DAFS-25k impact on cattle’s thyroid hormonal status

The paper studies the impact of selenium organic preparation DAFS-25k on thyroid capacity in pregnant cows. A stud farm which the work is done in is a biogeochemical province distinguished by a sharp deficit of selenium and iodine in the diet. DAFS-25k had been implanted into the animals subcutaneously during 1 month 30 days before the predicted calving. A sterile 0.6 % DAFS-25k oil solution was used in doses containing 2 mg/cow/day, 6 mg/cow/day and 12 mg/cow/day. It was found that the cows’ diet is deficient in iodine and selenium by 63 and 82 % respectively. Daily use of selenium in DAFS-25k in the dose range causes a decrease in the concentration of free thyroxine due to deiodination activating by selenium dependent deiodinases of the first and second types. Consequently, there is a progressive increase in the blood content of total triiodothyronine in all experimental animals as relating to the background values. In this case, the concentration of thyroid-stimulating hormone decreases in blood serum by the 30th day according to the principle of negative feedback. In control animals, an increase in the serum concentration of thyroid-stimulating hormone reached the point 1.8 by the 30th day, total triiodothyronine increased by 14 and 19 % by the 21st day and the 30th day respectively, while the concentration of free thyroxine was reduced by 19 % by the 30th day. The use of selenium in the setting of iodine deficiency leads to aggravation of iodine deficiency.