Investigation of iodine transfer to milk in cows fed with corn silages with different nitrate and iodine contents

In this thesis study, the accumulation of iodine and nitrate in plants was investigated by applying low and high doses of iodine and nitrate under field conditions. Four experimental fields, covering a total of 160 decares, were established with varying levels of nitrate and iodine applications, and corn was cultivated for silage production. In the silage experiment, the effects of fermentation on nitrate and iodine concentrations in corn silages containing low and high levels of nitrate and iodine were examined. In the animal experiment, nitrate and iodine transfer levels into milk were investigated in Holstein dairy cattle fed with corn silages containing high and low levels of nitrate and iodine. The highest nitrate concentration in the corn plant was measured in the stalk (7487 ppm), while the lowest level was found in the young leaves (1044 ppm) (p<0,0001). The highest iodine concentration was detected in the old leaves (2084 ppb), whereas the lowest was found in the grain (2,9 ppb) (p<0,0001). Nitrate application to the soil increased plant nitrate levels, while iodine application increased plant iodine levels (p<0,0001). However, when nitrate was applied in addition to iodine, a significant decrease in plant iodine concentration was observed (p<0,0001). These decreases were more pronounced in the absence of iodine supplementation. After 60 days of fermentation, nitrate levels in corn silage decreased by 68,60% (p<0,001), and iodine levels decreased by 22,30% (p<0,0015). During fermentation, a high iodine concentration in the silage did not affect nitrate levels, nor did a high nitrate concentration affect iodine levels (p>0,05). In the animal feeding trials, high nitrate levels in the diet had no effect on nitrate transfer into milk (p>0,05). Similarly, feeding with high-iodine corn silage did not affect milk iodine concentration (p>0,05). Moreover, high nitrate levels did not influence iodine transfer into milk, and high iodine levels did not affect nitrate transfer into milk (p>0,05). At the end of the feeding experiment, no change was observed in milk nitrate concentration (p>0,05), whereas milk iodine concentration decreased by 50,90% (p<0,001). The lack of a clear effect in the feeding experiments was likely due to the presence of other forages in the ration containing relatively high levels of nitrate and iodine, which masked the potential effects of the experimental silages. In conclusion, nitrate and iodine accumulate in different amounts in different parts of the corn plant. As the levels of nitrate and iodine applied to the soil increase, their accumulation in the plant also increases. Nitrate inhibited the transfer of iodine from soil to plant, whereas iodine did not inhibit nitrate uptake. The fermentation process in corn silage reduced nitrate and iodine levels. In dairy cows fed diets containing nitrate and iodine, milk nitrate and iodine concentrations remained unchanged. Key Words: Corn silage; Fermentation; Iodine; Milk; Nitrate