The studies were conducted on a group of 20 mares of the Hucul breed kept in free range system. The horses made use of pastures in summer periods while being fed with hay or silage during the winter. Mares that bore offspring regularly, in good conditions and healthy were involved in the analysis. Hair samples of about 500 mg were taken from areas around the neck under the mane of each horse four times a year. The concentration of 6 elements, i.e., B, Ni, Si, Mo, I and Cr were measured in each sample. Much higher concentrations of molybdenum and nickel were found in hair samples collected in spring, but more of boron in autumn while those from winter contained more of chromium, silicon and iodine. The concentration of all the analyzed minerals differed significantly in relation to the season. A significant positive relationship between levels of nickel and molybdenum on the one hand as well as between silicon and chromium on the other was demonstrated. A negative correlation was, however, observed between the levels of iodine and molybdenum as well as between iodine and nickel.
