Concentrações plasmáticas de testosterona, triiodotironina (T 3) e tiroxina (T 4) em bodes submetidos ao estresse calórico

Abstract

To verify the effect of heat stress (HS) on plasma testosterone, triiodothyronine (T 3), and thyroxine (T 4) concentrations, eight Saanen (n=4) and Alpine Brown (n=4) bucks were kept in climate chamber under thermal neutral conditions (13.0°C to 26.7°C) for 30 days. After a resting period (60 days), the same bucks were submitted to heat stress (23.7°C to 34.0°C) for another 30 days. To neutralize the seasonal variations of hormonal profiles throughout the period, the photoperiod was controlled every 30 days altering long (16 hours of light and 8 hours of darkness) and short days (8 hours of light and 16 hours of darkness). The blood samples were collected twice a week during five weeks. In both breeds, there was no effect of HS (P>0.05) on plasma concentrations of testosterone (1.8±0.2 vs 1.3±0.2ng/ml) and T 4 (52.7±2.8 vs 50.0±2.8ng/ml). There was a decline (P<0.01) of plasma T 3 concentrations (1.3±0.1 vs 1.0±0.1ng/ml) after HS treatment, but this reduction was only evident in Saanen bucks. In both breeds, the plasma concentrations of T 3 and T 4 varied (P<0.01) according to the day of blood sample collection. The HS was sufficient to provoke a physiological response with reduction of plasma concentrations of thyroid hormones mainly of T 3 in Saanen bucks, but not in Alpine ones. The HS did not affect the plasma testosterone and T 4 levels. © 2009 Escola de Veterinária UFMG.