EN
Trace elements fulfil important functions in metabolism as constituents or effectors of enzymes, significance of the main trace elements - Fe, Mn, Zn, Cu, J, Co, Se in feeding animals was proved in years 1928 to 1957. In the next years there was found essentiality of the other elements (according to the time of discovering: Mo, Cr, Sn, V, F, Si, Pb and As). Some of them have been called ultra trace elements. Only seven of the above mentioned trace elements are officially ratified by the European Community to be used in feeding animals. Also the other elements, called elements accompanying as their physiological function is not known yet, are present in animal organisms. The optimal supply animals with trace elements could be determined by takink into account their content in feed and utilization in an animal - i.e. so - called bioavailability [3], Bioavailability is dependent on the absorbtion from the digestive tract and the utilization in metabolism processes.