higher and T3 and T4 ones were lower under increased TA and PV. Correlations of TA and PV with cortisol values were r = .224 and r = .395 respectively. The negative correlations of TA with T3 (r = -.151) and T4 (r = -.156) showed that increase in TA may be followed by decrease in the metabolic rate. No significant difference for all variables investigated was found between the two groups, thus it is not recommended the use of TR and FR as the only criteria to evaluate sheep performance in tropical environments.