Serum thyroxin (T4) and cortisol concentrations in Bosnian and Herzegovinian mountain horses

The serum concentrations of hormones are widely used to diagnose thyroid and adrenocortical diseases in animals. The objectives of the present study were, for the first time, to determine serum thyroxine (T4) and cortisol values in Bosnian and Herzegovinian mountain horses, and to investigate the influences of age and gender on T4 and cortisol levels. Blood samples were collected on the stud farm Borike from 23 apparently healthy horses of both sexes aged between two and twenty-three years. Horses were grouped in three age classes: young mature horses, middle-aged horses and old horses. Serum samples were analyzed for T4 and cortisol concentrations. The T4 values ranged from 6 to 45 nmol/L with a mean ±SD of 22.83±8.32 nmol/L. The cortisol values ranged from 149 to 190 nmol/L with a mean ±SD of 171.57±11.46 nmol/L. Values of T4 decreased with increasing age (p=0.021). Mean value of T4 in young mature horses was 27.60 nm/L, in middle-aged horses was 19.40 nm/L and in old horses was 18.33 nm/L. Values of T4 were significantly higher (p=0.031) in females (24.88 nm/L) than in males (18.14 nm/L). Negative significant correlation between age and hormone concentration was observed for T4 (r = -0.431; p = 0.040). Differences between gender or age classes for cortisol values were not significant. The mean total serum T4 and cortisol values in Bosnian and Herzegovinian mountain horses were in the normal reference ranges for horses, and both age and gender significantly affected T4 levels