Effects of organic and inorganic selenium supplements on serumic levels of thyroid hormones in mixed breed horses

Selenium has an important role in the metabolism of thyroid hormones because it is necessary in the conversion ofthyroxine (T4) to its active form triiodothyronine (T3). For this conversion, selenoenzymes which are mainly located in the liver and kidneys are necessary. This study was conducted to determine the effects of organic and inorganic selenium (Se) supplementation on serumic levels of thyroid hormones in mixed breed horses. For this purpose, 10 healthy mixed breed horses 4-5 years of age were randomly divided into two equal groups. The first treatment group received routine diet plus premix (1 mg sodium selenite/day) for 12 days and the second group was supplemented similarly with 1 mg commercially available yeast enriched organic selenium (O-Sel). Blood samples were taken by venoject tubes from the jugular vein on days 0, 3, 6 and 12. Serumic selenium concentrations were measured using atomic absorption and serum thyroid hormones were measured by spectrophotometer. After selenium supplementation, mean serum T3 levels increased significantly in both treatment groups (p<0.05) while T4 concentrations decreased. According to the results, administration of limited amounts of selenium can increase the active form of thyroid hormones with a positive impact on the performance of the horse.