CYCLIC VARIATIONS OF CORTISOL, TRIIODOTYRONINE (T3) AND TYROXINE (T4) ON BEFORE AND AFTER PARTURITION OF QUARTER HORSE MARES VARIAÇÕES CÍCLICAS DO CORTISOL, TRIIODOTIRONINA (T3) E TIROXINA (T4) NO PERIPARTO DE ÉGUAS DA RAÇA QUARTO DE MILHA

This study was designed to evaluate changes in plasma concentrations of cortisol (Cs), triiodothyronine (T3) and thyroxine (T4), as well as their circadian rhythm during peripartal period of Quarter Horse mares. Eighteen clinically healthy mares, with age between 60 and 96 months and alive weight (AW) between 350 and 420 Kg were divided in three groups (n=6) according the reproductive status, that means: no pregnant (TE), Pregnant (GE) and after parturition (PA).The blood samples were taken during 24 hours in intervals of two hours.There was no differences between cortisol levels regarding the reproductive status and periods of blood samples collections. This hormone showed a circadian rhythm, with accentuated oscillation in TE, but small for GE and PA. For T3 and T4 there was difference between reproductive status (P