One of the negative factors of ionizing radiation on the body is the formation of active oxidants, which are protected by the antioxidant system. The effect of high doses of radiation on the antioxidant system of animals has been studied well, but there is not enough information about the long‐term effects of low doses. The study of the effect of pre‐threshold radiation doses on the main indicators of antioxidant protection of cattle was the purpose of our research. The research was carried out in JSC "Osminskoye" of Slantsevsky district and JSC "Plemzavod " RAPTI" of Luga district of Leningrad region on healthy lactating cows aged 3–4 years in the amount of 8 heads from each farm. Radio ecological characteristics of agricultural land JSC "Osminskoe" was as follows‐the density of radioactive contamination of the soil on 137Cs more than 1 Ci/km2, the power of the exposure dose on the ground 35–48 μr/h. Similar indicators of land in JSC "Plemzavod" RAPTI " were less than 0.5 Ci/km2 and 6–19 μr / h. Both farms use their own fodder base (hay, silage, root crops), concentrated feed produced by JSC "LKKZ", the animals are kept in summer walking, which allows us to talk about a similar dose load due to external and internal irradiation. In cows, catalase activity was determined in serum, and malone dialdehyde concentration and superoxide dismutase activity were determined in plasma. The results of the study showed that the activity of superoxide dismutase in cows from JSC "Osminskoye" was 4.15±0.46 U/mg Hb, catalase ‐ 14.54±1.03 mkat/l, and the level of Malon aldehyde ‐ 3.71±0.68 μmol/l. Similar indicators in animals from JSC "Plemzavod "RAPTI" were as follows ‐ 6.3±0.75 U/mg Hb, 9.77±0.62 mkat/l and 2.23±0.12 μmol/l. Intergroup differences of the studied indicators were statistically significant. Analyzing the results of the study, we can say that chronic stimulation of the antioxidant system by active oxidants leads to a decrease in the level of superoxide dismutase in cows by 34.1%. Probably, as compensation, there is an activation of other enzymes, in particular, an increase in catalase activity by 1.5 times. However, the compensatory capabilities of other elements of the antioxidant system are not able to fully neutralize free radicals, as evidenced by an increase in the concentration of malon dialdehyde by 66.4%.The study shows that cows long‐term in conditions of higher pre‐threshold doses of external and internal radiation occurs chronic oxidative stress, manifested by an imbalance of individual links of the antioxidant system.
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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