Peat contains a large number of water-soluble components. The risk of feeding animals with peat as a supplement has only been thoroughly studied from the aspect of the effect of humic substances. Humic substances are natural constituents of the food chain, present in all plant and animal organisms. Humic acids do not induce goitre, but may enhance the goitrogenic effect of low iodine (Huang et al., 1994). HAs are the most widespread natural polymers derived from biological, chemical and microbial decomposition of organic matter. According to the summary by Yang et al. (2004), Ha’s represent a group of natural high molecular weight macro- molecules composed of aromatic rings forming a very complex structure in the presence of phenolic, hydroxyl, phenolic hydroxyl, ketonyl, quinone, semiquinone, carboxyl, carbonyl and alkoxyl groups. The HAs often form complexes with a mixture of metallic elements. Because of the above-mentioned data, one cannot expect that two separate natural sources of HAs can contain identical molecules. Humic substances of medicinal importance are found abundantly in peat, sapropel, and other humified sources Ref: Laub, R. J. Process for preparing synthetic soil-extract materials and medicaments based thereon. U.S. Patent 5,945,446, 999. The biological effects of humic substances can be different, depending on their chemical structure and physicochemical properties and the quinone functional group of Fulvic acid. Chemical composition, structure, and functional groups can vary greatly, depending on the origin and age of the humic substance and the conditions of the humification process (humidity, aeration, temperature, mineral microenvironment, etc. Ref: Chen, J.; Gu, B.; LeBoeuf, E. J.; Pan, H.; Dai, S. Spectroscopic characterization of the structural and functional properties of natural organic matter fractions. Chemosphere 2002, 48, 59-68.