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 30 th 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 30 th day, total triiodothyronine increased by 14 and 19 % by the 21 st day and the 30 th day respectively, while the concentration of free thyroxine was reduced by 19 % by the 30 th day. The use of selenium in the setting of iodine deficiency leads to aggravation of iodine deficiency.
In experiments on mice the study of the radioprotective and radiotherapeutic efficacy of the combined use of the selenium-containing feed additive DAFS-25k and the iodine-containing preparation Monclavit-1 was carried out. It has been shown that intragastric administration of DAFS-25k oil solution 3 hours before the total, external, single exposure to γ-radiation, and the subsequent (in 12 hours) intragastric administration of an aqueous solution of Monclavit-1, increases the survival rate of irradiated animals to 67% versus 17% in the control animals. The mechanisms of radioprotective efficacy are assumed to be the antioxidant activity of selenium compounds in DAFS-25k, normalization of thyroid function and relief of gastrointestinal syndrome due to the pronounced antimicrobial activity of Monclavit-1.
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