Selenium (Se) is an essential element significantly influencing health status of animals and humans. The insufficient supply of organism with this element leads to many disorders. Conversely, higher intake can be toxic. As a part of selenoproteins, it regulates the antioxidant system and thus prevents the oxidative destruction of biological membranes and prevents the damage of the body by heavy metals. Consequently, its deficiency disrupts the overall health of animals and humans because of involvement of selenium compounds in many biological functions. Selenium concentration of plant biomass is derived from its content in the soil and may considerably vary depending on the region. One of the defense mechanisms how plants respond to the occurrence of heavy metals is the synthesis of phytochelatins. Phytochelatins (PCs) are polypeptides capable of binding the risk elements in chelate complexes. Their synthesis does not take place in ribosomes but using the phytochelatinsynthetasy enzyme. After binding of the heavy metals in chelate complexes, they are transported to the vacuoles, thereby preventing the toxic effect of metals in the cytosol. According to some authors, the synthesis of phytochelatines initiates not only the presence of heavy metals (most often cadmium) but also selenium. Red clover (Trifolium pratense L.) is considered as one of the most important crops. It is a perennial herb (2-4 years). As the fodder is usually grown in a pure culture or in the combination with grass or in a mixture. Forage contains a high proportion of protein and vitamins. It is fed on pasture or used to produce hay or silage
