The content of heavy metals in the secretions of the mare's mammary gland should be tested not only because of the possibility of human consumption of mare's milk but also because of the influence of these elements on the development of suckling in the neonatal period and later in adolescence. The aim of the research was to assess the dependence of heavy metals concentration in the secretions of the mammary gland on the mare. Studies were carried out on 16 English Thoroughbred mares. Mares aged 4 to 19 years were divided into 2 research groups: Group Y - young mares 10 years of age (n = 8) Group O - mares older then10 years of age (n = 8) The experimental material, colostrum were collected before 12 hours after delivery and milk were collected on the 3rd day after foaling. The concentration of metals (Zn, Cu, Ni, Mn, Fe, Pb, Cd) was determined by the atomic absorption spectrometry (AAS apparatus Unicam 929 spectrometer). All elements (Ni, Zn, Cu, Mn, Fe, Cd) analysed in colostrum showed higher concentration in young mares. For Ni and Zn differences were significantly higher in young mares while for Mn and Cd those differences were highly significant. In analysed samples of milk Ni, Zn, Mn, Fe and Cd content were higher in young mares, while Cu content were higher in older mares. We reported highly statistical differences for Ni, Mn, and Fe.